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Collins + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Steam Turbines + A Book of Instruction for the Adjustment and Operation of + the Principal Types of this Class of Prime Movers + +Author: Hubert E. Collins + +Release Date: January 2, 2009 [EBook #27687] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK STEAM TURBINES *** + + + + +Produced by Chris Curnow, David Cortesi, Brett Fishburne, +Nikolay Fishburne and the Online Distributed Proofreading +Team at https://www.pgdp.net + + + + + + +</pre> + + +<p><span class='pagenum'><a name="Page_i" id="Page_i">[i]</a></span></p> +<div id="titlepage"> +<h3>THE POWER PLANT LIBRARY <br /> + +<img src="images/i000.png" alt="publisher ad" title="publisher ad" /> +</h3> + +<hr class="major" /> + +<h1> +STEAM TURBINES +</h1> + +<h2> +A BOOK OF INSTRUCTION<br /> +FOR THE ADJUSTMENT AND OPERATION OF<br /> +THE PRINCIPAL TYPES OF THIS<br /> +CLASS OF PRIME MOVERS +</h2> + +<h3> +compiled and written<br /> + +by<br /> + +HUBERT E. COLLINS +</h3> + +<h3> +<i>FIRST EDITION</i><br /> + +Second Impression +</h3> + +<p class="center" style="margin-top:4em;line-height:1.5em;"> +<span style="font-size:larger;">McGRAW-HILL BOOK COMPANY, <span class="smcap">Inc</span>.</span><br /> +239 WEST 39TH STREET, NEW YORK<br /> +<span style="font-size:smaller;">6 BOUVERIE STREET, LONDON, E. C.</span></p> + +<hr class="major" /> +<p class="center"> +<i>Copyright</i>, 1909, <span class="smcap">by the Hill Publishing Company</span></p> +<hr /> +<p class="center"> +<i>All rights reserved</i> +</p> +</div> + + + + +<hr class="major" /> +<h2><a name="TRANSCRIBERS_NOTES" id="TRANSCRIBERS_NOTES"></a>TRANSCRIBER'S NOTES</h2> + +<p>The author of this book used the spellings "aline," "gage," and "hight" +for the conventional spellings "align," "gauge," and "height." As they +are used consistently and do not affect the sense, they have been left +unchanged. Some obvious typos and misspellings that do not affect the sense +have been silently corrected. The following substantive typographical +errors have been corrected: +"being" to "bearing" (p. <a href="#Page_68">68</a>); +"FIG. 50" to "FIG. 56" (p. <a href="#Page_91">91</a>), +and "Fig. 2" to "Fig. 73" (p. <a href="#Page_159">159</a>). +Two other likely errors have been left as queries: +lead/load on p. <a href="#Page_142">142</a> +and beating/heating on p. <a href="#Page_177">177</a>. +These five changes are indentified by +dotted red underlining with pop-up titles.</p> + +<p> +The numerous figures from the original are reproduced here as 16-level +grayscale images in .PNG format, scaled to no more than 512 pixels +width to fit a small window. When an image is enclosed in a broad gray +border, it is linked to a higher-resolution version; click to open it. +</p> + + +<hr class="major" /><p><span class='pagenum'><a name="Page_vi" id="Page_vi">[vi]</a></span></p> +<h2><a name="INTRODUCTION" id="INTRODUCTION"></a>INTRODUCTION</h2> + + +<p><span class="smcap">This</span> issue of the Power Handbook attempts to +give a compact manual for the engineer who feels the +need of acquainting himself with steam turbines. To +accomplish this within the limits of space allowed, it +has been necessary to confine the work to the description +of a few standard types, prepared with the +assistance of the builders. Following this the practical +experience of successful engineers, gathered from +the columns of <i>Power</i>, is given. It is hoped that the +book will prove of value to all engineers handling +turbines, whether of the described types or not.</p> + +<div> +<span class="smcap" style="margin-left:10em;">Hubert E. Collins.</span><br /> +<span class="smcap">New York</span>, <i>April</i>, 1909. +</div> + + + +<hr class="major" /> +<p><span class='pagenum'><a name="Page_vii" id="Page_vii">[vii]</a></span></p> + +<h2><a name="CONTENTS" id="CONTENTS"></a>CONTENTS</h2> + +<ol class="TOC"> +<li><span class="smcap">The Curtis Steam Turbine in Practice</span> <span class="pgno"><a href="#Page_1">1</a></span></li> +<li><span class="smcap">Setting the Valves of the Curtis Turbine</span> <span class="pgno"><a href="#Page_31">31</a></span></li> +<li><span class="smcap">Allis-Chalmers Steam Turbine</span> <span class="pgno"><a href="#Page_41">41</a></span></li> +<li><span class="smcap">Westinghouse-Parsons Turbine</span> <span class="pgno"><a href="#Page_58">58</a></span></li> +<li><span class="smcap">Proper Method of Testing a Steam Turbine</span> <span class="pgno"><a href="#Page_112">112</a></span></li> +<li><span class="smcap">Testing a Steam Turbine</span> <span class="pgno"><a href="#Page_137">137</a></span></li> +<li><span class="smcap">Auxiliaries for Steam Turbines</span> <span class="pgno"><a href="#Page_154">154</a></span></li> +<li><span class="smcap">Trouble with Steam Turbine Auxiliaries</span> <span class="pgno"><a href="#Page_172">172</a></span></li> +</ol> + +<hr class="major" /> + +<p><span class='pagenum'><a name="Page_1" id="Page_1">[1]</a></span></p> + +<h2><a name="I_THE_CURTIS_STEAM_TURBINE_IN_PRACTICE1" id="I_THE_CURTIS_STEAM_TURBINE_IN_PRACTICE1"></a> +I. THE CURTIS STEAM TURBINE IN PRACTICE<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a></h2> + + +<div class="footnote"> +<p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"> +<span class="label">[1]</span></a> +Contributed to <i>Power</i> by Fred L. Johnson.</p> +</div> + +<p>"<span class="smcap">Of</span> the making of books there is no end." This +seems especially true of steam-turbine books, but the +book which really appeals to the operating engineer, +the man who may have a turbine unloaded, set up, +put in operation, and the builders' representative out +of reach before the man who is to operate it fully +realizes that he has a new type of prime mover on +his hands, with which he has little or no acquaintance, +has not been written. There has been much published, +both descriptive and theoretical, about the turbine, +but so far as the writer knows, there is nothing in +print that tells the man on the job about the details +of the turbine in plain language, and how to handle +these details when they need handling. The operating +engineer does not care why the moving buckets +are made of a certain curvature, but he does care +about the distance between the moving bucket and +the stationary one, and he wants to know how to +measure that distance, how to alter the clearance, +if necessary, to prevent rubbing. He doesn't care +anything about the area of the step-bearing, but he +does want to know the way to get at the bearing to +take it down and put it up again, etc.</p> + +<p><span class='pagenum'><a name="Page_2" id="Page_2">[2]</a></span>The lack of literature along this line is the writer's +apology for what follows. The Curtis 1500-kilowatt +steam turbine will be taken first and treated "from +the ground up."</p> + +<p>On entering a turbine plant on the ground floor, the +attention is at once attracted by a multiplicity of +pumps, accumulators and piping. These are called +"auxiliaries" and will be passed for the present to +be taken up later, for though of standard types their +use is comparatively new in power-plant practice, and +the engineer will find that more interruptions of service +will come from the auxiliaries than from the +turbine itself.</p> + + +<h3>Builders' Foundation Plans Incomplete</h3> + +<p>It is impractical for the manufacturers to make +complete foundation drawings, as they are not familiar +with the lay-out of pipes and the relative position of +other apparatus in the station. All that the manufacturers' +drawing is intended to do is to show the +customer where it will be necessary for him to locate +his foundation bolts and opening for access to the +step-bearing.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_1" name="FIG_1"></a> +<span class='pagenum'><a name="Page_3" id="Page_3">[3]</a></span> + <img src="images/i003.png" + alt="FIG. 1" + title="FIG. 1" + /><br /> +FIG. 1</p> +</div> + +<p>Fig. <a href="#FIG_1">1</a> shows the builders' foundation drawing, +with the addition of several horizontal and radial tubes +introduced to give passage for the various pipes which +must go to the middle of the foundation. Entering +through the sides of the masonry they do not block +the passage, which must be as free as possible when +any work is to be done on the step-bearing, or lower +guide-bearing. Entering the passage in the foundation, +<span class='pagenum'><a name="Page_4" id="Page_4">[4]</a></span> +a large screw is seen passing up through a circular +block of cast iron with a 3/4-inch pipe passing through +it. This is the step-supporting screw. It supports +the lower half of the step-bearing, which in turn supports +the entire revolving part of the machine. It is +used to hold the wheels at a proper hight in the +casing, and adjust the clearance between the moving +and stationary buckets. The large block which with +its threaded bronze bushing forms the nut for the +screw is called the cover-plate, and is held to the +base of the machine by eight 1-1/2-inch cap-screws. On +the upper side are two dowel-pins which enter the +lower step and keep it from turning. +(See Figs. <a href="#FIG_2">2</a> and <a href="#FIG_3">3</a>.)</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_2" name="FIG_2"></a> + <img src="images/i005.png" + alt="FIG. 2" + title="FIG. 2" + /><br /> +FIG. 2</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_3" name="FIG_3"></a> + <img src="images/i006.png" + alt="FIG. 3" + title="FIG. 3" + /><br /> +FIG. 3</p> +</div> + +<p>The step-blocks are very common-looking chunks +of cast iron, as will be seen by reference to Fig. <a href="#FIG_4">4</a>. +The block with straight sides (the lower one in the +illustration) has the two dowel holes to match the +pins spoken of, with a hole through the center threaded +for 3/4-inch pipe. The step-lubricant is forced up through +this hole and out between the raised edges in a film, +floating the rotating parts of the machine on a frictionless +disk of oil or water. The upper step-block has +two dowel-pins, also a key which fits into a slot across +the bottom end of the shaft.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_4" name="FIG_4"></a> + <img src="images/i007.png" + alt="FIG. 4" + title="FIG. 4" + /><br /> +FIG. 4</p> +</div> + +<p>The upper side of the top block is counterbored to +fit the end of the shaft. The counterbore centers the +block. The dowel-pins steer the key into the key-way +across the end of the shaft, and the key compels +the block to turn with the shaft. There is also a +threaded hole in the under side of the top block. This +<span class='pagenum'><a name="Page_7" id="Page_7">[7]</a></span> +is for the introduction of a screw which is used to pull +the top block off the end of the shaft. If taken off +at all it must be pulled, for the dowel-pins, key and +counterbore are close fits. Two long bolts with threads +the whole length are used if it becomes necessary to +take down the step or other parts of the bottom of +the machine. Two of the bolts holding the cover-plate +in place are removed, these long bolts put in +their places and the nuts screwed up against the plate +to hold it while the remaining bolts are removed.</p> +<p><span class='pagenum'><a name="Page_8" id="Page_8">[8]</a></span></p> + + +<h3>How to Lower Step-Bearings to Examine Them</h3> + +<p>Now, suppose it is intended to take down the step-bearings +for examination. The first thing to do is to +provide some way of holding the shaft up in its place +while we take its regular support from under it. In +some machines, inside the base, there is what is called +a "jacking ring." It is simply a loose collar on the +shaft, which covers the holes into which four plugs +are screwed. These are taken out and in their places +are put four hexagonal-headed screws provided for the +purpose, which are screwed up. This brings the ring +against a shoulder on the shaft and then the cover-plate +and step may be taken down.</p> + +<p>While all the machines have the same general appearance, +there are some differences in detail which may +be interesting. One difference is due to the sub-base +which is used with the oil-lubricated step-bearings. +This style of machine has the jacking ring spoken of, +while others have neither sub-base nor jacking ring, +and when necessary to take down the step a different +arrangement is used.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_5" name="FIG_5"></a> +<span class='pagenum'><a name="Page_5" id="Page_5">[5]</a></span> + <img src="images/i009.png" + alt="FIG. 5" + title="FIG. 5" + /><br /> +FIG. 5</p> +</div> + +<p>A piece of iron that looks like a big horseshoe (Fig. <a href="#FIG_5">5</a>) +is used to hold the shaft up. The flange that covers +the entrance to the exhaust base is taken off and a +man goes in with the horseshoe-shaped shim and an +electric light. Other men take a long-handled wrench +and turn up the step-screw until the man inside the +base can push the horseshoe shim between the shoulder +on the shaft and the guide-bearing casing. The men +on the wrench then back off and the horseshoe shim +<span class='pagenum'><a name="Page_9" id="Page_9">[9]</a></span>supports the weight of the machine. When the shim +is in place, or the jacking ring set up, whichever the +case may be, the cover-plate bolts may be taken out, +the nuts on the long screws holding the cover in place.</p> + +<p>The 3/4-inch pipe which passes up through the step-screw +is taken down and, by means of the nuts on the +long screws, the cover-plate is lowered about 2 inches. +Then through the hole in the step-screw a 3/4-inch rod +with threads on both ends is passed and screwed into +the top step; then the cover-plate is blocked so it +cannot rise and, with a nut on the lower end of the +3/4-inch rod, the top step is pulled down as far as it +will come. The cover-plate is let down by means of +the two nuts, and the top step-block follows. When +it is lowered to a convenient hight it can be examined, +and the lower end of the shaft and guide-bearing will +be exposed to view.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_6" name="FIG_6"></a> +<span class='pagenum'><a name="Page_6" id="Page_6">[6]</a></span> + <img src="images/i010.png" + alt="FIG. 6" + title="FIG. 6" + /><br /> +FIG. 6</p> +</div> + +<p>The lower guide-bearing (Fig. <a href="#FIG_6">6</a>) is simply a sleeve +flanged at one end, babbitted on the inside, and slightly +<span class='pagenum'><a name="Page_10" id="Page_10">[10]</a></span>tapered on the outside where it fits into the base. The +flange is held securely in the base by eight 3/4-inch cap-screws. +Between the cap-screw holes are eight holes +<span class='pagenum'><a name="Page_11" id="Page_11">[11]</a></span>tapped to 3/4-inch, and when it is desired to take the +bearing down the cap-screws are taken out of the base +and screwed into the threaded holes and used as jacks +to force the guide-bearing downward. Some provision +should be made to prevent the bearing from +coming down "on the run," for being a taper fit it +has only to be moved about one-half inch to be free. +Two bolts, about 8 inches long, screwed into the holes +that the cap-screws are taken from, answer nicely, as +a drop that distance will not do any harm, and the +bearing can be lowered by hand, although it weighs +about 200 pounds.</p> + +<p>The lower end of the shaft is covered by a removable +bushing which is easily inspected after the guide-bearing +has been taken down. If it is necessary to take +off this bushing it is easily done by screwing four 5/8-inch +bolts, each about 2 feet long, into the tapped +holes in the lower end of the bushing, and then pulling +it off with a jack. (See Fig. <a href="#FIG_7">7</a>.)</p> + +<p>Each pipe that enters the passage in the foundation +should be connected by two unions, one as close to +the machine as possible and the other close to the +foundation. This allows the taking down of all piping +in the passage completely and quickly without disturbing +either threads or lengths.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_7" name="FIG_7"></a> +<span class='pagenum'><a name="Page_12" id="Page_12">[12]</a></span> + <img src="images/i012.png" + alt="FIG. 7" + title="FIG. 7" + /><br /> +FIG. 7</p> +</div> + + +<h3>Studying the Blueprints</h3> + +<p>Fig. <a href="#FIG_8">8</a> shows an elevation and part-sectional view +of a 1500-kilowatt Curtis steam turbine. If one should +go into the exhaust base of one of these turbines, all +that could be seen would be the under side of the +<span class='pagenum'><a name="Page_14" id="Page_14">[14]</a></span> +lower or fourth-stage wheel, with a few threaded holes +for the balancing plugs which are sometimes used. +The internal arrangement is clearly indicated by the +illustration, Fig. <a href="#FIG_8">8</a>. It will be noticed that each of +the four wheels has an upper and a lower row of buckets +and that there is a set of stationary buckets for each +wheel between the two rows of moving buckets. These +stationary buckets are called intermediates, and are +counterparts of the moving buckets. Their sole office +is to redirect the steam which has passed through the +upper buckets into the lower ones at the proper angle.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_8" name="FIG_8"></a> +<span class='pagenum'><a name="Page_13" id="Page_13">[13]</a></span> + <a href="images/i013H.png"> + <img src="images/i013.png" + alt="FIG. 8. ELEVATION AND PART-SECTIONAL VIEW OF A 1500-KILOWATT CURTIS TURBINE" + title="FIG. 8. ELEVATION AND PART-SECTIONAL VIEW OF A 1500-KILOWATT CURTIS TURBINE" + /> + </a><br /> +FIG. 8. ELEVATION AND PART-SECTIONAL VIEW OF A 1500-KILOWATT CURTIS TURBINE</p> +</div> + +<p>The wheels are kept the proper distance apart by +the length of hub, and all are held together by the large +nut on the shaft above the upper wheel. Each wheel +is in a separate chamber formed by the diaphragms +which rest on ledges on the inside of the wheel-case, +their weight and steam pressure on the upper side +holding them firmly in place and making a steam-tight +joint where they rest. At the center, where the hubs +pass through them, there is provided a self-centering +packing ring (Fig. <a href="#FIG_9">9</a>), which is free to move sidewise, +but is prevented from turning, by suitable lugs. This +packing is a close running fit on the hubs of the wheel +and is provided with grooves (plainly shown in Fig. <a href="#FIG_9">9</a>) +which break up and diminish the leakage of steam +around each hub from one stage to the next lower. +Each diaphragm, with the exception of the top one, +carries the expanding nozzles for the wheel immediately below.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_9" name="FIG_9"></a> + <img src="images/i015.png" + alt="FIG. 9" + title="FIG. 9" + /><br /> +FIG. 9</p> +</div> + +<p>The expanding nozzles and moving buckets constantly +increase in size and number from the top +<span class='pagenum'><a name="Page_15" id="Page_15">[15]</a></span>toward the bottom. This is because the steam volume +increases progressively from the admission to the exhaust +and the entire expansion is carried out in the +separate sets of nozzles, very much as if it were one +continuous nozzle; but with this difference, not all of +the energy is taken out of the steam in any one set of +nozzles. The idea is to keep the velocity of the steam +in each stage as nearly constant as possible. The +nozzles in the diaphragms and the intermediates do +not, except in the lowest stage, take up the entire +circumference, but are proportioned to the progressive +expansion of steam as it descends toward the condenser.</p> + +<h3>Clearance</h3> + +<p>While the machine is running it is imperative that +there be no rubbing contact between the revolving +and stationary parts, and this is provided for by the +clearance between the rows of moving buckets and the +intermediates. Into each stage of the machine a +2-inch pipe hole is drilled and tapped. Sometimes this +<span class='pagenum'><a name="Page_16" id="Page_16">[16]</a></span>opening is made directly opposite a row of moving +buckets as in Fig. <a href="#FIG_10">10</a>, and sometimes it is made opposite +the intermediate. When opposite a row of buckets, +it will allow one to see the amount of clearance between +the buckets and the intermediates, and between the +buckets and the nozzles. When drilled opposite the +intermediates, the clearance is shown top and bottom +between the buckets and intermediates. (See Fig. <a href="#FIG_11">11</a>.) +This clearance is not the same in all stages, but is +greatest in the fourth stage and least in the first. The +clearances in each stage are nearly as follows: First +stage, 0.060 to 0.080; second stage, 0.080 to 0.100; +third stage, 0.080 to 0.100; fourth stage, 0.080 to +0.200. These clearances are measured by what are +called clearance gages, which are simply taper slips +of steel about 1/2-inch wide accurately ground and +graduated, like a jeweler's ring gage, by marks about +1/2-inch apart; the difference in thickness of the gage is +one-thousandth of an inch from one mark to the next.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_10" name="FIG_10"></a> + <a href="images/i016H.png"> + <img src="images/i016.png" + alt="FIG. 10" + title="FIG. 10" + /> + </a><br /> +FIG. 10</p> +</div> +<p><span class='pagenum'><a name="Page_17" id="Page_17">[17]</a></span></p> + +<div class="center"> +<p class="caption"> + <a id="FIG_11" name="FIG_11"></a> + <a href="images/i017H.png"> + <img src="images/i017.png" + alt="FIG. 11" + title="FIG. 11" + /> + </a><br /> +FIG. 11</p> +</div> + +<p>To determine whether the clearance is right, one of +the 2-inch plugs is taken out and some marking material, +such as red lead or anything that would be used +on a surface plate or bearing to mark the high spots +is rubbed on the taper gage, and it is pushed into the +gap between the buckets and intermediates as far as it +will go, and then pulled out, the marking on the gage +showing just how far in it went, and the nearest mark +giving in thousandths of an inch the clearance. This +is noted, the marking spread again, and the gage tried +on the other side, the difference on the gage showing +<span class='pagenum'><a name="Page_18" id="Page_18">[18]</a></span>whether the wheel is high or low. Whichever may be +the case the hight is corrected by the step-bearing +screw. The wheels should be placed as nearly in the +middle of the clearance space as possible. By some +operators the clearance is adjusted while running, in +the following manner: With the machine running at +full speed the step-bearing screw is turned until the +wheels are felt or heard to rub lightly. The screw is +marked and then turned in the opposite direction +until the wheel rubs again. Another mark is made +on the screw and it is then turned back midway +between the two marks. Either method is safe if practiced +by a skilful engineer. In measuring the clearance +by the first method, the gage should be used with +care, as it is possible by using too much pressure to +swing the buckets and get readings which could be +misleading. To an inexperienced man the taper +gages would seem preferable. In the hands of a man +who knows what he is doing and how to do it, a tapered +pine stick will give as satisfactory results as the most +elaborate set of hardened and ground clearance gages.</p> + +<p>Referring back to Fig. <a href="#FIG_11">11</a>, at <i>A</i> is shown one of the +peep-holes opposite the intermediate in the third +stage wheel for the inspection of clearance. The taper +clearance gage is inserted through this hole both above +and below the intermediate, and the distance which +it enters registers the clearance on that side. This +sketch also shows plainly how the shrouding on the +buckets and the intermediates extends beyond the +sharp edges of the buckets, protecting them from +damage in case of slight rubbing. In a very few cases +<span class='pagenum'><a name="Page_19" id="Page_19">[19]</a></span>wheels have been known to warp to such an extent +from causes that were not discovered until too late, +that adjustment would not stop the rubbing. In such +cases the shrouding has been turned or faced off by +a cutting-off tool used through the peep-hole.</p> + + +<h3>Carbon Packing Used</h3> + +<p>Where the shaft passes through the upper head of +the wheel-case some provision must be made to prevent +steam from the first stage escaping. This is +provided for by carbon packing (Fig. <a href="#FIG_12">12</a>), which consists +of blocks of carbon in sets in a packing case bolted +to the top head of the wheel-case. There are three +sets of these blocks, and each set is made of two rings +of three segments each. One ring of segments breaks +joints with its mate in the case, and each set is separated +from the others by a flange in the case in which +it is held. In some cases the packing is kept from +turning by means of a link, one end of which is fastened +to the case and the other to the packing holder. Sometimes +light springs are used to hold the packing against +the shaft and in some the pressure of steam in the case +does this. There is a pipe, also shown in Fig. <a href="#FIG_12">12</a>, +leading from the main line to the packing case, the +pressure in the pipe being reduced. The space between +the two upper sets of rings is drained to the third +stage by means of a three-way cock, which keeps the +balance between the atmosphere and packing-case +pressure. The carbon rings are fitted to the shaft +with a slight clearance to start with, and very soon get +<span class='pagenum'><a name="Page_20" id="Page_20">[20]</a></span>a smooth finish, which is not only practically steam-tight +but frictionless.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_12" name="FIG_12"></a> + <img src="images/i020.png" + alt="FIG. 12" + title="FIG. 12" + /><br /> +FIG. 12</p> +</div> + +<p>The carbon ring shown in Fig. <a href="#FIG_12">12</a> is the older design. +The segments are held against the flat bearing surface +of the case by spiral springs set in brass ferrules. The +circle is held together by a bronze strap screwed and +<span class='pagenum'><a name="Page_22" id="Page_22">[22]</a></span> +drawn together at the ends by springs. Still other +springs press the straps against the surface upon +which the carbon bears, cutting off leaks through +joints and across horizontal surfaces of the carbon. +The whole ring is prevented from turning by a connecting-rod +which engages a pin in the hole, like those +provided for the springs.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_13" name="FIG_13"></a> +<span class='pagenum'><a name="Page_21" id="Page_21">[21]</a></span> + <a href="images/i021H.png"> + <img src="images/i021.png" + alt="FIG. 13" + title="FIG. 13" + /> + </a><br /> +FIG. 13</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_14" name="FIG_14"></a> + <img src="images/i023a.png" + alt="FIG. 14" + title="FIG. 14" + /><br /> +FIG. 14</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_15" name="FIG_15"></a> + <img src="images/i023b.png" + alt="FIG. 15" + title="FIG. 15" + /><br /> +FIG. 15</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_16" name="FIG_16"></a> + <img src="images/i024.png" + alt="FIG. 16" + title="FIG. 16" + /><br /> +FIG. 16</p> +</div> + + +<h3>The Safety-stop</h3> + +<p>There are several designs of safety-stop or speed-limit +devices used with these turbines, the simplest +being of the ring type shown in Fig. <a href="#FIG_13">13</a>. This consists +of a flat ring placed around the shaft between +the turbine and generator. The ring-type emergencies +are now all adjusted so that they normally run concentric +with the shaft, but weighted so that the center +of gravity is slightly displaced from the center. The +centrifugal strain due to this is balanced by helical +springs. But when the speed increases the centrifugal +force moves the ring into an eccentric position, when +it strikes a trigger and releases a weight which, falling, +closes the throttle and shuts off the steam supply. The +basic principle upon which all these stops are designed +is the same—the centrifugal force of a weight balanced +by a spring at normal speed. +Figs. <a href="#FIG_14">14</a>, <a href="#FIG_15">15</a>, and <a href="#FIG_16">16</a> +show three other types.</p> + + +<h3>The Mechanical Valve-Gear</h3> + +<p>Fig. <a href="#FIG_17">17</a> shows plainly the operation of the mechanical +valve-gear. The valves are located in the steam chests, +which are bolted to the top of the casing directly +<span class='pagenum'><a name="Page_23" id="Page_23">[23]</a></span>over the first sets of expansion nozzles. The chests, +two in number, are on opposite sides of the machine. +The valve-stems extend upward through ordinary +stuffing-boxes, and are attached to the notched cross-heads +by means of a threaded end which is prevented +<span class='pagenum'><a name="Page_24" id="Page_24">[24]</a></span>from screwing in or out by a compression nut on the +lower end of the cross-head. Each cross-head is actuated +by a pair of reciprocating pawls, or dogs (shown +more plainly in the enlarged view, Fig. <a href="#FIG_18">18</a>), one of +which opens the valve and the other closes it. The +several pairs of pawls are hung on a common shaft +which receives a rocking motion from a crank driven +from a worm and worm-wheel by the turbine shaft. +The cross-heads have notches milled in the side in +<span class='pagenum'><a name="Page_26" id="Page_26">[26]</a></span> +which the pawls engage to open or close the valve, +this engagement being determined by what are called +shield-plates, <i>A</i> (Fig. <a href="#FIG_18">18</a>), which are controlled by the +<span class='pagenum'><a name="Page_27" id="Page_27">[27]</a></span>governor. These plates are set, one a little ahead of +the other, to obtain successive opening or closing of +the valves. When more steam is required the shield +plate allows the proper pawl to fall into its notch in +the cross-head and lift the valve from its seat. If +less steam is wanted the shield-plate rises and allows +the lower pawl to close the valve on the down stroke.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_17" name="FIG_17"></a> +<span class='pagenum'><a name="Page_25" id="Page_25">[25]</a></span> + <a href="images/i025H.png"> + <img src="images/i025.png" + alt="FIG. 17" + title="FIG. 17" + /> + </a><br /> +FIG. 17</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_18" name="FIG_18"></a> + <a href="images/i026H.png"> + <img src="images/i026.png" + alt="FIG. 18" + title="FIG. 18" + /> + </a><br /> +FIG. 18</p> +</div> + +<p>The valves, as can easily be seen, are very simple +affairs, the steam pressure in the steam chest holding +the valve either open or shut until it is moved by the +pawl on the rock-shaft. The amount of travel on +the rock-shaft is fixed by the design, but the proportionate +travel above and below the horizontal is +controlled by the length of the connecting-rods from +the crank to the rock-shaft. There are besides the +mechanical valve-gear the electric and hydraulic, but +these will be left for a future article.</p> + + +<h3>The Governor</h3> + +<p>The speed of the machine is controlled by the automatic +opening and closing of the admission valves +under the control of a governor (Fig. <a href="#FIG_19">19</a>), of the spring-weighted +type attached directly to the top end of +the turbine shaft. The action of the governor depends +on the balance of force exerted by the spring, and +the centrifugal effort of the rectangular-shaped weights +at the lower end; the moving weights acting through +the knife-edge suspension tend to pull down the lever +against the resistance of the heavy helical spring. +The governor is provided with an auxiliary spring on +the outside of the governor dome for varying the speed +<span class='pagenum'><a name="Page_28" id="Page_28">[28]</a></span>while synchronizing. The tension of the auxiliary +spring is regulated by a small motor wired to the +switchboard. This spring should be used only to +correct slight changes in speed. Any marked change +should be corrected by the use of the large hexagonal +nut in the upper plate of the governor frame. This +nut is screwed down to increase the speed, and upward +to decrease it.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_19" name="FIG_19"></a> + <a href="images/i028H.png"> + <img src="images/i028.png" + alt="FIG. 19" + title="FIG. 19" + /> + </a><br /> +FIG. 19</p> +</div> + + +<h3>The Stage Valves</h3> + +<p>Fig. <a href="#FIG_20">20</a> represents one of the several designs of +stage valve, sometimes called the overload valve, +the office of which is to prevent too high pressure in +the first stage in case of a sudden overload, and to +<span class='pagenum'><a name="Page_29" id="Page_29">[29]</a></span>transfer a part of the steam to a special set of expanding +nozzles over the second-stage wheel. This valve +is balanced by a spring of adjustable tension, and is, +or can be, set to open and close within a very small +predetermined range of first-stage pressure. The +valve is <i>intended</i> to open and close instantly, and +to supply or cut off steam from the second stage, +without affecting the speed regulation or economy of +<span class='pagenum'><a name="Page_30" id="Page_30">[30]</a></span>operation. If any leaking occurs past the valve it +is taken care of by a drip-pipe to the third stage.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_20" name="FIG_20"></a> + <img src="images/i029.png" + alt="FIG. 20" + title="FIG. 20" + /><br /> +FIG. 20</p> +</div> + +<p>The steam which passes through the automatic +stage valves and is admitted to the extra set of nozzles +above the second-stage wheel acts upon this wheel +just the same as the steam which passes through the +regular second-stage nozzles; <i>i.e.</i>, all the steam which +goes through the machine tends to hasten its speed, +or, more accurately, does work and <i>maintains</i> the speed +of the machine.</p> + + + +<hr class="major" /><p><span class='pagenum'><a name="Page_31" id="Page_31">[31]</a></span></p> +<h2><a name="II_SETTING_THE_VALVES_OF_THE_CURTIS_TURBINE2" id="II_SETTING_THE_VALVES_OF_THE_CURTIS_TURBINE2"></a>II. SETTING THE VALVES OF THE CURTIS TURBINE<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a></h2> + + +<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> Contributed to <i>Power</i> by F. L. Johnson.</p></div> + +<p><span class="smcap">Under</span> some conditions of service the stage valve +in the Curtis turbine will not do what it is designed +to do. It is usually attached to the machine in such +manner that it will operate with, or a little behind, +in the matter of time, the sixth valve. The machine +is intended to carry full load with only the first bank +of five valves in operation, with proper steam pressure +and vacuum. If the steam pressure is under 150 +pounds, or the vacuum is less than 28 inches, the sixth +valve may operate at or near full load, and also open +the stage valve and allow steam to pass to the second-stage +nozzles at a much higher rate of speed than the +steam which has already done some work in the first-stage +wheel. The tendency is to accelerate unduly +the speed of the machine. This is corrected by the +governor, but the correction is usually carried too far +and the machine slows down. With the stage valve +in operation, at a critical point the regulation is uncertain +and irregular, and its use has to be abandoned. +The excess first-stage pressure will then be taken care +of by the relief valve, which is an ordinary spring +<span class='pagenum'><a name="Page_32" id="Page_32">[32]</a></span>safety valve (not pop) which allows the steam to +blow into the atmosphere.</p> + +<p>The mechanical valve-gear does not often get out +of order, but sometimes the unexpected happens. The +shop man may not have properly set up the nuts on +the valve-stems; or may have fitted the distance bushings +between the shield plates too closely; the superheat +of the steam may distort the steam chest slightly +and produce friction that will interfere with the regulation. +If any of the valve-stems should become loose +in the cross-heads they may screw themselves either +in or out. If screwed out too far, the valve-stem +becomes too long and the pawl in descending will, +after the valve is seated, continue downward until it +has broken something. If screwed in, the cross-head +will be too low for the upper pawl to engage and the +valve will not be opened. This second condition is +not dangerous, but should be corrected. The valve-stems +should be made the right length, and all check-nuts +set up firmly. If for any purpose it becomes +necessary to "set the valves" on a 1500-kilowatt +mechanical gear, the operator should proceed in the +following manner.</p> + + +<h3>Setting the Valves of a 1500-Kilowatt Curtis Turbine</h3> + +<p>We will consider what is known as the "mechanical" +valve-gear, with two sets of valves, one set of five +valves being located on each side of the machine.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_21" name="FIG_21"></a> + <img src="images/i033.png" + alt="FIG. 21" + title="FIG. 21" + /><br /> +FIG. 21</p> +</div> + +<p>In setting the valves we should first "throw out" all +pawls to avoid breakage in case the rods are not already +<span class='pagenum'><a name="Page_33" id="Page_33">[33]</a></span>of proper length, holding the pawls out by slipping the +ends of the pawl springs over the points of the pawls, +as seen in Fig. <a href="#FIG_21">21</a>. Then turn the machine slowly by +hand until the pawls on one set of valves are at their +highest point of travel, then with the valves wide +open adjust the drive-rods, <i>i.e.</i>, the rods extending +from the crank to the rock-shaft, so that there is 1/32 +of an inch clearance (shown dotted in Fig. <a href="#FIG_17">17</a>, Chap. I) +at the point of opening of the pawls when they are +"in." (See Fig. <a href="#FIG_22">22</a>.) Then set up the check-nuts +on the drive-rod. Turn the machine slowly, until the +pawls are at their lowest point of travel. Then, with +the valves closed, adjust each <i>valve-stem</i> to give 1/32 +of an inch clearance at the point of closing of the +pawls when they are "in," securely locking the check-nut +as each valve is set. Repeat this operation on +the other side of the machine and we are ready to +<span class='pagenum'><a name="Page_34" id="Page_34">[34]</a></span> +adjust the governor-rods. (Valves cannot be set on +both sides of the machine at the same time, as the +pawls will not be in the same relative position, due to +the angularity of the drive-rods.)</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_22" name="FIG_22"></a> +<span class='pagenum'><a name="Page_35" id="Page_35">[35]</a></span> + <a href="images/i034H.png"> + <img src="images/i034.png" + alt="FIG. 22" + title="FIG. 22" + /> + </a><br /> +FIG. 22</p> +</div> + +<p>Next, with the turbine running, and the synchronizing +spring in mid-position, adjust the governor-rods +so that the turbine will run at the normal speed of +900 revolutions per minute when working on the fifth +valve, and carrying full load. The governor-rods for +the other side of the turbine (controlling valves Nos. 6 +to 10) should be so adjusted that the speed change +between the fifth and sixth valves will not be more +than three or four revolutions per minute.</p> + +<p>The valves of these turbines are all set during the +shop test and the rods trammed with an 8-inch tram. +Governors are adjusted for a speed range of 2 per +cent. between no load and full load (1500 kilowatt), +or 4 per cent. between the mean speeds of the first +and tenth valves (no load to full overload capacity).</p> + +<p>The rods which connect the governor with the valve-gear +have ordinary brass ends or heads and are +adjusted by right-and-left threads and secured by lock-nuts. +They are free fits on the pins which pass through +the heads, and no friction is likely to occur which will +interfere with the regulation, but too close work on +the shield-plate bushings, or a slight warping of the +steam chest, will often produce friction which will +seriously impair the regulation. If it is noticed that +the shield-plate shaft has any tendency to oscillate +in unison with the rock-shaft which carries the pawls, +it is a sure indication that the shield-plates are not as +<span class='pagenum'><a name="Page_36" id="Page_36">[36]</a></span>free as they should be, and should be attended to. +The governor-rod should be disconnected, the pawls +thrown out and the pawl strings hooked over the ends.</p> + +<p>The plates should then be rocked up and down by +hand and the friction at different points noted. The +horizontal rod at the back of the valve-gear may be +loosened and the amount of end play of each individual +shield-plate noticed and compared with the bushings +on the horizontal rod at the back which binds the +shield-plates together. If the plates separately are +found to be perfectly free they may be each one pushed +hard over to the right or left and wedged; then each +bushing tried in the space between the tail-pieces of +the plates. It will probably be found that the bushings +are not of the right length, due to the alteration +of the form of the steam chest by heat. It will generally +be found also that the bushings are too short, +and that the length can be corrected by very thin +washers of sheet metal. It has been found in some +instances that the thin bands coming with sectional +pipe covering were of the right thickness.</p> + +<p>After the length of the bushings is corrected the +shield-plates may be assembled, made fast and tested +by rocking them up and down, searching for signs of +sticking. If none occurs, the work has been correctly +done, and there will be no trouble from poor regulation +due to friction of the shield-plates.</p> + + +<h3>The Baffler</h3> + +<p>The water which goes to the step-bearing passes +through a baffler, the latest type of which is shown by +<span class='pagenum'><a name="Page_37" id="Page_37">[37]</a></span>Fig. <a href="#FIG_23">23</a>. It is a device for restricting the flow of water +or oil to the step- and guide-bearing. The amount +of water necessary to float the machine and lubricate +the guide-bearing having been determined by calculation +and experiment, the plug is set at that point +which will give the desired flow. The plug is a square-threaded +worm, the length of which and the distance +which it enters the barrel of the baffler determining +the amount of flow. The greater the number of turns +which the water must pass through in the worm the +less will flow against the step-pressure.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_23" name="FIG_23"></a> + <img src="images/i037.png" + alt="FIG. 23" + title="FIG. 23" + /><br /> +FIG. 23</p> +</div> + +<p><span class='pagenum'><a name="Page_38" id="Page_38">[38]</a></span>The engineers who have settled upon the flow and +the pressure decided that a flow of from 4-1/2 to 5-1/2 +gallons per minute and a step-pressure of from 425 +to 450 pounds is correct. These factors are so dependent +upon each other and upon the conditions of +the step-bearing itself that they are sometimes difficult +to realize in every-day work; nor is it necessary. +If the machine turns freely with a lower pressure than +that prescribed by the engineers, there is no reason +for raising this pressure; and there is only one way of +doing it without reducing the area of the step-bearing, +and that is by obstructing the flow of water in the +step-bearing itself.</p> + +<p>A very common method used is that of grinding. +The machine is run at about one-third speed and the +step-water shut off for 15 or 20 seconds. This causes +grooves and ridges on the faces of the step-bearing +blocks, due to their grinding on each other, which +obstruct the flow of water between the faces and thus +raises the pressure. It seems a brutal way of getting +a scientific result, if the result desired can be called +scientific. The grooving and cutting of the step-blocks +will not do any harm, and in fact they will aid +in keeping the revolving parts of the machine turning +about its mechanical center.</p> + +<p>The operating engineer will be very slow to see the +utility of the baffler, and when he learns, as he will +sometime, that the turbine will operate equally well +with a plug out as with it in the baffler, he will be inclined +to remove the baffler. It is true that with +one machine operating on its own pump it is possible +<span class='pagenum'><a name="Page_39" id="Page_39">[39]</a></span>to run without the baffler, and it is also possible that +in some particular case two machines having identical +step-bearing pressures might be so operated. The +baffler, however, serves a very important function, as +described more fully as follows: It tends to steady +the flow from the pump, to maintain a constant oil +film as the pressure varies with the load, and when +several machines are operating on the same step-bearing +system it is the only means which fixes the flow to +the different machines and prevents one machine from +robbing the others. Therefore, even if an engineer +felt inclined to remove the baffler he would be most +liable to regret taking such a step.</p> + +<p>If the water supply should fail from any cause and +the step-bearing blocks rub together, no great amount +of damage will result. The machine will stop if operated +long under these conditions, for if steam pressure +is maintained the machine will continue in operation +until the buckets come into contact, and if the step-blocks +are not welded together the machine may be +started as soon as the water is obtained. If vibration +occurs it will probably be due to the rough treatment +of the step-blocks, and may be cured by homeopathic +repeat-doses of grinding, say about 15 seconds each. +If the step-blocks are welded a new pair should be +substituted and the damaged ones refaced.</p> + +<p>Some few experimental steps of spherical form, +called "saucer" steps, have been installed with success +(see Fig. <a href="#FIG_24">24</a>). They seem to aid the lower guide-bearing +in keeping the machine rotating about the +mechanical center and reduce the wear on the guide-bearing. +<span class='pagenum'><a name="Page_40" id="Page_40">[40]</a></span>In some instances, too, cast-iron bushings +have been substituted for bronze, with marked success. +There seems to be much less wear between +cast-iron and babbitt metal than between bronze and +babbitt metal. The matter is really worth a thorough +investigation.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_24" name="FIG_24"></a> + <img src="images/i040.png" + alt="FIG. 24" + title="FIG. 24" + /><br /> +FIG. 24</p> +</div> + + + +<hr class="major" /><p><span class='pagenum'><a name="Page_41" id="Page_41">[41]</a></span></p> +<h2><a name="III_ALLIS-CHALMERS_COMPANY_STEAM_TURBINE" id="III_ALLIS-CHALMERS_COMPANY_STEAM_TURBINE"></a>III. ALLIS-CHALMERS COMPANY STEAM TURBINE</h2> + + +<p><span class="smcap">In</span> Fig. <a href="#FIG_25">25</a> may be seen the interior construction of +the steam turbine built by Allis-Chalmers Co., of Milwaukee, +Wis., which is, in general, the same as the +well-known Parsons type. This is a plan view showing +the rotor resting in position in the lower half of its casing.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_25" name="FIG_25"></a> + <a href="images/i041H.png"> + <img src="images/i041.png" + alt="FIG. 25" + title="FIG. 25" + /> + </a><br /> +FIG. 25</p> +</div> + +<p>Fig. <a href="#FIG_26">26</a> is a longitudinal cross-section cut of rotor +and both lower and upper casing. Referring to Fig. <a href="#FIG_26">26</a> +the steam comes in from the steam-pipe at <i>C</i> and +passes through the main throttle or regulating valve +<i>D</i>, which is a balanced valve operated by the governor. +Steam enters the cylinder through the passage <i>E</i>.</p> + +<p>Turning in the direction of the bearing <i>A</i>, it passes +through alternate stationary and revolving rows of +<span class='pagenum'><a name="Page_42" id="Page_42">[42]</a></span>blades, finally emerging at <i>F</i> and going out by way of +<i>G</i> to the condenser or to atmosphere. <i>H</i>, <i>J</i>, and <i>K</i> +represent three stages of blading. <i>L</i>, <i>M</i>, and <i>Z</i> are +the balance pistons which counterbalance the thrust +on the stages <i>H</i>, <i>J</i>, and <i>K</i>. <i>O</i> and <i>Q</i> are equalizing +pipes, and for the low-pressure balance piston similar +provision is made by means of passages (not shown) +through the body of the spindle.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_26" name="FIG_26"></a> + <a href="images/i042H.png"> + <img src="images/i042.png" + alt="FIG. 26" + title="FIG. 26" + /> + </a><br /> +FIG. 26</p> +</div> + +<p><i>R</i> indicates a small adjustable collar placed inside +the housing of the main bearing <i>B</i> to hold the spindle +in a position where there will be such a clearance +between the rings of the balance pistons and those of +the cylinder as to reduce the leakage of steam to a +minimum and at the same time prevent actual contact +under varying temperature.</p> + +<p>At <i>S</i> and <i>T</i> are glands which provide a water seal +against the inleakage of air and the outleakage of +steam. <i>U</i> represents the flexible coupling to the +generator. <i>V</i> is the overload or by-pass valve used +for admitting steam to intermediate stage of the turbine. +<span class='pagenum'><a name="Page_43" id="Page_43">[43]</a></span><i>W</i> is the supplementary cylinder to contain +the low-pressure balance piston. <i>X</i> and <i>Y</i> are reference +letters used in text of this chapter to refer to +equalizing of steam pressure on the low-pressure +stage of the turbine. The first point to study in this +construction is the arrangement of "dummies" <i>L</i>, <i>M</i>, +and <i>Z</i>. These dummy rings serve as baffles to prevent +steam leakage past the pistons, and their contact +at high velocity means not only their own destruction, +but also damage to or the wrecking of surrounding +parts. A simple but effective method of eliminating +this difficulty is found in the arrangement illustrated +in this figure. The two smaller balance pistons, <i>L</i> +and <i>M</i>, are allowed to remain on the high-pressure +end; but the largest piston, <i>Z</i>, is placed upon the +low-pressure end of the rotor immediately behind the +last ring of blades, and working inside of the supplementary +cylinder <i>W</i>. Being backed up by the body of +the spindle, there is ample stiffness to prevent warping. +This balance piston, which may also be plainly +seen in Fig. <a href="#FIG_25">25</a>, receives its steam pressure from the +same point as the piston <i>M</i>, but the steam pressure, +equalized with that on the third stage of the blading, +<i>X</i>, is through holes in the webs of the blade-carrying +rings. Entrance to these holes is through the small +annular opening in the rotor, visible in Fig. <a href="#FIG_25">25</a> between +the second and third barrels. As, in consequence of +varying temperatures, there is an appreciable difference +in the endwise expansion of the spindle and cylinder, +the baffling rings in the low-pressure balance +piston are so made as to allow for this difference. +<span class='pagenum'><a name="Page_44" id="Page_44">[44]</a></span>The high-pressure end of the spindle being held by +the collar bearing, the difference in expansion manifests +itself at the low-pressure end. The labyrinth +packing of the high-pressure and intermediate pistons +has a small axial and large radial clearance, +whereas the labyrinth packing of the piston <i>Z</i> has, +vice versa, a small radial and large axial clearance. +Elimination of causes of trouble with the low-pressure +balance piston not only makes it possible to +reduce the diameter of the cylinder, and prevent distortion, +but enables the entire spindle to be run with +sufficiently small clearance to obviate any excessive +leakage of steam.</p> + + +<h3>Detail of Blade Construction</h3> + +<p>In this construction the blades are cut from drawn +stock, so that at its root it is of angular dovetail shape, +while at its tip there is a projection. To hold the +roots of the blades firmly, a foundation ring is provided, +as shown at <i>A</i> in Fig. <a href="#FIG_27">27</a>. This foundation +ring is first formed to a circle of the proper diameter, +and then slots are cut in it. These slots are accurately +spaced and inclined to give the right pitch and angle +to the blades (Fig. <a href="#FIG_28">28</a>), and are of dovetail shape to +receive the roots of the blades. The tips of the blades +are substantially bound together and protected by +means of a channel-shaped shroud ring, illustrated in +Fig. <a href="#FIG_31">31</a> and at <i>B</i> in Fig. <a href="#FIG_27">27</a>. Fig. <a href="#FIG_31">31</a> shows the cylinder +blading separate, and Fig. <a href="#FIG_27">27</a> shows both with the +shrouding. In these, holes are punched to receive +<span class='pagenum'><a name="Page_45" id="Page_45">[45]</a></span> +the projections on the tips of the blades, which are +rivetted over pneumatically.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_27" name="FIG_27"></a> +<span class='pagenum'><a name="Page_46" id="Page_46">[46]</a></span> + <img src="images/i045.png" + alt="FIG. 27" + title="FIG. 27" + /><br /> +FIG. 27</p> +</div> + +<p>The foundation rings themselves are of dovetail +shape in cross-section, and, after receiving the roots +of the blades, are inserted in dovetailed grooves in +the cylinder and rotor, where they are firmly held in +place by keypieces, as may be seen at <i>C</i> in Fig. <a href="#FIG_27">27</a>. +Each keypiece, when driven in place, is upset into +an undercut groove, indicated by <i>D</i> in Fig. <a href="#FIG_27">27</a>, thereby +positively locking the whole structure together. Each +separate blade is firmly secured by the dovetail shape +of the root, which is held between the corresponding +dovetailed slot in the foundation ring and the undercut +side of the groove.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_28" name="FIG_28"></a> + <img src="images/i046.png" + alt="FIG. 28" + title="FIG. 28" + /><br /> +FIG. 28</p> +</div> + +<p>Fig. <a href="#FIG_29">29</a>, from a photograph of blading fitted in a +turbine, illustrates the construction, besides showing +the uniform spacing and angles of the blades.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_29" name="FIG_29"></a> + <a href="images/i047H.png"> + <img src="images/i047.png" + alt="FIG. 29" + title="FIG. 29" + /> + </a><br /> +FIG. 29</p> +</div> + +<p>The obviously thin flanges of the shroud rings are +purposely made in that way, so that, in case of accidental +contact between revolving and stationary +parts, they will wear away enough to prevent the +<span class='pagenum'><a name="Page_47" id="Page_47">[47]</a></span> +blades from being ripped out. This protection, however, +is such that to rip them out a whole half ring +of blades must be sheared off at the roots. The +strength of the blading, therefore, depends not upon +the strength of an individual blade, but upon the combined +shearing strength of an entire ring of blades.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_30" name="FIG_30"></a> +<span class='pagenum'><a name="Page_48" id="Page_48">[48]</a></span> + <a href="images/i048H.png"> + <img src="images/i048.png" + alt="FIG. 30" + title="FIG. 30" + /> + </a><br /> +FIG. 30</p> +</div> + +<p>The blading is made up and inserted in half rings, +and Fig. <a href="#FIG_30">30</a> shows two rings of different sizes ready to +be put in place. Fig. <a href="#FIG_31">31</a> shows a number of rows of +blading inserted in the cylinder of an Allis-Chalmers +steam turbine, and Fig. <a href="#FIG_32">32</a> gives view of blading in +the same turbine after nearly three years' running.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_31" name="FIG_31"></a> + <a href="images/i049H.png"> + <img src="images/i049.png" + alt="FIG. 31" + title="FIG. 31" + /> + </a><br /> +FIG. 31</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_32" name="FIG_32"></a> + <a href="images/i050H.png"> + <img src="images/i050.png" + alt="FIG. 32" + title="FIG. 32" + /> + </a><br /> +FIG. 32</p> +</div> + + +<h3>The Governor</h3> + +<p>Next in importance to the difference in blading and +balance piston construction, is the governing mechanism +<span class='pagenum'><a name="Page_49" id="Page_49">[49]</a></span>used with these machines. This follows the well-known +Hartung type, which has been brought into +prominence, heretofore largely in connection with +hydraulic turbines; and the governor, driven directly +from the turbine shaft by means of cut gears working +in an oil bath, is required to operate the small, balanced +oil relay-valve only, while the two steam valves, +main and by-pass (or overload), are controlled by an +<span class='pagenum'><a name="Page_50" id="Page_50">[50]</a></span>oil pressure of about 20 pounds per square inch, acting +upon a piston of suitable size. In view of the fact +that a turbine by-pass valve opens only when the +unit is required to develop overload, or the vacuum +fails, a good feature of this governing mechanism is +that the valve referred to can be kept constantly in +motion, thereby preventing sticking in an emergency, +even though it be actually called into action +only at long intervals. Another feature of importance +<span class='pagenum'><a name="Page_51" id="Page_51">[51]</a></span>is that the oil supply to the bearings, as well as +that to the governor, can be interconnected so that +the governor will automatically shut off the steam if +the oil supply fails and endangers the bearings. This +mechanism is also so proportioned that, while responding +quickly to variations in load, its sensitiveness is +kept within such bounds as to secure the best results +in the parallel operation of alternators. The governor +can be adjusted for speed while the turbine is in +operation, thereby facilitating the synchronizing of +alternators and dividing the load as may be desired.</p> + +<p>In order to provide for any possible accidental derangement +of the main governing mechanism, an +entirely separate safety or over-speed governor is +furnished. This governor is driven directly by the +turbine shaft without the intervention of gearing, and +is so arranged and adjusted that, if the turbine should +reach a predetermined speed above that for which the +main governor is set, the safety governor will come +into action and trip a valve which entirely shuts off +the steam supply, bringing the turbine to a stop.</p> + + +<h3>Lubrication</h3> + +<p>Lubrication of the four bearings, which are of the +self-adjusting, ball and socket pattern, is effected by +supplying an abundance of oil to the middle of each +bearing and allowing it to flow out at the ends. The +oil is passed through a tubular cooler, having water +circulation, and pumped back to the bearings. Fig. +<a href="#FIG_33">33</a> shows the entire arrangement graphically and +much more clearly than can be explained in words. +<span class='pagenum'><a name="Page_53" id="Page_53">[53]</a></span> +The oil is circulated by a pump directly operated +from the turbine, except where the power-house is +provided with a central oiling system. Particular +stress is laid by the builders upon the fact that it is +not necessary to supply the bearings with oil under +pressure, but only at a head sufficient to enable it to +run to and through the bearings; this head never +exceeding a few feet. With each turbine is installed +a separate direct-acting steam pump for circulating +oil for starting up. This will be referred to again +under the head of operating.</p> + +<div class="center"> +<p class="caption"> +<span class='pagenum'><a name="Page_52" id="Page_52">[52]</a></span> + <a id="FIG_33" name="FIG_33"></a> + <a href="images/i052H.png"> + <img src="images/i052.png" + alt="FIG. 33" + title="FIG. 33" + /> + </a><br /> +FIG. 33</p> +</div> + + +<h3>Generator</h3> + +<p>The turbo-generator, which constitutes the electrical +end of this unit, is totally enclosed to provide +for noiseless operation, and forced ventilation is secured +by means of a small fan carried by the shaft on +each end of the rotor. The air is taken in at the ends +of the generator, passes through the fans and is discharged +over the end connections of the armature +coils into the bottom of the machine, whence it passes +through the ventilating ducts of the core to an opening +at the top. The field core is, according to size, +built up either of steel disks, each in one piece, or of +steel forgings, so as to give high magnetic permeability +and great strength. The coils are placed in radial +slots, thereby avoiding side pressure on the slot insulation +and the complex stresses resulting from centrifugal +force, which, in these rotors, acts normal to +the flat surface of the strip windings.</p><p><span class='pagenum'><a name="Page_54" id="Page_54">[54]</a></span></p> + + +<h3>Operation</h3> + +<p>As practically no adjustments are necessary when +these units are in operation, the greater part of the +attention required by them is involved in starting up +and shutting down, which may be described in detail +as follows:</p> + +<p><i>To Start Up</i></p> + +<p>First, the auxiliary oil pump is set going, and this +is speeded up until the oil pressure shows a hight +sufficient to lift the inlet valve and oil is flowing steadily +at the vents on all bearings. The oil pressure then +shows about 20 to 25 pounds on the "Relay Oil" +gage, and 2 to 4 pounds on the "Bearing Oil" gage. +Next the throttle is opened, without admitting sufficient +steam to the turbine to cause the spindle to +turn, and it is seen that the steam exhausts freely +into the atmosphere, also that the high-pressure end +of the turbine expands freely in its guides. Water +having been allowed to blow out through the steam-chest +drains, the drains are closed and steam is permitted +to continue flowing through the turbine not +less than a half an hour (unless the turbine is warm +to start with, when this period may be reduced) still +without turning the spindle. After this it is advisable +to shut off steam and let the turbine stand ten minutes, +so as to warm thoroughly, during which time +the governor parts may be oiled and any air which +may have accumulated in the oil cylinder above the +inlet valve blown off. Then the throttle should be +opened sufficiently to start the turbine spindle to revolving +<span class='pagenum'><a name="Page_55" id="Page_55">[55]</a></span>very slowly and the machine allowed to run in +this way for five minutes.</p> + +<p>Successive operations may be mentioned briefly as +admitting water to the oil cooler; bringing the turbine +up to speed, at the same time slowing down the auxiliary +oil pump and watching that the oil pressures +are kept up by the rotary oil pump on the turbine; +turning the water on to the glands very gradually +and, before putting on vacuum, making sure that +there is just enough water to seal these glands properly; +and starting the vacuum gradually just before +putting on the load. These conditions having been +complied with, the operator next turns his attention +to the generator, putting on the field current, synchronizing +carefully and building up the load on the +unit gradually.</p> + +<p>The principal precautions to be observed are not +to start without warming up properly, to make sure +that oil is flowing freely through the bearings, that +vacuum is not put on until the water glands seal, and +to avoid running on vacuum without load on the +turbine.</p> + + +<h3>In Operation</h3> + +<p>In operation all that is necessary is to watch the +steam pressure at the "Throttle" and "Inlet" gages, +to see that neither this pressure nor the steam temperature +varies much; to keep the vacuum constant, +as well as pressures on the water glands and those +indicated by the "Relay Oil" and "Bearing Oil" +gages; to take care that the temperatures of the oil +<span class='pagenum'><a name="Page_56" id="Page_56">[56]</a></span>flowing to and from the bearings does not exceed +135 degrees Fahr. (at which temperature the hand +can comfortably grasp the copper oil-return pipes); +to see that oil flows freely at all vents on the bearings, +and that the governor parts are periodically oiled. +So far as the generator is concerned, it is only essential +to follow the practice common in all electric power +plant operation, which need not be reviewed here.</p> + +<p><i>Stopping the turbine</i> is practically the reverse of +starting, the successive steps being as follows: starting +the auxiliary oil pump, freeing it of water and allowing +it to run slowly; removing the load gradually; +breaking the vacuum when the load is almost zero, +shutting off the condenser injection and taking care +that the steam exhausts freely into the atmosphere; +shutting off the gland water when the load and vacuum +are off; pulling the automatic stop to trip the +valve and shut off steam and, as the speed of the +turbine decreases, speeding up the auxiliary oil pump +to maintain pressure on the bearings; then, when the +turbine has stopped, shutting down the auxiliary oil +pump, turning off the cooling water, opening the steam +chest drains and slightly oiling the oil inlet valve-stem. +During these operations the chief particulars +to be heeded are: not to shut off the steam before +starting the auxiliary oil pump nor before the vacuum +is broken, and not to shut off the gland water with +vacuum on the turbine. The automatic stop should +also remain unhooked until the turbine is about to +be started up again.</p><p><span class='pagenum'><a name="Page_57" id="Page_57">[57]</a></span></p> + + +<h3>General</h3> + +<p>Water used in the glands of the turbine must be +free from scale-forming impurities and should be +delivered at the turbine under a steady pressure of +not less than 15 pounds. The pressure in the glands +will vary from 4 to 10 pounds. This water may be +warm. In the use of water for the cooling coils and +of oil for the lubricating system, nothing more is +required than ordinary good sense dictates. An absolutely +pure mineral oil must be supplied, of a non-foaming +character, and it should be kept free through +filtering from any impurities.</p> + +<p>The above refers particularly to Allis-Chalmers +turbines of the type ordinarily used for power service. +For turbines built to be run non-condensing, the part +relating to vacuum does not, of course, apply.</p> + + + +<hr class="major" /><p><span class='pagenum'><a name="Page_58" id="Page_58">[58]</a></span></p> +<h2><a name="IV_WESTINGHOUSE-PARSONS_STEAM_TURBINE" id="IV_WESTINGHOUSE-PARSONS_STEAM_TURBINE"></a>IV. WESTINGHOUSE-PARSONS STEAM TURBINE</h2> + + +<p><span class="smcap">While</span> the steam turbine is simple in design and +construction and does not require constant tinkering +and adjustment of valve gears or taking up of wear +in the running parts, it is like any other piece of fine +machinery in that it should receive intelligent and +careful attention from the operator by inspection of +the working parts that are not at all times in plain +view. Any piece of machinery, no matter how simple +and durable, if neglected or abused will in time come +to grief, and the higher the class of the machine the +more is this true.</p> + +<p>Any engineer who is capable of running and intelligently +taking care of a reciprocating engine can run +and take care of a turbine, but if he is to be anything +more than a starter and stopper, it is necessary that +he should know what is inside of the casing, what must +be done and avoided to prevent derangement, and to +keep the machine in continued and efficient operation.</p> + +<p>In the steam turbine the steam instead of being +expanded against a piston is made to expand against +and to get up velocity in itself. The jet of steam is +then made to impinge against vanes or to react against +the moving orifice from which it issues, in either of +<span class='pagenum'><a name="Page_59" id="Page_59">[59]</a></span>which cases its velocity and energy are more or less +completely abstracted and appropriated by the revolving +member. The Parsons turbine utilizes a +combination of these two methods.</p> +<p><span class='pagenum'><a name="Page_60" id="Page_60">[60]</a></span></p> + +<div class="center"> +<p class="caption"> + <a id="FIG_34" name="FIG_34"></a> + <a href="images/i060H.png"> + <img src="images/i060.png" + alt="FIG. 34" + title="FIG. 34" + /> + </a><br /> +FIG. 34</p> +</div> + +<p>Fig. <a href="#FIG_34">34</a> is a sectional view of the standard Westinghouse-Parsons +single-flow turbine. A photograph of +the rotor <i>R R R</i> is reproduced in Fig. <a href="#FIG_35">35</a>, while in Fig. +<a href="#FIG_36">36</a> a section of the blading is shown upon a larger +scale. Between the rows of the blading upon the +rotor extend similar rows of stationary blades attached +to the casing or stator. The steam entering at <i>A</i> +(Fig. <a href="#FIG_34">34</a>), fills the circular space surrounding the rotor +and passes first through a row of stationary blades, 1 +(Fig. <a href="#FIG_37">37</a>), expanding from the initial pressure <i>P</i> to +the slightly lower pressure <i>P</i><span class="sub">1</span>, and attaining by that +expansion a velocity with which it is directed upon +the moving blade 2. In passing through this row of +blades it is further expanded from pressure <i>P</i><span class="sub">1</span> to <i>P</i><span class="sub">2</span> +and helps to push the moving blades along by the reaction +of the force with which it issues therefrom. Impinging +upon the second row of stationary blades 3, +the direction of flow is diverted so as to make it impinge +at a favorable angle upon the second row of +revolving blades 4, and the action is continued until +the steam is expanded to the pressure of the condenser +or of the medium into which the turbine finally +exhausts. As the expansion proceeds, the passages +are made larger by increasing the length of the blades +and the diameter of the drums upon which they are +carried in order to accommodate the increasing volume.</p> + + +<div class="center"> +<p class="caption"> + <a id="FIG_35" name="FIG_35"></a> +<span class='pagenum'><a name="Page_61" id="Page_61">[61]</a></span> + <a href="images/i061H.png"> + <img src="images/i061.png" + alt="FIG. 35" + title="FIG. 35" + /> + </a><br /> +FIG. 35</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_36" name="FIG_36"></a> +<span class='pagenum'><a name="Page_62" id="Page_62">[62]</a></span> + <a href="images/i062H.png"> + <img src="images/i062.png" + alt="FIG. 36" + title="FIG. 36" + /> + </a><br /> +FIG. 36</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_37" name="FIG_37"></a> +<span class='pagenum'><a name="Page_63" id="Page_63">[63]</a></span> + <img src="images/i063.png" + alt="FIG. 37" + title="FIG. 37" + /><br /> +FIG. 37</p> +</div> + +<p>It is not necessary that the blades shall run close +together, and the axial clearance, that is the space +lengthwise of the turbine between the revolving and +the stationary blades, varies from 1/8 to 1/2 inch; but in +order that there may not be excessive leakage over +the tops of the blades, as shown, very much exaggerated, +in Fig. <a href="#FIG_38">38</a>, the radial clearance, that is, the clearance +between the tops of the moving blades and the +casing, and between the ends of the stationary blades +and the shell of the rotor, must be kept down to the +lowest practical amount, and varies, according to the +size of the machine and length of blade, from about +0.025 to 0.125 of an inch.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_38" name="FIG_38"></a> + <a href="images/i064H.png"> + <img src="images/i064.png" + alt="FIG. 38" + title="FIG. 38" + /> + </a><br /> +FIG. 38</p> +</div> + +<p>In the passage <i>A</i> (Fig. <a href="#FIG_34">34</a>) exists the initial pressure; +in the passage <i>B</i> the pressure after the steam +has passed the first section or diameter of the rotor; +in the passage <i>C</i> after it has passed the second section. +The pressure acting upon the exposed faces +of the rows of vanes would crowd the rotor to the +left. They are therefore balanced by pistons or +"dummies" <i>P P P</i> revolving with the shaft and exposing +in the annular spaces <i>B</i><span class="sup">1</span> and <i>C</i><span class="sup">1</span> the same areas +<span class='pagenum'><a name="Page_64" id="Page_64">[64]</a></span>as those of the blade sections which they are designed +to balance. The same pressure is maintained in <i>B</i><span class="sup">1</span> +as in <i>B</i>, and in <i>C</i><span class="sup">1</span> as in <i>C</i> by connecting them with +equalizing pipes <i>E E</i>. The third equalizing pipe +<span class='pagenum'><a name="Page_65" id="Page_65">[65]</a></span>connects the back or right-hand side of the largest dummy +with the exhaust passage so that the same pressure +exists upon it as exists upon the exhaust end of the +rotor. These dummy pistons are shown at the near +end of the rotor in Fig. <a href="#FIG_35">35</a>. They are grooved so as +to form a labyrinth packing, the face of the casing +against which they run being grooved and brass strips +inserted, as shown in Fig. <a href="#FIG_39">39</a>. The dummy pistons +prevent leakage from <i>A</i>, <i>B</i><span class="sup">1</span> and <i>C</i><span class="sup">1</span> to the condenser, +and must, of course, run as closely as practicable to +the rings in the casing, the actual clearance being +from about 0.005 to 0.015 of an inch, again depending +on the size of the machine.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_39" name="FIG_39"></a> + <img src="images/i065.png" + alt="FIG. 39" + title="FIG. 39" + /><br /> +FIG. 39</p> +</div> + +<p>The axial adjustment is controlled by the device +shown at <i>T</i> in Fig. <a href="#FIG_34">34</a> and on a larger scale in Fig. <a href="#FIG_40">40</a>. +The thrust bearing consists of two parts, <i>T</i><span class="sub">1</span> <i>T</i><span class="sub">2</span>. +Each consists of a cast-iron body in which are placed brass +collars. These collars fit into grooves <i>C</i>, turned in +the shaft as shown. The halves of the block are +brought into position by means of screws <i>S</i><span class="sub">1</span> <i>S</i><span class="sub">2</span> acting +on levers <i>L</i><span class="sub">1</span> <i>L</i><span class="sub">2</span> and mounted in the bearing pedestal +and cover. The screws are provided with graduated +heads which permit the respective halves of the thrust +bearing to be set within one one-thousandth of an inch.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_40" name="FIG_40"></a> + <a href="images/i067H.png"> + <img src="images/i067.png" + alt="FIG. 40" + title="FIG. 40" + /> + </a><br /> +FIG. 40</p> +</div> + +<p>The upper screw <i>S</i><span class="sub">2</span> is set so that when the rotor<span class='pagenum'><a name="Page_66" id="Page_66">[66]</a></span> +exerts a light pressure against it through the thrust +block and lever the grooves in the balance pistons are +just unable to come in contact with the dummy strips +in the cylinder. The lower screw <i>S</i><span class="sub">1</span> is then adjusted +to permit about 0.008 to 0.010 of an inch freedom +for the collar between the grooves of the thrust bearing.</p> + +<p>These bearings are carefully adjusted before the +machine leaves the shop, and to prevent either accidental +or unauthorized changes of their adjustment +the adjusting screw heads are locked by the method +shown in Fig. <a href="#FIG_40">40</a>. The screw cannot be revolved +without sliding back the latch <i>L</i><span class="sub">3</span>. To do this the pin +<i>P</i><span class="sub">4</span> must be withdrawn, for which purpose the bearing +cover must be removed.</p> + +<p>In general this adjustment should not be changed +except when there has been some wear of the collars +in the thrust bearing; nevertheless, it is a wise precaution +to go over the adjustment at intervals. The +method of doing this is as follows: The machine should +have been in operation for some time so as to be well +and evenly heated and should be run at a reduced +speed, say 10 per cent. of the normal, during the actual +operation of making the adjustment. Adjust +the upper screw which, if tightened, would push +the spindle away from the thrust bearing toward the +exhaust. Find a position for this so that when the +other screw is tightened the balance pistons can just +be heard to touch, and so the least change of position +inward of the upper screw will cause the contact to +<span class='pagenum'><a name="Page_67" id="Page_67">[67]</a></span>cease. To hear if the balance pistons are touching, +a short piece of hardwood should be placed against +the cylinder casing near the balance piston. If the +<span class='pagenum'><a name="Page_68" id="Page_68">[68]</a></span> +ear is applied to the other end of the piece of +wood the contact of the balance pistons can be very +easily detected. The lower screw should then be +loosened and the upper screw advanced from five +to fifteen one-thousandths, according to the machine, +at which position the latter may be considered to be +set. The lower screw should then be advanced until +the under half of the thrust bearing pushes the rotor +against the other half of the thrust bearing, and from +this position it should be pushed back ten or more +one-thousandths, to give freedom for the rotor between +the thrusts, and locked. A certain amount of +care should be exercised in setting the dummies, to +avoid straining the parts and thus obtain a false +setting.</p> + +<p>The object in view is to have the grooves of the balance +pistons running as close as possible to the collars +in the cylinder, but without danger of their coming +in actual contact, and to allow as little freedom as +possible in the thrust <ins class="correction" title="original: being">bearing</ins> itself, but enough to be +sure that it will not heat. The turbine rotor itself +has scarcely any end thrust, so that all the thrust +bearing has to do is to maintain the above-prescribed +adjustment.</p> + +<p>The blades are so gaged that at all loads the rotor +has a very light but positive thrust toward the running +face of the dummy strips, thus maintaining the proper +clearance at the dummies as determined by the setting +of the proper screw adjustment.</p><p><span class='pagenum'><a name="Page_69" id="Page_69">[69]</a></span></p> + + +<h3>Main Bearings</h3> + +<p>The bearings which support the rotor are shown +at <i>F F</i> in Fig. <a href="#FIG_34">34</a> and in detail in Fig. <a href="#FIG_41">41</a>. The bearing +proper consists of a brass tube <i>B</i> with proper oil +grooves. It has a dowel arm <i>L</i> which fits into a corresponding +recess in the bearing cover and which prevents +the bearing from turning. On this tube are +three concentric tubes, <i>C D E</i>, each fitting over the +other with some clearance so that the shaft is free to +move slightly in any direction. These tubes are held +in place by the nut <i>F</i>, and this nut, in turn, is held by +the small set-screw <i>G</i>. The bearing with the surrounding +tubes is placed inside of the cast-iron shell <i>A</i>, +which rests in the bearing pedestal on the block and +liner <i>H</i>. The packing ring <i>M</i> prevents the leakage +of oil past the bearing. Oil enters the chamber at +one end of the bearing at the top and passes through +the oil grooves, lubricating the journal, and then out +into the reservoir under the bearing. The oil also +fills the clearance between the tubes and forms a +cushion, which dampens any tendency to vibration.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_41" name="FIG_41"></a> + <img src="images/i070.png" + alt="FIG. 41" + title="FIG. 41" + /><br /> +FIG. 41</p> +</div> + +<p>The bearings, being supported by the blocks or +"pads" <i>H</i>, are self-alining. Under these pads are +liners 5, 10, 20, and 50 thousandths in thickness. By +means of these liners the rotor may be set in its proper +running position relative to the stator. This operation +is quite simple. Remove the liners from under +one bearing pad and place them under the opposite +pad until a blade touch is obtained by turning the +rotor over by hand. After a touch has been obtained +<span class='pagenum'><a name="Page_70" id="Page_70">[70]</a></span>on the top, bottom, and both sides, the total radial +blade clearance will be known to equal the thickness +of the liners transferred. The position of the rotor +<span class='pagenum'><a name="Page_71" id="Page_71">[71]</a></span>is then so adjusted that the radial blade clearance is +equalized when the turbine is at operating temperature.</p> + +<p>On turbines running at 1800 revolutions per minute +or under, a split babbitted bearing is used, as shown in +Figs. <a href="#FIG_42A">42<i>a</i></a> and <a href="#FIG_42B">42<i>b</i></a>. +These bearings are self-alining and +have the same liner adjustment as the concentric-sleeve +bearings just described. Oil is supplied through +a hole <i>D</i> in the lower liner pad, and is carried to the +oil groove <i>F</i> through the tubes <i>E E</i>. The oil flows +from the middle of this bearing to both ends instead +of from one end to the other, as in the other type.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_42A" name="FIG_42A"></a> + <img src="images/i072.png" + alt="FIG. 42A" + title="FIG. 42A" + /><br /> +FIG. 42A</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_42B" name="FIG_42B"></a> + <img src="images/i073.png" + alt="FIG. 42B" + title="FIG. 42B" + /><br /> +FIG. 42B</p> +</div> + + +<h3>Packing Glands</h3> + +<p>Where the shaft passes through the casing at either +end it issues from a chamber in which there exists a +vacuum. It is necessary to pack the shaft at these +points, therefore, against the atmospheric pressure, +and this is done by means of a water-gland packing +<i>W W</i> (Fig. <a href="#FIG_34">34</a>). Upon the shaft in Fig. <a href="#FIG_35">35</a>, just in +front of the dummy pistons, will be seen a runner of +this packing gland, which runner is shown upon a +larger scale and from a different direction in Fig. <a href="#FIG_43">43</a>. +To get into the casing the air would have to enter +the guard at <i>A</i> (Fig. <a href="#FIG_44">44</a>), pass over the projecting rings +<i>B</i>, the function of which is to throw off any water +which may be creeping along the shaft by centrifugal +force into the surrounding space <i>C</i>, whence it escapes +by the drip pipe <i>D</i>, hence over the five rings of the +labyrinth packing <i>E</i> and thence over the top of the +revolving blade wheel, it being apparent from Fig. <a href="#FIG_43">43</a> +<span class='pagenum'><a name="Page_72" id="Page_72">[72]</a></span>that there is no way for the air to pass by without +going up over the top of the blades; but water is +admitted to the centrally grooved space through the +<span class='pagenum'><a name="Page_73" id="Page_73">[73]</a></span>pipe shown, and is revolved with the wheel at such +velocity that the pressure due to centrifugal force +exceeds that of the atmosphere, so that it is impossible +<span class='pagenum'><a name="Page_74" id="Page_74">[74]</a></span>for the air to force the water aside and leak in over +the tips of the blades, while the action of the runner +in throwing the water out would relieve the pressure +at the shafts and avoid the tendency of the water +<span class='pagenum'><a name="Page_75" id="Page_75">[75]</a></span> +to leak outward through the labyrinth packing either +into the vacuum or the atmosphere.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_43" name="FIG_43"></a> + <img src="images/i074.png" + alt="FIG. 43" + title="FIG. 43" + /><br /> +FIG. 43</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_44" name="FIG_44"></a> +<span class='pagenum'><a name="Page_76" id="Page_76">[76]</a></span> + <img src="images/i075.png" + alt="FIG. 44" + title="FIG. 44" + /><br /> +FIG. 44</p> +</div> + +<p>The water should come to the glands under a head +of about 10 feet, or a pressure of about 5 pounds, +and be connected in such a way that this pressure +may be uninterruptedly maintained. Its temperature +must be lower than the temperature due to the +vacuum within the turbine, or it will evaporate readily +and find its way into the turbine in the form of steam.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_45" name="FIG_45"></a> + <img src="images/i076.png" + alt="FIG. 45" + title="FIG. 45" + /><br /> +FIG. 45</p> +</div> + +<p>In any case a small amount of the steaming water +will pass by the gland collars into the turbine, so that +if the condensed steam is to be returned to the boilers +the water used in the glands must be of such character +that it may be safely used for feed water. But +whether the water so used is to be returned to the +<span class='pagenum'><a name="Page_77" id="Page_77">[77]</a></span>boilers or not it should never contain an excessive +amount of lime or solid matter, as a certain amount +of evaporation is continually going on in the glands +which will result in the deposit of scale and require +frequent taking apart for cleaning.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_46" name="FIG_46"></a> + <img src="images/i077.png" + alt="FIG. 46" + title="FIG. 46" + /><br /> +FIG. 46</p> +</div> + +<p>When there is an ample supply of good, clean +water the glands may be packed as in Fig. <a href="#FIG_45">45</a>, the +standpipe supplying the necessary head and the supply +valve being opened sufficiently to maintain a small +stream at the overflow. When water is expensive +and the overflow must be avoided, a small float +may be used as in Fig. <a href="#FIG_46">46</a>, the ordinary tank used +by plumbers for closets, etc., serving the purpose +admirably.</p> + +<p>When the same water that is supplied to the glands +is used for the oil-cooling coils, which will be +<span class='pagenum'><a name="Page_78" id="Page_78">[78]</a></span>described in detail later, the coils may be attached to +either of the above arrangements as shown in Fig. <a href="#FIG_47">47</a>.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_47" name="FIG_47"></a> + <img src="images/i078.png" + alt="FIG. 47" + title="FIG. 47" + /><br /> +FIG. 47</p> +</div> + +<p>When the only available supply of pure water is +that for the boiler feed, and the condensed steam is +pumped directly back to the boiler, as shown in Fig. +<a href="#FIG_48">48</a>, the delivery from the condensed-water pumps +may be carried to an elevation 10 feet above the axis +of the glands, where a tank should be provided of +sufficient capacity that the water may have time to +cool considerably before being used. In most of +these cases, if so desired, the oil-cooling water may +come from the circulating pumps of the condenser, +provided there is sufficient pressure to produce circulation, +as is also shown in Fig. <a href="#FIG_48">48</a>.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_48" name="FIG_48"></a> + <img src="images/i079.png" + alt="FIG. 48" + title="FIG. 48" + /><br /> +FIG. 48</p> +</div> + +<p>When the turbine is required to exhaust against a +back pressure of one or two pounds a slightly different +arrangement of piping must be made. The water +in this case must be allowed to circulate through the +<span class='pagenum'><a name="Page_79" id="Page_79">[79]</a></span>glands in order to keep the temperature below 212 +degrees Fahrenheit. If this is not done the water +in the glands will absorb heat from the main castings +of the machine and will evaporate. This evaporation +will make the glands appear as though they were +leaking badly. In reality it is nothing more than +the water in the glands boiling, but it is nevertheless +equally objectionable. This may be overcome by +the arrangement shown in Fig. <a href="#FIG_49">49</a>, where two connections +and valves are furnished at <i>M</i> and <i>N</i>, which +drain away to any suitable tank or sewer. These +valves are open just enough to keep sufficient circulation +so that there is no evaporation going on, which +is evidenced by steam coming out as though the +<span class='pagenum'><a name="Page_80" id="Page_80">[80]</a></span>glands were leaking. These circulating valves may +be used with any of the arrangements above described.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_49" name="FIG_49"></a> + <img src="images/i080.png" + alt="FIG. 49" + title="FIG. 49" + /><br /> +FIG. 49</p> +</div> + + +<h3>The Governor</h3> + +<p>On the right-hand end of the main shaft in Fig. <a href="#FIG_34">34</a> +there will be seen a worm gear driving the governor. +This is shown on a larger scale at <i>A</i> (Fig. <a href="#FIG_50">50</a>). At +the left of the worm gear is a bevel gear driving the +spindle <i>D</i> of the governor, and at the right an eccentric +which gives a vibratory motion to the lever <i>F</i>. +The crank <i>C</i> upon the end of the shaft operates the +oil pump. The speed of the turbine is controlled by +admitting the steam in puffs of greater or less duration +according to the load. The lever <i>F</i>, having its +fulcrum in the collar surrounding the shaft, operates +with each vibration of the eccentric the pilot valve. +The valve is explained in detail later.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_50" name="FIG_50"></a> + <img src="images/i081.png" + alt="FIG. 50" + title="FIG. 50" + /><br /> +FIG. 50</p> +</div> + +<p><span class='pagenum'><a name="Page_81" id="Page_81">[81]</a></span>This form of governor has been superseded by an +improved type, but so many have been made that it +will be well to describe its construction and adjustment. +<span class='pagenum'><a name="Page_82" id="Page_82">[82]</a></span>The two balls <i>W W</i> (Fig. <a href="#FIG_50">50</a>) are mounted +on the ends of bell cranks <i>N</i>, which rest on knife edges. +The other end of the bell cranks carry rollers upon +which rest a plate <i>P</i>, which serves as a support for +the governor spring <i>S</i>. They are also attached by +links to a yoke and sleeve <i>E</i> which acts as a fulcrum +for the lever <i>F</i>. The governor is regulated by means +of the spring <i>S</i> resting on the plate <i>P</i> and compressed +by a large nut <i>G</i> on the upper end of the governor +spindle, which nut turns on a threaded quill <i>J</i>, held +in place by the nut <i>H</i> on the end of the governor +spindle and is held tight by the lock-nut <i>K</i>. To +change the compression of the spring and thereby the +speed of the turbine the lock-nut must first be loosened +and the hand-nut raised to lower the speed or +lowered to raise the speed as the case may be. This +operation may be accomplished while the machine +is either running or at rest.</p> + +<p>The plate <i>P</i> rests upon ball bearings so that by +simply bringing pressure to bear upon the hand-wheel, +which is a part of the quill <i>J</i>, the spring and lock-nut +may be held at rest and adjusted while the rest of +the turbine remains unaffected. Another lever is +mounted upon the yoke <i>E</i> on the pin shown at <i>I</i>, the +other end of which is fastened to the piston of a dash-pot +so as to dampen the governor against vibration. +Under the yoke <i>E</i> will be noticed a small trigger <i>M</i> +which is used to hold the governor in the full-load +position when the turbine is at rest.</p> + +<p>The throwing out of the weights elevates the sleeve +<i>E</i>, carrying with it the collar <i>C</i>, which is spanned by +<span class='pagenum'><a name="Page_83" id="Page_83">[83]</a></span>the lever <i>F</i> upon the shaft <i>H</i>. The later turbines are +provided with an improved form of governor operating +on the same principle, but embodying several important +features. First, the spindle sleeve is integral +with the governor yoke, and the whole rotates about +a vertical stationary spindle, so that two motions are +encountered—a rotary motion and an up and down +motion, according to the position taken by the governor. +This spiral motion almost entirely eliminates +the effect of friction of rest, and thereby enhances the +sensitiveness of the governor. Second, the governor +weights move outward on a parallel motion opposed +directly by spring thrust, thus relieving the fulcrum +entirely of spring thrust. Third, the lay shaft driving +the governor oil pump and reciprocator is located +underneath the main turbine shaft, so that the rotor +may be readily removed without in the least disturbing +the governor adjustment.</p> + + +<h3>The Valve-Gear</h3> + +<p>The valve-gear is shown in section in Fig. <a href="#FIG_51">51</a>, the +main admission being shown at <i>V</i><span class="sub">1</span> at the right, and +the secondary <i>V</i><span class="sub">2</span> at the left of the steam inlet. The +pilot valve <i>F</i> receives a constant reciprocating motion +from the eccentric upon the layshaft of the turbine +through the lever <i>F</i> (Fig. <a href="#FIG_50">50</a>). These reciprocations +run from 150 to 180 per minute. The space beneath +the piston <i>C</i> is in communication with the large steam +chest, where exists the initial pressure through the +port <i>A</i>; the admission of steam to the piston <i>C</i> being +<span class='pagenum'><a name="Page_84" id="Page_84">[84]</a></span>controlled by a needle valve <i>B</i>. The pilot valve +connects the port <i>E</i>, leading from the space beneath +the piston to an exhaust port <i>I</i>.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_51" name="FIG_51"></a> + <a href="images/i085H.png"> + <img src="images/i085.png" + alt="FIG. 51" + title="FIG. 51" + /> + </a><br /> +FIG. 51</p> +</div> + +<p>When the pilot valve is closed, the pressures can +accumulate beneath the piston <i>C</i> and raise the main +admission valve from its seat. When the pilot valve +opens, the pressure beneath the piston is relieved and +it is seated by the helical spring above. If the fulcrum +<i>E</i> (Fig. <a href="#FIG_50">50</a>) of the lever <i>F</i> were fixed the admission +would be of an equal and fixed duration. But +if the governor raises the fulcrum <i>E</i>, the pilot valve +<i>F</i> (Fig. <a href="#FIG_51">51</a>) will be lowered, changing the relations +of the openings with the working edges of the ports.</p> + +<p>The seating of the main admission valve is cushioned +by the dashpot, the piston of which is shown +in section at <i>G</i> (Fig. <a href="#FIG_51">51</a>). The valve may be opened +by hand by means of the lever <i>K</i>, to see if it is +perfectly free.</p> + +<p>The secondary valve is somewhat different in its +action. Steam is admitted to both sides of its actuating +piston through the needle valves <i>M M</i>, and the +chamber from which this steam is taken is connected +with the under side of the main admission valve, so +that no steam can reach the actuating piston of the +secondary valve until it has passed through the primary +valve. When the pilot valve is closed, the +pressures equalize above and below the piston <i>N</i> and +the valve remains upon its seat. When the load +upon the turbine exceeds its rated capacity, the pilot +valve moves upward so as to connect the space above +the piston with the exhaust <i>L</i>, relieving the pressure +<span class='pagenum'><a name="Page_85" id="Page_85">[85]</a></span>upon the upper side and allowing the greater pressure +below to force the valve open, which admits steam +to the secondary stage of the turbine.</p> + +<p><span class='pagenum'><a name="Page_86" id="Page_86">[86]</a></span>It would do no good to admit more steam to the +first stage, for at the rated capacity that stage is +taking all the steam for which the blade area will +afford a passage. The port connecting the upper +side of the piston <i>N</i> with the exhaust may be permanently +closed by means of the hand valve <i>Q</i>, to +be found on the side of the secondary pilot valve +chest, thus cutting the secondary valve entirely out +of action. No dashpot is necessary on this valve, +the compression of the steam in the chamber <i>W</i> by +the fall of the piston being sufficient to avoid shock.</p> + +<p>The timing of the secondary valve is adjusted by +raising or lowering the pilot valve by means of the +adjustment provided. It should open soon enough +so that there will not be an appreciable drop in speed +before the valve comes into play. The economy of +the machine will be impaired if the valve is allowed +to open too soon.</p> + + +<h3>Safety Stop Governor</h3> + +<p>This device is mounted on the governor end of the turbine +shaft, as shown in Figs. <a href="#FIG_52">52</a> and <a href="#FIG_53">53</a>. +When the speed +reaches a predetermined limit, the plunger <i>A</i>, having +its center of gravity slightly displaced from the center +of rotation of the shaft, is thrown radially outward +and strikes the lever <i>B</i>. It will easily be understood +that when the plunger starts outward, the resistance +of spring <i>C</i> is rapidly overcome, since the centrifugal +force increases as the square of the radius, or in this +case the eccentricity of the center of gravity relative +to the center of rotation. Hence, the lever is struck +<span class='pagenum'><a name="Page_87" id="Page_87">[87]</a></span>a sharp blow. This releases the trip <i>E</i> on the outside +of the governor casing, and so opens the steam valve +<i>F</i>, which releases steam from beneath the actuating +piston of a quick-closing throttle valve, located in the +steam line. Thus, within a period of usually less than +one second, the steam is entirely shut off from the +turbine when the speed has exceeded 7 or 8 per cent +of the normal.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_52" name="FIG_52"></a> + <img src="images/i087.png" + alt="FIG. 52" + title="FIG. 52" + /><br /> +FIG. 52</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_53" name="FIG_53"></a> + <img src="images/i088.png" + alt="FIG. 53" + title="FIG. 53" + /><br /> +FIG. 53</p> +</div> + + +<h3>The Oiling System</h3> + +<p>Mounted on the end of the bedplate is the oil pump, +operated from the main shaft of the turbine as previously +stated. This may be of the plunger type +shown in Fig. <a href="#FIG_54">54</a>, or upon the latest turbine, the +rotary type shown in Fig. <a href="#FIG_55">55</a>. Around the bedplate +are located the oil-cooling coils, the oil strainer, the +oil reservoir and the oil pipings to the bearing.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_54" name="FIG_54"></a> + <img src="images/i089.png" + alt="FIG. 54" + title="FIG. 54" + /><br /> +FIG. 54</p> +</div> + +<p><span class='pagenum'><a name="Page_88" id="Page_88">[88]</a></span>The oil reservoir, cooler, and piping are all outside +the machine and easily accessible for cleaning. Usually +a corrugated-steel floor plate covers all this apparatus, +so that it will not be unsightly and accumulate dirt, +particularly when the turbine is installed, so that all +this apparatus is below the floor level; <i>i.e.</i>, when the +top of the bedplate comes flush with the floor line. +<span class='pagenum'><a name="Page_89" id="Page_89">[89]</a></span>In cases where the turbine is set higher, a casing is +usually built around this material so that it can be easily +removed, and forms a platform alongside the machine.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_55" name="FIG_55"></a> +<span class='pagenum'><a name="Page_90" id="Page_90">[90]</a></span> + <a href="images/i090H.png"> + <img src="images/i090.png" + alt="FIG. 55" + title="FIG. 55" + /> + </a><br /> +FIG. 55</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_56" name="FIG_56"></a> +<span class='pagenum'><a name="Page_91" id="Page_91">[91]</a></span> + <a href="images/i091H.png"> + <img src="images/i091.png" + alt="FIG. 56" + title="FIG. 56" + /> + </a><br /> +<ins class="correction" title="original: FIG 50">FIG. 56</ins></p> +</div> + +<p>The oil cooler, shown in Fig. <a href="#FIG_56">56</a>, is of the counter-current +type, the water entering at <i>A</i> and leaving at +<i>B</i>, oil entering at <i>C</i> (opening not shown) and leaving +at <i>D</i>. The coils are of seamless drawn copper, and attached +to the cover by coupling the nut. The water +manifold <i>F</i> is divided into compartments by transverse +<span class='pagenum'><a name="Page_92" id="Page_92">[92]</a></span> +ribs, each compartment connecting the inlet of +each coil with the outlet of the preceding coil, thus +placing all coils in series. These coils are removable +in one piece with the coverplate without disturbing +the rest of the oil piping.</p> + + +<h3>Blading</h3> + +<div class="center"> +<p class="caption"> + <a id="FIG_57" name="FIG_57"></a> + <img src="images/i092.png" + alt="FIG. 57" + title="FIG. 57" + /><br /> +FIG. 57</p> +</div> + +<p>The blades are drawn from a rod consisting of a +steel core coated with copper so intimately connected +with the other metal that when the bar is drawn to +the section required for the blading, the exterior +coating drawn with the rest of the bar forms a +covering of uniform thickness as shown in Fig. <a href="#FIG_57">57</a>. +The bar after being drawn through the correct +section is cut into suitable lengths punched as at <i>A</i> +(Fig. <a href="#FIG_58">58</a>), near the top of the blade, and has a groove +shown at <i>B</i> (Fig. <a href="#FIG_59">59</a>), near the root, stamped in +its concave face, while the blade is being cut to length +and punched. The blades are then set into grooves +<span class='pagenum'><a name="Page_93" id="Page_93">[93]</a></span>cut into the rotor drum or the concave surface of the +casing, and spacing or packing pieces <i>C</i> (Fig. <a href="#FIG_59">59</a>) +placed between them. These spacing pieces are of +soft iron and of the form which is desired that the +passage between the blades shall take. The groove +made upon the inner face of the blade is sufficiently +near to the root to be covered by this spacing piece. +When the groove has been filled the soft-iron pieces +are calked or spread so as to hold the blades firmly +in place. A wire of comma section, as shown at <i>A</i> +(Fig. <a href="#FIG_59">59</a>), is then strung through the punches near +the outer ends of the blades and upset or turned +over as shown at the right in Fig. <a href="#FIG_58">58</a>. This upsetting +is done by a tool which shears the tail of the +comma at the proper width between the blades. The +<span class='pagenum'><a name="Page_94" id="Page_94">[94]</a></span>bent-down portion on either side of the blade holds +it rigidly in position and the portion retained within +the width of the blade would retain the blade in its +<span class='pagenum'><a name="Page_95" id="Page_95">[95]</a></span>radial position should it become loosened or broken +off at the root. This comma lashing, as it is called, +takes up a small proportion only of the blade length +or projection and makes a job which is surprisingly +stiff and rigid, and yet which yields in case of serious +disturbance rather than to maintain a contact which +would result in its own fusing or the destruction of +some more important member.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_58" name="FIG_58"></a> + <img src="images/i093.png" + alt="FIG. 58" + title="FIG. 58" + /><br /> +FIG. 58</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_59" name="FIG_59"></a> + <a href="images/i094H.png"> + <img src="images/i094.png" + alt="FIG. 59" + title="FIG. 59" + /> + </a><br /> +FIG. 59</p> +</div> + + +<h3>Starting Up the Turbine</h3> + +<p>When starting up the turbine for the first time, or +after any extended period of idleness, special care +must be taken to see that everything is in good condition +and that all parts of the machine are clean and +free from injury. The oil piping should be thoroughly +inspected and cleaned out if there is any accumulation +of dirt. The oil reservoirs must be very carefully +wiped out and minutely examined for the presence +of any grit. (Avoid using cotton waste for this, as +a considerable quantity of lint is almost sure to be +left behind and this will clog up the oil passages in +the bearings and strainer.)</p> + +<p>The pilot valves should be removed from the barrel +and wiped off, and the barrels themselves cleaned out +by pushing a soft cloth through them with a piece of +wood. In no case should any metal be used.</p> + +<p>If the turbine has been in a place where there was +dirt or where there has been much dust blowing around, +the bearings should be removed from the spindle and +taken apart and thoroughly cleaned. With care this +can be done without removing the spindle from the +<span class='pagenum'><a name="Page_96" id="Page_96">[96]</a></span>cylinder, by taking off the bearing covers and very +carefully lifting the weight of the spindle off the bearings, +then sliding back the bearings. It is best to +lift the spindle by means of jacks and a rope sling, as, +if a crane is used, there is great danger of lifting the +spindle too high and thereby straining it or injuring +the blades. After all the parts have been carefully +gone over and cleaned, the oil for the bearing lubrication +should be put into the reservoirs by pouring it +into the governor gear case <i>G</i> (Fig. <a href="#FIG_34">34</a>). Enough oil +should be put in so that when the governor, gear case, +and all the bearing-supply pipes are full, the supply +to the oil pump is well covered.</p> + +<p>Special care should be taken so that no grit gets +into the oil when pouring it into the machine. Considerable +trouble may be saved in this respect by +pouring the oil through cloth.</p> + +<p>A very careful inspection of the steam piping is +necessary before the turbine is run. If possible it +should be blown out by steam from the boilers before +it is finally connected to the turbine. Considerable +annoyance may result by neglecting this precaution, +from particles of scale, red lead, gasket, etc., out of the +steam pipe, closing up the passages of the guide blades.</p> + +<p>When starting up, always begin to revolve the +spindle without vacuum being on the turbine. After +the spindle is turning slowly, bring the vacuum up. +The reason for this is, that when the turbine is standing +still, the glands do not pack and air in considerable +quantity will rush through the glands and down +through the exhaust pipe. This sometimes has the +<span class='pagenum'><a name="Page_97" id="Page_97">[97]</a></span>effect of unequal cooling. In case the turbine is used +in conjunction with its own separate condenser, the +circulating pump may be started up, then the turbine +revolved, and afterward the air pump put in operation; +then, last, put the turbine up to speed. In +cases, however, where the turbine exhausts into the +same condenser with other machinery and the condenser +is therefore already in operation, the valve +between the turbine and the condenser system should +be kept closed until after the turbine is revolved, the +turbine in the meantime exhausting through the +relief valve to atmosphere.</p> + +<p>Care must always be taken to see that the turbine +is properly warmed up before being caused to revolve, +but in cases where high superheat is employed always +revolve the turbine just as soon as it is moderately +hot, and before it has time to become exposed to +superheat.</p> + +<p>In the case of highly superheated steam, it is not +undesirable to provide a connection in the steam line +by means of which the turbine may be started up with +saturated steam and the superheat gradually applied +after the shaft has been permitted to revolve.</p> + +<p>For warming up, it is usual practice to set the governor +on the trigger (see Fig. <a href="#FIG_50">50</a>) and open the throttle +valve to allow the entrance of a small amount of +steam.</p> + +<p>It is always well to let the turbine operate at a reduced +speed for a time, until there is assurance that +the condenser and auxiliaries are in proper working +order, that the oil pump is working properly, and +<span class='pagenum'><a name="Page_98" id="Page_98">[98]</a></span>that there is no sticking in the governor or the valve gear.</p> + +<p>After the turbine is up to speed and on the governor, +it is well to count the speed by counting the strokes +of the pump rod, as it is possible that the adjustment +of the governor may have become changed while the +machine has been idle. It is well at this time, while +there is no load on the turbine, to be sure that the +governor controls the machine with the throttle wide +open. It might be that the main poppet valve has +sustained some injury not evident on inspection, or +was leaking badly. Should there be some such defect, +steps should be taken to regrind the valve to its +seat at the first opportunity.</p> + +<p>On the larger machines an auxiliary oil pump is +always furnished. This should be used before starting +up, so as to establish the oil circulation before +the turbine is revolved. After the turbine has reached +speed, and the main oil pump is found to be working +properly, it should be possible to take this pump out +of service, and start it again only when the turbine +is about to be shut down.</p> + +<p>If possible, the load should be thrown on gradually +to obviate a sudden, heavy demand upon the boiler, +with its sometimes attendant priming and rush of +water into the steam pipe, which is very apt to take +place if the load is thrown on too suddenly. A slug +of water will have the effect of slowing down the +turbine to a considerable extent, causing some annoyance. +There is not likely to be the danger of the damage +that is almost sure to occur in the reciprocating +<span class='pagenum'><a name="Page_99" id="Page_99">[99]</a></span>engine, but at the same time it is well to avoid this +as much as possible. A slug of water is obviously +more dangerous when superheated steam is being employed, +owing to the extreme temperature changes possible.</p> + + +<h3>Running</h3> + +<p>While the turbine is running, it should have a certain +amount of careful attention. This, of course, +does not mean that the engineer must stand over it +every minute of the day, but he must frequently inspect +such parts as the lubricators, the oiling system, +the water supply to the glands and the oil-cooling +coil, the pilot valve, etc. He must see that the oil +is up in the reservoir and showing in the gage glass +provided for that purpose, and that the oil is flowing +freely through the bearings, by opening the pet cocks +in the top of the bearing covers. An ample supply of +oil should always be in the machine to keep the suction +in the tank covered.</p> + +<p>Care must be taken that the pump does not draw +too much air. This can usually be discovered by the +bubbling up of the air in the governor case, when +more oil should be added.</p> + +<p>It is well to note from time to time the temperature +of the bearings, but no alarm need be occasioned +because they feel warm to the touch; in fact, a bearing +is all right as long as the hand can be borne upon it +even momentarily. The oil coming from the bearings +should be preferably about 120 degrees Fahrenheit +and never exceed 160 degrees.</p> + +<p><span class='pagenum'><a name="Page_100" id="Page_100">[100]</a></span>It should generally be seen that the oil-cooling coil +is effective in keeping the oil cool. Sometimes the +cooling water deposits mud on the cooling surface, as +well as the oil depositing a vaseline-like substance, +which interferes with the cooling effect. The bearing +may become unduly heated because of this, when the +coil should be taken out at the first opportunity and +cleaned on the outside and blown out by steam on the +inside, if this latter is possible. If this does not +reduce the temperature, either the oil has been in use +too long without being filtered, or the quality of the +oil is not good.</p> + +<p>Should a bearing give trouble, the first symptom +will be burning oil which will smoke and give off dense +white fumes which can be very readily seen and +smelled. However, trouble with the bearings is one +of the most unlikely things to be encountered, and, +if it occurs, it is due to some radical cause, such as +the bearings being pinched by their caps, or grit and +foreign matter being allowed to get into the oil.</p> + +<p>If a bearing gets hot, be assured that there is some +very radical cause for it which should be immediately +discovered and removed. Never, under any circumstances, +imagine that you can nurse a bearing, that +has heated, into good behavior. Turbine bearings +are either all right or all wrong. There are no halfway measures.</p> + +<p>The oil strainer should also be occasionally taken +apart and thoroughly cleaned, which operation may +be performed, if necessary, while the turbine is in +operation. The screens should be cleaned by being +<span class='pagenum'><a name="Page_101" id="Page_101">[101]</a></span>removed from their case and thoroughly blown out +with steam. In the case of a new machine, this may +have to be done every two or three hours. In course +of time, this need only be repeated perhaps once a +week. The amount of dirt found will be an indication +of the frequency with which this cleaning is necessary.</p> + +<p>The proper water pressure, about five pounds per +square inch, must be maintained at the glands. Any +failure of this will mean that there is some big leak in +the piping, or that the water is not flowing properly.</p> + +<p>The pilot valve must be working freely, causing +but little kick on the governor, and should be lubricated +from time to time with good oil.</p> + +<p>Should it become necessary, while operating, to +shut down the condenser and change over to non-condensing +operation, particular care should be observed +that the change is not made too suddenly to +non-condensing, as all the low-pressure sections of the +turbine must be raised to a much higher temperature. +While this may not cause an accident, it is +well to avoid the stresses which necessarily result +from the sudden change of temperature. The same +reasons, of course, do not hold good in changing from +non-condensing to condensing.</p> + + +<h3>Shutting Down</h3> + +<p>When shutting down the turbine the load may be +taken off before closing the throttle; or, as in the case +of a generator operating on an independent load, the +throttle may be closed first, allowing the load to act +<span class='pagenum'><a name="Page_102" id="Page_102">[102]</a></span>as a brake, bringing the turbine to rest quickly. In +most cases, however, the former method will have +to be used, as the turbine generally will have been +operating in parallel with one or more other generators. +When this is the case, partially close the throttle +just before the load is to be thrown off, and if the turbine +is to run without load for some time, shut off +the steam almost entirely in order to prevent any +chance of the turbine running away. There is no +danger of this unless the main valve has been damaged +by the water when wet steam has been used, or +held open by some foreign substance, when, in either +case, there may be sufficient leakage to run the turbine +above speed, while running light. At the same +time, danger is well guarded against by the automatic +stop valve, but it is always well to avoid a possible +danger. As soon as the throttle is shut, stop +the condenser, or, in the case where one condenser +is used for two or more turbines, close the valve between +the turbine and the condenser. Also open the +drains from the steam strainer, etc. This will considerably +reduce the time the turbine requires to come +to rest. Still more time may be saved by leaving the +field current on the generator.</p> + +<p>Care should be taken, when the vacuum falls and +the turbine slows down, to see that the water is shut +off from the glands for fear it may leak out to such an +extent as to let the water into the bearings and impair +the lubricating qualities of the oil.</p><p><span class='pagenum'><a name="Page_103" id="Page_103">[103]</a></span></p> + + +<h3>Inspection</h3> + +<p>At regular intervals thorough inspection should be +made of all parts of the turbine. As often as it +appears necessary from the temperature of the oil, +depending on the quality of the oil and the use of the +turbine, remove the oil-cooling coil and clean it both +on the inside and outside as previously directed; also +clean out the chamber in which it is kept. Put in a +fresh supply of oil. This need not necessarily be new, +but may be oil that has been in use before but has +been filtered. We recommend that an oil filter be +kept for this purpose. Entirely new oil need only +be put into the turbine when the old oil shows marked +deterioration. With a first-class oil this will probably +be a very infrequent necessity, as some new oil +has to be put in from time to time to make up the +losses from leakage and waste.</p> + +<p>Clean out the oil strainer, blowing steam through +the wire gauze to remove any accumulation of dirt. +Every six months to a year take off the bearing covers, +remove the bearings, and take them apart and clean +out thoroughly. Even the best oil will deposit more +or less solid matter upon hot surfaces in time, which +will tend to prevent the free circulation of the oil +through the bearings and effectively stop the cushioning +effect on the bearings. Take apart the main and +secondary valves and clean thoroughly, seeing that all +parts are in good working order. Clean and inspect +the governor and the valve-gear, wiping out any accumulation +of oil and dirt that may appear. Be sure to +<span class='pagenum'><a name="Page_104" id="Page_104">[104]</a></span>clean out the drains from the glands so that any water +that may pass out of them will run off freely and will +not get into the bearings.</p> + +<p>At the end of the first three months, and after that +about once a year, take off the cylinder cover and +remove the spindle. When the turbine is first started +up, there is very apt to be considerable foreign matter +come over in the steam, such as balls of red lead or +small pieces of gasket too small to be stopped by the +strainer. These get into the guide blades in the cylinder +and quite effectively stop them up. Therefore, +the blades should be gone over very carefully, and +any such additional accumulation removed. Examine +the glands and equilibrium ports for any dirt or +broken parts. Particularly examine the glands for +any deposit of scale. All the scale should be chipped +off the gland parts, as, besides preventing the glands +from properly packing, this accumulation will cause +mechanical contact and perhaps cause vibration of the +machine due to lack of freedom of the parts. The +amount of scale found after the first few inspections +will be an indication of how frequently the cleaning +should be done. As is discussed later, any water +that is unsuitable for boiler feed should not be used +in the glands.</p> + +<p>In reassembling the spindle and cover, very great +care must be taken that no blades are damaged and +that nothing gets into the blades. Nearly all the +damage that has been done to blades has resulted +from carelessness in this respect; in fact, it is impossible +to be too careful. Particular care is also to be +<span class='pagenum'><a name="Page_105" id="Page_105">[105]</a></span>taken in assembling all the parts and in handling +them, as slight injury may cause serious trouble. In +no case should a damaged part be put back until the +injury has been repaired.</p> + +<p>If for any reason damaged blades cannot be repaired +at the time, they can be easily removed and the +turbine run again without them until it is convenient +to put in new ones; in fact, machines have been run +at full load with only three-quarters of the total number +of blades. In such an event remove the corresponding +stationary blades as well as the moving +blades, so as not to disturb the balance of the end +thrust.</p> + + +<h3>Conditions Conducive to Successful Operation</h3> + +<p>In the operation of the turbine and the conditions +of the steam, both live and exhaust play a very +important part. It has been found by expensive +experimenting that moisture in the steam has a very +decided effect on the economy of operation; or considerably +more so than in the case of the reciprocating +engine. In the latter engine, 2 per cent. of moisture +will mean very close to 2 per cent. increase in the +amount of water supplied to the engine for a given +power. On the other hand, in the turbine 2 per cent. +moisture will cause an addition of more nearly 4 per +cent. It is therefore readily seen that the drier the +entering steam, the better will be the appearance of +the coal bill.</p> + +<p>By judicious use of first-class separators in connection +with a suitable draining system, such as the +<span class='pagenum'><a name="Page_106" id="Page_106">[106]</a></span>Holly system which returns the moisture separated +from the steam, back to the boilers, a high degree +of quality may be obtained at the turbine with practically +no extra expense during operation. Frequent +attention should be given the separators and traps +to insure their proper operation. The quality of the +steam may be determined from time to time by the +use of a throttling calorimeter. Dry steam, to a great +extent, depends upon the good and judicious design +of steam piping.</p> + +<p>Superheated steam is of great value where it can be +produced economically, as even a slight degree insures +the benefits to be derived from the use of dry +steam. The higher superheats have been found to +increase the economy to a considerable extent.</p> + +<p>When superheat of a high degree (100 degrees +Fahrenheit or above) is used special care must be +exercised to prevent a sudden rise of the superheat +of any amount. The greatest source of trouble in +this respect is when a sudden demand is made for a +large increase in the amount of steam used by the engine, +as when the turbine is started up and the superheater +has been in operation for some time before, +the full load is suddenly thrown on. It will be readily +seen that with the turbine running light and the +superheater operating, there is a very small amount +of steam passing through; in fact, practically none, +and this may become very highly heated in the superheater, +but loses nearly all its superheat in passing +slowly to the turbine; then, when a sudden demand +is made, this very high temperature steam is drawn +<span class='pagenum'><a name="Page_107" id="Page_107">[107]</a></span>into the turbine. This may usually be guarded against +where a separately fired superheater is used, by keeping +the fire low until the load comes on, or, in the case +where the superheater is part of the boiler, by either +not starting up the superheater until after load comes +on, or else keeping the superheat down by mixing +saturated steam with that which has been superheated. +After the plant has been started up there is little +danger from this source, but such precautions should +be taken as seem best in the particular cases.</p> + +<p>Taking up the exhaust end of the turbine, we have +a much more striking departure from the conditions +familiar in the reciprocating engine. Due to the +limits imposed upon the volume of the cylinder of +the engine, any increase in the vacuum over 23 or +24 inches, in the case, for instance, of a compound-condensing +engine, has very little, if any, effect on +the economy of the engine. With the turbine, on the +other hand, any increase of vacuum, even up to the +highest limits, increases the economy to a very considerable +extent and, moreover, the higher the vacuum +the greater will be the increase in the economy for a +given addition to the vacuum. Thus, raising the +vacuum from 27 to 28 inches has a greater effect +than from 23 to 24 inches. For this reason the +engineer will readily perceive the great desirability of +maintaining the vacuum at the highest possible point +consistent with the satisfactory and economical operation +of the condenser.</p> + +<p>The exhaust pipe should always be carried downward +to the condenser when possible, to keep the +<span class='pagenum'><a name="Page_108" id="Page_108">[108]</a></span>water from backing up from the condenser into the +turbine. If the condenser must be located above +the turbine, then the pipe should be carried first downward +and then upward in the U form, in the manner +of the familiar "entrainer," which will be found effectively +to prevent water getting back when the turbine +is operating.</p> + + +<h3>Condensers</h3> + +<p>As has been previously pointed out, the successful +and satisfactory operation of the turbine depends +very largely on the condenser. With the reciprocating +engine, if the condenser will give 25 inches +vacuum, it is considered fairly good, and it is allowed +to run along by itself until the vacuum drops to somewhere +below 20 inches, when it is completely gone +over, and in many cases practically rebuilt and the +vacuum brought back to the original 25 inches. It +has been seen that this sort of practice will never do +in the case of the turbine condenser and, unless the +vacuum can be regularly maintained at 27 or 28 inches, +the condenser is not doing as well as it ought to do, +or it is not of the proper type, unless perhaps the +temperature and the quantity of cooling water available +render a higher vacuum unattainable.</p> + +<p>On account of the great purity of the condensed +steam from the turbine and its peculiar availability +for boiler feed (there being no oil of any kind mixed +with it to injure the boilers), the surface condenser +is very desirable in connection with the turbine. It +further recommends itself by reason of the high +vacuum obtainable.</p> + +<p><span class='pagenum'><a name="Page_109" id="Page_109">[109]</a></span>Where a condenser system capable of the highest +vacuum is installed, the need of utilizing it to its +utmost capacity can hardly be emphasized too strongly. +A high vacuum will, of course, mean special care and +attention, and continual vigilance for air leaks in the +exhaust piping, which will, however, be fully paid +for by the great increase in economy.</p> + +<p>It must not be inferred that a high vacuum is essential +to successful operation of this type of turbine, +for excellent performance both in the matter of steam +consumption and operation is obtained with inferior +vacuum. The choice of a condenser, however, is a +matter of special engineering, and is hardly within the +province of this article.</p> + + +<h3>Oils</h3> + +<p>There are several oils on the market that are suitable +for the purpose of the turbine oiling system, but +great care must be exercised in their selection. In the +first place, the oil must be pure mineral, unadulterated +with either animal or vegetable oils, and must +have been washed free from acid. Certain brands +of oil require the use of sulphuric acid in their manufacture +and are very apt to contain varying degrees +of free acid in the finished product. A sample from +one lot may have almost no acid, while that from +another lot may contain a dangerous amount.</p> + +<p>Mineral oils that have been adulterated, when +heated up, will partially decompose, forming acid. +These oils may be very good lubricants when first +put into use, but after awhile they lose all their good +<span class='pagenum'><a name="Page_110" id="Page_110">[110]</a></span>qualities and become very harmful to the machine +by eating the journals in which they are used. These +oils must be very carefully avoided in the turbine, as +the cheapness of their first cost will in no way pay +for the damage they may do. A very good and simple +way to test for such adulterations is to take up a +quantity of the oil in a test tube with a solution of +borax and water. If there is any animal or vegetable +adulterant present it will appear as a white milk-like +emulsion which will separate out when allowed to +stand. The pure mineral oil will appear at the top +as a clear liquid and the excess of the borax solution +at the bottom, the emulsion being in between. A +number of oils also contains a considerable amount +of paraffin which is deposited in the oil-cooling coil, +preventing the oil from being cooled properly, and in +the pipes and bearings, choking the oil passages and +preventing the proper circulation of the oil and cushioning +effect in the bearing tubes. This is not entirely +a prohibitive drawback, the chief objection being +that it necessitates quite frequently cleaning the +cooling coil, and the oil piping and bearings.</p> + +<p>Some high-class mineral oils of high viscosity are +inclined to emulsify with water, which emulsion appears +as a jelly-like substance. It might be added +that high-grade oils having a high viscosity might +not be the most suitable for turbine use.</p> + +<p>Since the consumption of oil in a turbine is so very +small, being practically due only to leakage or spilling, +the price paid for it should therefore be of secondary +importance, the prime consideration being its suitability +for the purpose.</p> + +<p><span class='pagenum'><a name="Page_111" id="Page_111">[111]</a></span>In some cases a central gravity system will be employed, +instead of the oil system furnished with the +turbine, which, of course, will be a special consideration.</p> + +<p>For large installations a central gravity oiling system +has much to recommend it, but as it performs +such an important function in the power plant, and +its failure would be the cause of so much damage, +every detail in connection with it should be most +carefully thought out, and designed with a view that +under no combination of circumstances would it be +possible for the system to become inoperative. One +of the great advantages of such a system is that it +can be designed to contain very large quantities of +oil in the settling tanks; thus the oil will have quite +a long rest between the times of its being used in the +turbine, which seems to be very helpful in extending +the life of the oil. Where the oil can have a long rest +for settling, an inferior grade of oil may be used, +providing, however, that it is absolutely free of acid.</p> + + + +<hr class="major" /><p><span class='pagenum'><a name="Page_112" id="Page_112">[112]</a></span></p> +<h2><a name="V_PROPER_METHOD_OF_TESTING_A_STEAM_TURBINE3" id="V_PROPER_METHOD_OF_TESTING_A_STEAM_TURBINE3"></a>V. PROPER METHOD OF TESTING A STEAM TURBINE<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a></h2> + +<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> Contributed to <i>Power</i> by Thomas Franklin.</p></div> + + +<p><span class="smcap">The</span> condensing arrangements of a turbine are +perhaps mainly instrumental in determining the +method of test. The condensed steam alone, issuing +from a turbine having, for example, a barometric or +jet condenser, cannot be directly measured or weighed, +unless by meter, and these at present are not sufficiently +accurate to warrant their use for test purposes, +if anything more than approximate results are desired. +The steam consumed can, in such a case, only +be arrived at by measuring the amount of condensing +water (which ultimately mingles with the condensed +steam), and subtracting this quantity from the condenser's +total outflow. Consequently, in the case of +turbines equipped with barometric or jet condensers, +it is often thought sufficient to rely upon the measurement +taken of the boiler feed, and the boiler's initial +and final contents. Turbines equipped with surface-condensing +plants offer better facilities for accurate +steam-consumption calculations than those plants in +which the condensed exhaust steam and the circulating +water come into actual contact, it being necessary +<span class='pagenum'><a name="Page_113" id="Page_113">[113]</a></span>with this type simply to pump the condensed steam +into a weighing or measuring tank.</p> + +<p>In the case of a single-flow turbine of the Parsons +type, the covers should be taken off and every row of +blades carefully examined for deposits, mechanical +irregularities, deflection from the true radial and vertical +positions, etc. The blade clearances also should +be gaged all around the circumference, to insure this +clearance being an average working minimum. On no +account should a test be proceeded with when any +doubt exists as to the clearance dimensions.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_60" name="FIG_60"></a> + <img src="images/i113.png" + alt="FIG. 60" + title="FIG. 60" + /><br /> +FIG. 60</p> +</div> + +<p>The dummy rings of a turbine, namely, those rings +which prevent excessive leakage past the balancing +pistons at the high-pressure end, should have especial +attention before a test. A diagrammatic sketch of +a turbine cylinder and spindle is shown in Fig. <a href="#FIG_60">60</a>, for +the benefit of those unfamiliar with the subject. In +this <i>A</i> is the cylinder or casing, <i>B</i> the spindle or rotor, +and <i>C</i> the blades. The balancing pistons, <i>D</i>, <i>E</i>, and +<i>F</i>, the pressure upon which counterbalances the axial +thrust upon the three-bladed stages, are grooved, the +brass dummy rings <i>G G</i> in the cylinder being alined +within a few thousandths of an inch of the grooved +<span class='pagenum'><a name="Page_114" id="Page_114">[114]</a></span>walls, as indicated. After these rings have been +turned (the turning being done after the rings have +been calked in the cylinder), it is necessary to insure +that each ring is perfectly bedded to its respective +grooved wall so that when running the several small +clearances between the groove walls and rings are +equal. A capital method of thus bedding the dummy +rings is to grind them down with a flour of emery or +carborundum, while the turbine spindle is slowly +revolving under steam. Under these conditions the +operation is performed under a high temperature, and +any slight permanent warp the rings may take is thus +accounted for. The turbine thrust-block, which maintains +the spindle in correct position relatively to the +spindle, may also be ground with advantage in a similar manner.</p> + +<p>The dummy rings are shown on a large scale in +Fig. <a href="#FIG_61">61</a>, and their preliminary inspection may be made +in the following manner:</p> + +<p>The spindle has been set and the dummy rings <i>C</i> +are consequently within a few thousandths of an inch +of the walls <i>d</i> of the spindle dummy grooves <i>D</i>. The +clearances allowed can be gaged by a feeler placed +between a ring and the groove wall. Before a test the +spindle should be turned slowly around, the feelers +being kept in position. By this means any mechanical +flaws or irregularities in the groove walls may be +detected.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_61" name="FIG_61"></a> + <img src="images/i115.png" + alt="FIG. 61" + title="FIG. 61" + /><br /> +FIG. 61</p> +</div> + +<p>It has sometimes been found that the groove walls, +under the combined action of superheated steam and +friction, in cases where actual running contact has +<span class='pagenum'><a name="Page_115" id="Page_115">[115]</a></span>occurred, have worn very considerably, the wear taking +the form of a rapid crumbling away. It is possible, +however, that such deterioration may be due solely to +the quality of the steel from which the spindle is forged. +Good low-percentage carbon-annealed steel ought to +withstand considerable friction; at all events the wear +under any conditions should be uniform. If the surfaces +of both rings and grooves be found in bad condition, +they should be re-ground, if not sufficiently +worn to warrant skimming up with a tool.</p> + +<p>As the question of dummy leakage is of very considerable +importance during a test, it may not be inadvisable +to describe the manner of setting the spindle +and cylinder relatively to one another to insure minimum +leakage, and the methods of noting their conduct +<span class='pagenum'><a name="Page_116" id="Page_116">[116]</a></span>during a prolonged run. In Fig. <a href="#FIG_62">62</a>, showing the +spindle, <i>B</i> is the thrust (made in halves), the rings <i>O</i> +of which fit into the grooved thrust-rings <i>C</i> in the +spindle. Two lugs <i>D</i> are cast on each half of the +thrust-block. The inside faces of these lugs are machined, +and in them fit the ball ends of the levers <i>E</i>, +the latter being fulcrumed at <i>F</i> in the thrust-bearing +cover. The screws <i>G</i>, working in bushes, also fit into +the thrust-bearing cover, and are capable of pushing +against the ends of the levers <i>E</i> and thus adjusting the +separate halves of the block in opposite directions.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_62" name="FIG_62"></a> + <img src="images/i116.png" + alt="FIG. 62" + title="FIG. 62" + /><br /> +FIG. 62</p> +</div> + +<p>The top half of the turbine cylinder having been +lifted off, the spindle is set relatively to the bottom +half by means of the lower thrust-block screw <i>G</i>. This +screw is then locked in position and the top half of +<span class='pagenum'><a name="Page_117" id="Page_117">[117]</a></span>the cover then lowered into place. With this method +great care must necessarily be exercised when lowering +the top cover; otherwise the brass dummy rings may +be damaged.</p> + +<p>A safer method is to set the dummy rings in the +center of the grooves of the spindle, and then to lower +the cover, with less possibility of contact. There +being usually plenty of side clearance between the +blades of a turbine, it may be deemed quite safe to +lock the thrust-block in its position, by screwing the +screws <i>G</i> up lightly, and then to turn on steam and +begin running slowly.</p> + +<p>Next, the spindle may be very carefully and gradually +worked in the required direction, namely, in that direction +which will tend to bring the dummy rings and +groove walls into contact, until actual but very light +contact takes place. The slightest noise made by the +rubbing parts inside the turbine can be detected by +placing one end of a metal rod onto the casing in +vicinity of the dummy pistons, and letting the other +end press hard against the ear. Contact between the +dummy rings and spindle being thus demonstrated, +the spindle must be moved back by the screws, but +only by the slightest amount possible. The merest +fraction of a turn is enough to break the contact, +which is all that is required. In performing this +operation it is important, during the axial movements +of the spindle, to adjust the halves of the thrust-block +so that there can exist no possible play which would +leave the spindle free to move axially and probably +vibrate badly.</p> + +<p><span class='pagenum'><a name="Page_118" id="Page_118">[118]</a></span>After ascertaining the condition of the dummy rings, +attention might next be turned to the thrust-block, +which must not on any account be tightened up too +much. It is sufficient to say that the actual requirements +are such as will enable a very thin film of oil +to circulate between each wall of the spindle thrust-grooves +and the brass thrust-blocks ring. In other +words, there should be no actual pressure, irrespective +of that exerted by the spindle when running, upon +the thrust-block rings, due to the separate halves +having been nipped too tightly. The results upon a +test of considerable friction between the spindle and +thrust-rings are obvious.</p> + +<p>The considerations outlined regarding balancing +pistons and dummy rings can be dispensed with in connection +with impulse turbines of the De Laval and +Rateau types, and also with double-flow turbines of a +type which does not possess any dummies. The same +general considerations respecting blade conditions and +thrust-blocks are applicable, especially to the latter +type. With pure so-called impulse turbines, where +the blade clearances are comparatively large, the preliminary +blade inspection should be devoted to the +mechanical condition of the blade edges and passages. +As the steam velocities of these types are usually +higher, the importance of minimizing the skin friction +and eliminating the possibility of eddies is great.</p> + +<p>Although steam leakage through the valves of a +turbine may not materially affect its steam consumption, +unless it be the leakage through the overload +valve during a run on normal full load, a thorough +<span class='pagenum'><a name="Page_119" id="Page_119">[119]</a></span>examination of all valves is advocated for many reasons. +In a turbine the main steam-inlet valve is usually +operated automatically from the governor; and whether +it be of the pulsating type, admitting the steam in +blasts, or of the non-pulsating throttling type, it is +equally essential to obtain the least possible friction +between all moving and stationary parts. Similar remarks +apply to the main governor, and any sensitive +transmitting mechanism connecting it with any of the +turbine valves. If a safety or "runaway" governor +is possessed by the machine to be tested, this should +invariably be tried under the requisite conditions before +proceeding farther. The object of this governor +being automatically to shut off all steam from the +turbine, should the latter through any cause rise above +the normal speed, it is often set to operate at about +12 to 15 per cent. above the normal. Thus, a turbine +revolving at about 3000 revolutions per minute would +be closed down at, say, 3500, which would be within +the limit of "safe" speed.</p> + + +<h3>Importance of Oiling System and Water Service</h3> + +<p>The oil question, being important, should be solved +in the early stages previously, if possible, to any official +or unofficial consumption tests. Whether the oil be +supplied to the turbine bearings by a self-contained +system having the oil stored in the turbine bedplate +or by gravity from a separate oil source, does not +affect the question in its present aspect. The necessary +points to investigate are four in number, and may be +headed as follows:</p> + +<ol class="parna"> +<li>(<i>a</i>) Examination of pipes and partitions for oil +leakage.</li> + +<li>(<i>b</i>) Determination of volume of oil flowing through +each bearing per unit of time.</li> + +<li>(<i>c</i>) Examination for signs of water in oil.</li> + +<li>(<i>d</i>) Determination of temperature rise between inlet +and outlet of oil bearings.</li> +</ol> + + + +<p><span class='pagenum'><a name="Page_120" id="Page_120">[120]</a></span> +The turbine supplied with oil by the gravity or any +other separate system holds an advantage over the +ordinary self-contained machine, inasmuch as the oil +pipes conveying oil into and from the bearings can +be easily approached and, if necessary, repaired. On +the other hand, the machine possessing its own oil +tank, cooling chamber and pump is somewhat at a +disadvantage in this respect, as a part of the system +is necessarily hidden from view, and, further, it is not +easily accessible. The leakage taking place in any +system, if there be any, must, however, be detected and stopped.</p> + +<p>Fig. <a href="#FIG_63">63</a> is given to illustrate a danger peculiar to +the self-contained oil system, in which the oil and +oil-cooling chambers are situated adjacently in the +turbine bedplate. One end of the bedplate only is +shown; <i>B</i> is a cast-iron partition dividing the oil chamber +<i>C</i> from the oil-cooling chamber <i>D</i>. Castings of +this kind have sometimes a tendency to sponginess +and the trouble consequent upon this weakness would +take the form of leakage between the two chambers. +Of course this is only a special case, and the conditions +named are hardly likely to exist in every similarly +designed plant. The capacity of oil, and especially +<span class='pagenum'><a name="Page_121" id="Page_121">[121]</a></span>of hot oil, to percolate through the most minute pores +is well known. Consequently, in advocating extreme +caution when dealing with oil leakage, no apology is +needed.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_63" name="FIG_63"></a> + <img src="images/i121.png" + alt="FIG. 63" + title="FIG. 63" + /><br /> +FIG. 63</p> +</div> + +<p>It may be stated without fear of contradiction that +the oil in a self-contained system, namely, a system +in which the oil, stored in a reservoir near or underneath +the turbine, passes only through that one turbine's +bearings, and immediately back to the storage +compartment, deteriorates more rapidly than when +circulating around an "entire" system, such as the +gravity or other analogous system. In the latter, the +oil tanks are usually placed a considerable distance +from the turbine or turbines, with the oil-cooling +arrangements in fairly close proximity. The total +length of the oil circuit is thus considerably increased, +incidentally increasing the relative cooling capacity of +the whole plant, and thereby reducing the loss of oil +by vaporization.</p> + +<p><span class='pagenum'><a name="Page_122" id="Page_122">[122]</a></span>The amount of oil passing through the bearings can +be ascertained accurately by measurement. With a +system such as the gravity it is only necessary to run +the turbine up to speed, turn on the oil, and then, over +a period, calculate the volume of oil used by measuring +the fall of level in the storage tank and multiplying +by its known cross-sectional area. In those cases +where the return oil, after passing through the bearings, +is delivered back into the same tank from which +it is extracted, it is of course necessary, during the +period of test, to divert this return into a separate +temporary receptacle. Where the system possesses +two tanks, one delivery and one return (a superior +arrangement), this additional work is unnecessary. +The same method can be applied to individual turbines +pumping their own oil from a tank in the bedplate; +the return oil, as previously described, being temporarily +prevented from running back to the supply.</p> + +<p>The causes of excessive oil consumption by bearings +are many. There is an economical mean velocity at +which the oil must flow along the revolving spindle; +also an economical mean pressure, the latter diminishing +from the center of the bearing toward the ends. +The aim of the economist must therefore be in the +direction of adjusting these quantities correctly in +relation to a minimum supply of oil per bearing; and +the principal factors capable of variation to attain +certain requirements are the several bearing clearances +measured as annular orifices, and the bearing diameters.</p> + +<p>It is not always an easy matter to detect the presence +of water in an oil system, and this difficulty is increased +<span class='pagenum'><a name="Page_123" id="Page_123">[123]</a></span>in large circuits, as the water, when the oil is not flowing, +generally filters to the lowest members and pipes +of the system, where it cannot usually be seen. A considerable +quantity of water in any system, however, +indicates its presence by small globular deposits on +bearings and spindles, and in the worst cases the water +can clearly be seen in a small sample tapped from the +oil mains. There is only one effective method of +ridding the oil of this water, and this is by allowing the +whole mass of oil in the system to remain quiescent +for a few days, after which the water, which falls to +the lowest parts, can be drained off. A simple method +of clearing out the system is to pump all the oil the +whole circuit contains through the filters, and thence +to a tank from which all water can be taken off. +One of the ordinary supply tanks used in the gravity +system will serve this purpose, should a temporary +tank not be at hand. If necessary, the headers and +auxiliary pipes of the system can be cleaned out before +circulating the oil again, but as this is rather a large +undertaking, it need only be resorted to in serious cases.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_64" name="FIG_64"></a> + <img src="images/i124.png" + alt="FIG. 64" + title="FIG. 64" + /><br /> +FIG. 64</p> +</div> + +<p>It is seldom possible to discover the correct and +permanent temperature rise of the circulating oil in a +turbine within the limited time usually alloted for a +test. After a continuous run of one hundred hours +it is possible that the temperature at the bearing outlets +may be lower than it was after the machine had +run for, say, only twenty hours. As a matter of fact +an oil-temperature curve plotted from periodical readings +taken over a continuous run of considerable +<span class='pagenum'><a name="Page_124" id="Page_124">[124]</a></span>length usually reaches a maximum early, afterward +falling to a temperature about which the fluctuations +are only slight during the remainder of the run. Fig. <a href="#FIG_64">64</a> +illustrates an oil-temperature curve plotted from +readings taken over a period of twenty-four hours. +In this case the oil system was of the gravity description, +the capacity of the turbine being about 6000 +kilowatts. The bearings were of the ordinary white-metal +spherical type. Over extended runs of hundreds +and even thousands of hours, the above deductions +may be scarcely applicable. Running without break +for so long, a small turbine circulating its own lubricant +would possibly require a renewal of the oil before the +run was completed, in the main owing to excessive +temperature rise and consequent deterioration of the +quality of the oil. Under these conditions the probabilities +are that several temperature fluctuations might +occur before the final maximum, and more or less +constant, temperature was reached. In this connection, +<span class='pagenum'><a name="Page_125" id="Page_125">[125]</a></span>however, the results obtained are to a very large +extent determined by the general mechanical design +and construction of the oiling system and turbine. A +reference to Fig. <a href="#FIG_63">63</a> again reveals at once a weakness +in that design, namely, the unnecessarily close proximity +in which the oil and water tanks are placed.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_65" name="FIG_65"></a> + <img src="images/i125.png" + alt="FIG. 65" + title="FIG. 65" + /><br /> +FIG. 65</p> +</div> + +<p>A design of thermometer cup suitable for oil thermometers +is given in Fig. <a href="#FIG_65">65</a> in which <i>A</i> is an end view +of the turbine bedplate, <i>B</i> is a turbine bearing and <i>C</i> +and <i>D</i> are the inlet and outlet pipes, respectively. +<span class='pagenum'><a name="Page_126" id="Page_126">[126]</a></span>The thermometer fittings, which are placed as near the +bearing as is practicable, are made in the form of an +angular tee fitting, the oil pipes being screwed into +its ends. The construction of the oil cup and tee +piece is shown in the detail at the left where <i>A</i> is the +steel tee piece, into which is screwed the brass thermometer +cup <i>B</i>. The hollow bottom portion of this +cup is less than 1/16 of an inch in thickness. The top +portion of the bored hole is enlarged as shown, and into +this, around the thermometer, is placed a non-conducting +material. The cup itself is generally filled +with a thin oil of good conductance.</p> + +<p>Allied to the oil system of a turbine plant is the water +service, of comparatively little importance in connection +with single self-contained units of small capacity, +where the entire service simply consists of a few coils +and pipes, but of the first consideration in large installations +having numerous separate units supplied +by oil and water from an exterior source. The largest +turbine units are often supplied with water for cooling +the bearings and other parts liable to attain high temperature. +Although the water used for cooling the +bearings indirectly supplements the action taking +place in the separate oil coolers, it is of necessity a +separate auxiliary service in itself, and the complexity +of the system is thus added to. A carefully constructed +water service, however, is hardly likely to give trouble +of a mechanical nature. The more serious deficiencies +usually arise from conditions inherent to the design, +and as such must be approached.</p><p><span class='pagenum'><a name="Page_127" id="Page_127">[127]</a></span></p> + + +<h3>Special Turbine Features to be Inquired into</h3> + +<p>Before leaving the prime mover itself, and proceeding +to the auxiliary plant inspection, it may be well to +instance a few special features relating to the general +conduct of a turbine, which it is the duty of a tester +to inquire into. There are certain specified qualifications +which a machine must hold when running under +its commercial conditions, among these being lack of +vibration of both turbine and machinery driven, be it +generator or fan, the satisfactory running of auxiliary +turbine parts directly driven from the turbine spindle, +minimum friction between the driving mediums, such +as worm-wheels, pumps, fans, etc., slight irregularities +of construction, often resulting in heated parts and +excessive friction and wear, and must therefore be +detected and righted before the final test. Furthermore, +those features of design—and they are not infrequent +in many machines of recent development—which, +in practice, do not fulfil theoretical expectations, +must be re-designed upon lines of practical consistency. +The experienced tester's opinion is often at this point +invaluable. To illustrate the foregoing, +Figs. <a href="#FIG_66">66</a>, <a href="#FIG_67">67</a>, and <a href="#FIG_68">68</a> +are given, representing, respectively, three +distinct phases in the evolution of a turbine part, +namely, the coupling. Briefly, an ordinary coupling +connecting a driving and a driven shaft becomes +obstinate when the two separate spindles which it +connects are not truly alined. The desire of turbine +manufacturers has consequently been to design a +flexible coupling, capable of accommodating a certain +<span class='pagenum'><a name="Page_128" id="Page_128">[128]</a></span> +want of alinement between the two spindles without +in any way affecting the smooth running of the whole unit.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_66" name="FIG_66"></a> + <img src="images/i128a.png" + alt="FIG. 66" + title="FIG. 66" + /><br /> +FIG. 66</p> +</div> + +<div class="center"> +<p class="caption"> + <a id="FIG_67" name="FIG_67"></a> + <img src="images/i128b.png" + alt="Fig. 67" + title="Fig. 67" + /><br /> +Fig. <a href="#FIG_67">67</a></p> +</div> + +<p>In Fig. <a href="#FIG_66">66</a> <i>A</i> is the turbine spindle end and <i>B</i> the +generator spindle end, which it is required to drive. +It will be seen from the cross-sectional end view that +both spindle ends are squared, the coupling <i>C</i>, with a +square hole running through it, fitting accurately over +both spindle ends as shown. Obviously the fit between +the coupling and spindle in this case must be +close, otherwise considerable wear would take place; +and equally obvious is the fact than any want of +alinement between the two spindles <i>A</i> and <i>B</i> will be +accompanied by a severe strain upon the coupling, and +incidentally by many other troubles of operation of +which this inability of the coupling to accommodate +<span class='pagenum'><a name="Page_129" id="Page_129">[129]</a></span>itself to a little want of alinement is the inherent cause.</p> + +<p>Looking at the coupling illustrated in Fig. <a href="#FIG_67">67</a>, it +<span class='pagenum'><a name="Page_130" id="Page_130">[130]</a></span>will be seen that something here is much better adapted +to dealing with troubles of alinement. The turbine +and generator spindles <i>A</i> and <i>B</i>, respectively, are +coned at the ends, and upon these tapered portions are +shrunk circular heads <i>C</i> and <i>D</i> having teeth upon their +outer circumferences. Made in halves, and fitting +over the heads, is a sleeve-piece, with teeth cut into +its inner bored face. The teeth of the heads and sleeve +are proportioned correctly to withstand, without +strain, the greatest pressure liable to be thrown upon +them. There is practically no play between the teeth, +but there exists a small annular clearance between +the periphery of the heads and the inside bore of the +sleeve, which allows a slight lack of alinement to exist +between the two spindles, without any strain whatever +being felt by the coupling sleeve <i>E</i>. The nuts +<i>F</i> and <i>G</i> prevent any lateral movement of the coupling +heads <i>C</i> and <i>D</i>. For all practical requirements this +type of coupling is satisfactory, as the clearances +allowed between sliding sleeve and coupling heads +can always be made sufficient to accommodate a considerable +want of alinement, far beyond anything +which is likely to occur in actual practice. Perhaps +the only feature against it is its lack of simplicity of +construction and corresponding costliness.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_68" name="FIG_68"></a> + <img src="images/i129.png" + alt="FIG. 68" + title="FIG. 68" + /><br /> +FIG. 68</p> +</div> + +<p>The type illustrated in Fig. <a href="#FIG_68">68</a> is a distinct advance +upon either of the two previous examples, because, +theoretically at least, it is capable of successfully +accommodating almost any amount of spindle movement. +The turbine and generator spindle ends, <i>A</i> and +<i>B</i>, have toothed heads <i>C</i> and <i>D</i> shrunk upon them, +<span class='pagenum'><a name="Page_131" id="Page_131">[131]</a></span>the heads being secured by the nuts <i>E</i> and <i>F</i>. The +teeth in this case are cut in the enlarged ends as shown. +A sleeve <i>G</i>, made in halves, fits over the heads, and +the teeth cut in each half engage with those of their +respective heads. All the teeth and teeth faces are +cut radially, and a little side play is allowed.</p> + + +<h3>The Condenser</h3> + +<p>To some extent, as previously remarked, the condenser +and condensing arrangements are instrumental +in determining the lines upon which a test ought to be +carried out. In general, the local features of a plant +restrict the tester more or less in the application of his +general methods. A thorough inspection, including +some preliminary tests if necessary, is as essential to +the good conduct of the condensing plant as to the +turbine above it. It may be interesting to outline +the usual course this inspection takes, and to draw +attention to a few of the special features of different +plants. For this purpose a type of vertical condenser +is depicted in Fig. <a href="#FIG_69">69</a>. Its general principle will be +gathered from the following description:</p> + +<p>Exhaust steam from the turbine flows down the pipe +<i>T</i> and enters the condenser at the top as shown, where +it at once comes into contact with the water tubes in +<i>W</i>. These tubes fill an annular area, the central un-tubed +portion below the baffle cap <i>B</i> forming the vapor +chamber. The condensed steam falls upon the bottom +tube-plate <i>P</i> and is carried away by the pipe <i>S</i> leading +to the water pump <i>H</i>. The Y pipe <i>E</i> terminating +above the level of the water in the condenser +<span class='pagenum'><a name="Page_132" id="Page_132">[132]</a></span>enters the dry-air pump section pipe <i>A</i>. Cold circulating +water enters the condenser at the bottom, +through the pipe <i>I</i>, and entering the water chamber <i>X</i> +proceeds upward through the tubes into the top-water +chamber <i>Y</i>, and from there out of the condenser +through the exit pipe. It will be observed that the +vapor extracted through the plate <i>P</i> passes on its journey +out of the condenser through the cooling chamber +<i>D</i> surrounded by the cold circulating water. This, of +course, is a very advantageous feature. At <i>R</i> is the +condenser relief, at <i>U</i> the relief valve for the water chambers.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_69" name="FIG_69"></a> + <img src="images/i132.png" + alt="FIG. 69" + title="FIG. 69" + /><br /> +FIG. 69</p> +</div> + +<p><span class='pagenum'><a name="Page_133" id="Page_133">[133]</a></span>A new condenser, especially if it embody new and +untried features, generally requires a little time and +patience ere the best results can be obtained from it. +Perhaps the quickest and most satisfactory method of +getting at the weak points of this portion of a plant is +to test the various elements individually before applying +a strict load test. Thus, in dealing with a condenser +similar to that illustrated in Fig. <a href="#FIG_69">69</a>, the careful tester +would probably make, in addition to a thorough mechanical +examination, three or four individual vacuum +and water tests. A brief description of these will be +given. The water test, the purpose of which is to +discover any leakage from the tubes, tube-plates, +water pipes, etc., into portions of the steam or air +chambers, should be made first.</p> + + +<h3>Water Tests of Condenser</h3> + +<p>The condenser is first thoroughly dried out, particular +care being given to the outside of the tubes +and the bottom tube-plate <i>P</i>. Water is then circulated +through the tubes and chambers for an hour or +two, after which the pumps are stopped, all water is +allowed to drain out and a careful examination is +made inside. Any water leaking from the tubes above +the bottom baffle-plate will ultimately be deposited +upon that plate. It is essential to stop this leakage +if there be any, otherwise the condensed steam measured +during the consumption test will be increased to +the extent of the leakage. A slight leakage in a large +condenser will obviously not affect the results to any +serious extent. The safest course to adopt when a +<span class='pagenum'><a name="Page_134" id="Page_134">[134]</a></span>leak is discovered and it is found inopportune to effect +immediate repair is to measure the actual volume of +leakage over a specified period, and the quantity then +being known it can be subtracted from the volume of +the condensed steam at the end of the consumption test.</p> + +<p>It is equally essential that no leakage shall occur +between the bottom tube-plate <i>P</i> and the tube ends. +The soundness of the tube joints, and the joint at the +periphery of the tube-plate can be tested by well covering +the plate with water, the water chamber <i>W</i> and +cooling chamber having been previously emptied, and +observing the under side of the plate. It must be +admitted that the practice of measuring the extent of +a water leak over a period, and afterward with this +knowledge adjusting the obtained quantities, is not +always satisfactory. On no account should any test +be made with considerable water leakage inside the +condenser. The above method, however, is perhaps +the most reliable to be followed, if during its conduct +the conditions of temperature in the condenser are +made as near to the normal test temperature as possible. +There are many condensers using salt water in +their tubes, and in these cases it would seem natural +to turn to some analytical method of detecting the +amount of saline and foreign matter leaking into the +condensed steam. Unless, however, only approximate +results are required, such methods are not advocated. +There are many reasons why they cannot be relied +upon for accurate results, among these being the variation +in the percentage of saline matter in the sea-water, +<span class='pagenum'><a name="Page_135" id="Page_135">[135]</a></span>the varying temperature of the condenser tubes +through which the water flows, and the uncertainty +of such analysis, especially where the percentage +leakage of pure saline matter is comparatively small.</p> + + +<h3>The Vacuum Test</h3> + +<p>Having convinced himself of the satisfactory conduct +of the condenser under the foregoing simple +preparatory water tests, the tester may safely pass +to considerations of vacuum. There exists a good +old-fashioned method of discovering the points of +leakage in a vacuum chamber, namely, that of applying +the flame of a candle to all seams and other vulnerable +spots, which in the location of big leaks is +extremely valuable. Assuming that the turbine joints +and glands have been found capable of preventing any +inleak of air, with only a small absolute pressure of +steam or air inside it, and, further, an extremely important +condition, with the turbine casing at high and +low temperatures, separately, a vacuum test can be +conducted on the condenser alone.</p> + +<p>This test consists of three operations. In the first +place a high vacuum is obtained by means of the air +pump, upon the attainment of which communication +with everything else is closed, and results noted. The +second operation consists in repeating the above with +the water circulating through the condenser tubes, the +results in this case also being carefully tabulated. Before +conducting the third test, the condensers must be +thoroughly warmed throughout, by running the turbine +for a short time if necessary, and after closing +<span class='pagenum'><a name="Page_136" id="Page_136">[136]</a></span>communication with everything, allowing the vacuum to +slowly fall.</p> + +<p>A careful consideration and comparison of the foregoing +tests will reveal the capabilities of the condenser +in the aspect in which it is being considered, and will +suggest where necessary the desirable steps to be taken.</p> + + + +<hr class="major" /><p><span class='pagenum'><a name="Page_137" id="Page_137">[137]</a></span></p> +<h2><a name="VI_TESTING_A_STEAM_TURBINE4" id="VI_TESTING_A_STEAM_TURBINE4"></a>VI. TESTING A STEAM TURBINE<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a></h2> + +<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> Contributed to <i>Power</i> by Thomas Franklin.</p></div> + + +<h3>Special Auxiliary Plant for Consumption Test</h3> + +<p><span class="smcap">There</span> are one or two points of importance in the +conduct of a test on a turbine and these will be briefly +touched upon. Fig. <a href="#FIG_70">70</a> illustrates the general arrangement +of the special auxiliary plant necessary for +carrying through a consumption test, when the turbine +exhaust passes through a surface condenser. +The condensed steam, after leaving the condenser, +passes along the pipe <i>A</i> to the pump, and is then forced +along the pipe <i>B</i> (leading under ordinary circumstances +to the hot-well), through the main water +valve <i>C</i> directly to the measuring tanks. To enter +these the water has to pass through the valves <i>D</i> and +<i>E</i>, while the valves <i>F</i> and <i>G</i> are for quickly emptying +the tanks when necessary, being of a larger bore than +the inlet valves. The inlet pipes <i>H</i> <i>I</i> are placed directly +above the outlet valves, and thus, when required, +before any measurements are taken, the +water can flow directly through the outlet valves, +the pipes terminating only a short distance above +them, away to an auxiliary tank or directly to the +<span class='pagenum'><a name="Page_138" id="Page_138">[138]</a></span>hot-well. Levers <i>K</i> and <i>L</i> fulcrumed at <i>J</i> and <i>J</i> are +connected to the valve spindles by auxiliary levers. +The valve arrangement is such that by pulling down +the lever <i>K</i> the inlet valve <i>D</i> is opened and the inlet +valve <i>E</i> is closed. Again, by pulling down the lever +<i>L</i> the outlet valve <i>F</i> is closed, while the outlet valve +<i>G</i> is also simultaneously closed.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_70" name="FIG_70"></a> + <img src="images/i138.png" + alt="FIG. 70" + title="FIG. 70" + /><br /> +FIG. 70</p> +</div> + +<p>During a consumption test the valves are operated +in the following manner: The lever <i>K</i> is pulled down, +which opens the inlet valve to the first tank and closes +that to the second. The bottom lever <i>L</i>, however, is +lifted, which for the time being opens the outlet valve +<i>F</i>, and incidentally opens the valve <i>G</i>; the latter +valve can; however, for the moment be neglected. +When the turbine is started, and the condensed steam +<span class='pagenum'><a name="Page_139" id="Page_139">[139]</a></span>begins to accumulate in the condenser, the water is +pumped along the pipes and, both the inlet and outlet +valves on the first tank being open, passes through, +without any being deposited in the tank, to the drain. +This may be continued until all conditions are right +for a consumption test and, the time being carefully +noted, lever <i>L</i> is quickly pulled down and the valves +<i>F</i> and <i>G</i> closed. The first tank now gradually fills, +and after a definite period, say fifteen minutes, the +lever <i>K</i> is pushed up, thus diverting the flow into the +second tank. While the latter is filling, the water in +the first tank is measured, and the tank emptied by +a large sluice valve, not shown.</p> + +<p>The operation of alternately filling, measuring, and +emptying the two measuring tanks is thus carried +on until the predetermined time of duration of test +has expired, when the total water as measured in the +tanks, and representing the amount of steam condensed +during that time, is easily found by adding +together the quantities given at each individual +measurement.</p> + +<p>All that are necessary to insure successful results +from a plant similar to this are care and accuracy in +its operation and construction. Undoubtedly in +most cases it is preferable to weigh the condensed +steam instead of measuring the volume passed, and +from that to calculate the weight. If dependence is +being placed upon the volumetric method, it is advisable +to lengthen the duration of the test considerably, +and if possible to measure the feed-water evaporated +at the same time. Such a course, however, would +<span class='pagenum'><a name="Page_140" id="Page_140">[140]</a></span>necessitate little change, and none of a radical nature, +from the arrangement described. Where, however, +the measuring method is adopted, the all-important +feature, requiring on the tester's part careful personal +investigation, is the graduation of the tanks. +It facilitates this operation very considerably when +the receptacles are graduated upon a weight scale. +That is to say, whether or not a vertical scale showing +the actual hight of water be placed inside the tank, +it is advisable to have a separate scale indicating at +once to the attendant the actual contents, by weight, +of the tank at any time. It is the tester's duty to +himself to check the graduation of this latter scale +by weighing the water with which he performs the +operation of checking.</p> + +<p>Apart from the foregoing, there is little to be said +about the measuring apparatus. As has been stated, +accuracy of result depends in this connection, as in +all others, upon careful supervision and sound and +accurate construction, and this the tester can only +positively insure by exhaustive inspection in the one +case and careful deliberation in the conduct of the other.</p> + +<p>It will be readily understood that the procedure—and +this implies some limitations—of a test is to an +extent controlled by the conditions, or particular environment +of the moment. This is strictly true, and +as a consequence it is often impossible, in a maker's +works, for example, to obtain every condition, coinciding +with those specified, which are to be had on +the site of final operation only. For this reason it +<span class='pagenum'><a name="Page_141" id="Page_141">[141]</a></span>would appear best to reserve the final and crucial +test of a machine, which test usually in the operating +sense restricts a prime mover in certain directions +with regard to its auxiliary plant, etc., until the machine +has been finally erected on its site. Obviously, +unless a machine had become more or less standardized, +a preliminary consumption test would be necessary, +but once this primary qualification respecting +consumption had been satisfactorily settled, there +appears to be no reason why exhaustive tests in other +directions should not all be carried out upon the site, +where the conditions for them are so much more favorable.</p> + +<p>When the steam consumption of a steam turbine +is so much higher than the guaranteed quantity, it +usually takes little less than a reconstruction to put +things right. The minor qualifications of a machine, +however, which can be examined into and tested with +greater ease, and usually at considerably less expense, +upon the site, and consequently under specified conditions, +may be advantageously left over until that +site is reached, where it is obvious that any shortcomings +and general deficiency in performance will be +more quickly detected and diagnosed.</p> + + +<h3>Test Loads from the Tester's View-point</h3> + +<p>Before proceeding to describe the points of actual +interest in the consumption test, a few considerations +respecting test loads will be dealt with from the tester's +point of view. Here again we often find ourselves +restricted, to an extent, by the surrounding +<span class='pagenum'><a name="Page_142" id="Page_142">[142]</a></span>conditions. The very first considerations, when undertaking +to carry out a consumption test, should be +devoted to obtaining the steadiest possible +<ins class="correction" title="Transcriber: load?">lead</ins>. It +may be, and is in many cases, that circumstances +are such as to allow a steady electrical load to be +obtained at almost any time. On the other hand an +electrical load of any description is sometimes not +procurable at all, without the installation of a special +plant for the purpose. In such cases a mechanical +friction load, as, for example, that obtained by the +water brake, is sometimes available, or can easily be +procured. Whereas, however, this type of load may +be satisfactory for small machines, it is usually quite +impossible for use with large units, of, say, 5000 kilowatts +and upward. It is seldom, however, that +turbines are made in large sizes for directly driving +anything but electrical plants, although there is every +possibility of direct mechanical driving between large +steam turbines and plants of various descriptions, +shortly coming into vogue, so that usually there exist +some facilities for obtaining an electrical load at both +the maker's works and upon the site of operation.</p> + +<p>One consideration of importance is worth inquiring +into, and this has relation to the largest turbo-generators +supplied for power-station and like purposes. +Obviously, the testing of, say, a 7000-kilowatt alternator +by any standard electrical-testing method must +entail considerable expense, if such a test is to be +carried out in the maker's works. Nor would this +expense be materially decreased by transferring the +operations to the power-station, and there erecting +<span class='pagenum'><a name="Page_143" id="Page_143">[143]</a></span>the necessary electrical plant for obtaining a water +load, or any other installation of sufficient capacity +to carry the required load according to the rated full +capacity of the machine.</p> + +<p>Assuming, then, that there exist no permanent +facilities at either end, namely the maker's works +and the power station, for adequately procuring a +steady electrical-testing load of sufficient capacity, +there still remains, in this instance, an alternative +source of power which is usually sufficiently elastic +to serve all purposes, and this is of course the total +variable load procurable from the station bus-bars. +It is conceivable that one out of a number of machines +running in parallel might carry a perfectly steady +load, the latter being a fraction of a total varying +quantity, leaving the remaining machines to receive +and deal with all fluctuations which might occur. +Even in the event of there being only two machines, +it is possible to maintain the load on one of them +comparatively steady, though the percentage variation +in load on either side of the normal would in the +latter case be greater than in the previous one. This +is accomplished by governor regulation after the +machines have been paralleled. For example, assuming +three turbo-alternators of similar make and capacity +to be running in parallel, each machine carrying +exactly one-third of the total distributed load, it is +fair to regard the governor condition, allowing for +slight mechanical disparities of construction, of all +three machines as being similar; and even in the case +of three machines of different capacity and construction, +<span class='pagenum'><a name="Page_144" id="Page_144">[144]</a></span>the governor conditions when the machines are +paralleled are more or less relatively and permanently +fixed in relation to one another. In other words, +while the variation in load on each machine is the +same, the relative variation in the governor condition +must be constant.</p> + +<p>By a previously mentioned system of governor +regulation, however, it is possible, considering again +for a moment the case of three machines in parallel, +by decreasing the sensitiveness of one governor only, +to accommodate nearly all the total variation in load +by means of the two remaining machines, the unresponsiveness +of the one governor to change in speed +maintaining the load on that machine fairly constant. +By this method, at any rate, the variation in load on +any one machine can be minimized down to, say, 3 +per cent, either side of the normal full load.</p> + +<p>There is another and more positive method by +which a perfectly steady load can be maintained upon +one machine of several running in parallel. This +may be carried out as follows: Suppose, in a station +having a total capacity of 20,000 kilowatts, there are +three machines, two of 6000 kilowatts each, and one +of 8000 kilowatts, and it is desired to carry out a +steady full-load test upon one of the 6000 kilowatts +units. Assuming that the test is to be of six hours' +duration, and that the conditions of load fluctuations +upon the station are well known, the first step to take +is to select a period for the test during which the total +load upon all machines is not likely to fall below, say, +8000 kilowatts. The tension upon the governor +<span class='pagenum'><a name="Page_145" id="Page_145">[145]</a></span>spring of the turbine to be tested must then be adjusted +so that the machine on each peak load is taxed +to its utmost normal capacity; and even when the +station load falls to its minimum, the load from the +particular machine shall not be released sufficiently +to allow it to fall below 6000 kilowatts. Under these +conditions, then, it may be assumed that although +the load on the test machine will vary, it cannot fall +below 6000 kilowatts. Therefore, all that remains +to be done to insure a perfectly steady load equal to +the normal full load of the machine, or 6000 kilowatts, +is to fix the main throttle or governing valve in such +a position that the steam passing through at constant +pressure is just capable of sustaining full speed under +the load required. When this method is adopted, +it is desirable to fix a simple hight-adjusting and locking +mechanism to the governing-valve spindle. The +load as read on the indicating wattmeter can then +be very accurately varied until correct, and farther +varied, if necessary, should any change occur in the +general conditions which might either directly or indirectly +bring about a change of load.</p> + + +<h3>Preparing the Turbine for Testing</h3> + +<p>All preliminary labors connected with a test being +satisfactorily disposed of, it only remains to place the +turbines under the required conditions, and to then +proceed with the test. For the benefit of those inexperienced +in the operation of large turbines, we will +assume that such a machine is about to be started +for the purpose outlined.</p> + +<p><span class='pagenum'><a name="Page_146" id="Page_146">[146]</a></span>It is always advisable to make a strict practice of +getting all the auxiliary plant under way before starting +up the turbine. In handling a turbine plant the +several operations might be carried through in the +following order:</p> + +<ol class="parnn"> +<li>(1) Circulating oil through all bearings and oil chambers.<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a></li> + +<li>(2) Starting of condenser circulating-water pumps, +and continuous circulation of circulating water through +the tubes of condenser.</li> + +<li>(3) Starting of pump delivering condensed steam +from the condenser hot-well to weighing tanks.</li> + +<li>(4) Starting of air pump, vacuum being raised as +high as possible within condenser.</li> + +<li>(5) Sealing of turbine glands, whether of liquid or +steam type, no adjustment of the quantity of sealing +fluid being necessary, however, at this point.</li> + +<li>(6) Adjustment of valves on and leading to the +water-weighing tanks.</li> + +<li>(7) Opening of main exhaust valve or valves between +turbine and condenser.</li> + +<li>(8) Starting up of turbine and slowly running to +speed.</li> + +<li>(9) Application of load, and adjustment of gland-sealing steam.</li> +</ol> + + +<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> In a self-contained system, where the oil pump is usually +driven from the turbine spindle, this would of course be impossible. In +the gravity and allied systems, however, it should always be the first +operation performed. The tests for oil consumption, described +previously, having been carried out, it is assumed that suitable means +have been adopted to restrict the total oil flow through the bearings to +a minimum quantity.</p></div> + +<p>The running to speed of large turbo-alternators +<span class='pagenum'><a name="Page_147" id="Page_147">[147]</a></span>requires considerable care, and should always be +done slowly; that is to say the rate of acceleration +should be slow. It is well known that the vibration +of a heavy unit is accompanied by a synchronous or +non-synchronous vibration of the foundation upon +which it rests. The nearest approach to perfect +synchronism between unit and foundation is obtained +by a gradual rise in speed. A machine run up to +speed too quickly might, after passing the critical +speed, settle down with little visible vibration, but at +a later time, even hours after, suddenly begin vibrating +violently from no apparent cause. The chances +of this occurring are minimized by slow and careful +running to speed.</p> + +<p>Whether the machine being tested is one of a number +running in parallel, or a single unit running on a +steady water load, the latter should in all cases be +thrown on gradually until full load is reached. A +preliminary run of two or three hours—whenever +possible—should then be made, during which ample +opportunity is afforded for regulating the conditions +in accordance with test requirements. The tester +will do well during the last hour of this trial run to +station his recorders at their several posts and, for +a short time at least, to have a complete set of readings +taken at the correct test intervals. This more +particularly applies to the electrical water, superheat +and vacuum readings. In the case of a turbo-alternator +the steadiness obtainable in the electrical load +may determine the frequency of readings taken, both +electrical and otherwise. On a perfectly steady water-tank +<span class='pagenum'><a name="Page_148" id="Page_148">[148]</a></span>load, for example, it may be sufficiently adequate +to read all wattmeters, voltmeters, and ammeters +from standard instruments at from one- to two-minute +intervals. Readings at half-minute intervals, however, +should be taken with a varying load, even when +the variation is only slight.</p> + +<p>The water-measurement readings may of course be +taken at any suitable intervals, the time being to an +extent determined by the size of the measuring tanks +or the capacity of the weighing machine or machines. +When designing the measuring apparatus, the object +should be to minimize, within economical and practical +range, the total number of weighings or measurements +necessary. Consequently, no strict time of +interval between individual weighings or measurements +can be given in this case. It may be said, however, +that it is not desirable to take these at anything +less than five-minute intervals. Under ordinary circumstances +a three- to five-minute interval is sufficient +in the case of all steam-pressure, vacuum—including +mercurial columns and barometer—superheat and +temperature readings.</p> + + +<h3>Gland and Hot-Well Regulation</h3> + +<p>There are two highly important features requiring +more or less constant attention throughout a test, +namely the gland and hot-well regulation. For the +present purpose we may assume that the glands are +supplied with either steam or water for sealing them. +All steam supplied to the turbine obviously goes to +swell the hot-well contents, and to thus increase the +<span class='pagenum'><a name="Page_149" id="Page_149">[149]</a></span>total steam consumption. The ordinary steam gland +is in reality a pressure gland. At both ends of the +turbine casing is an annular chamber, surrounding +the turbine spindle at the point where it projects +through the casing. A number of brass rings on either +side of this chamber encircle the spindle, with only a +very fine running clearance between the latter and +themselves. Steam enters the gland chamber at a +slight pressure, and, when a vacuum exists inside the +turbine casing, tends to flow inward. The pressure, +however, inside the gland is increased until it exceeds +that of the atmosphere outside, and by maintaining +it at this pressure it is obvious that no air can possibly +enter the turbine through the glands, to destroy +the vacuum. The above principle must be borne in +mind during a test upon a turbine having steam-fed +glands. Perhaps the best course to follow—in view +of the economy of gland steam consumption necessary—is +as follows:</p> + +<p>During the preliminary non-test run, full steam is +turned into both glands while the vacuum is being +raised, and maintained until full load has been on +the turbine for some little time. The vacuum will by +this time have probably reached its maximum, and +perhaps fallen to a point slightly lower, at which hight +it may be expected to remain, other conditions also +remaining constant. The gland steam must now be +gradually turned off until the amount of steam vapor +issuing from the glands is almost imperceptible. +This should not lower the vacuum in the slightest +degree. By gradual degrees the gland steam can be +<span class='pagenum'><a name="Page_150" id="Page_150">[150]</a></span>still farther cut down, until no steam vapor at all +can be discerned issuing from the gland boxes. This +reduction should be continued until a point is reached +at which the vacuum is affected, when it must be +stopped and the amount of steam flowing to the gland +again increased very slightly, just enough to bring +the vacuum again to its original hight. The steam +now passing into the glands is the minimum required +under the conditions, and should be maintained +as nearly constant as possible throughout the +test. Practically all steam entering the glands is +drawn into the turbine, and thence to the condenser, +and under the circumstances it may be assumed the +increase in steam consumption arising from this source +is also a minimum.</p> + +<p>There is one mechanical feature which has an important +bearing upon the foregoing question, and +which it is one of the tester's duties to investigate. +This is illustrated in Fig. <a href="#FIG_71">71</a>, which shows a turbine +spindle projecting through the casing. The gland +box is let into the casing as shown. Brass rings <i>A</i> +calked into the gland box encircle the shaft on either +side of the annular steam space <i>S</i>. As the clearance +between the turbine spindle and the rings <i>A</i> is in a +measure instrumental in determining the amount of +steam required to maintain a required pressure inside +the chamber, it is obvious that this clearance should +be minimum. An unnecessarily large clearance means +a proportionally large increase in gland steam consumption +and <i>vice versa</i>.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_71" name="FIG_71"></a> + <img src="images/i151.png" + alt="FIG. 71" + title="FIG. 71" + /><br /> +FIG. 71</p> +</div> + +<p>When the turbine glands are sealed with water, all +<span class='pagenum'><a name="Page_151" id="Page_151">[151]</a></span>water leakage which takes place into the turbine, and +ultimately to the condenser hot-well, must be measured +and subtracted from the hot-well contents at the end of a test.</p> + +<p>The foregoing remarks would not apply to those +cases in which the gland supply is drawn from and +returned to the hot-well, or a pipe leading from the +hot-well. Then no correction would be necessary, +as all water used for gland purposes might be assumed +as being taken from the measuring tanks and returned +again in time for same or next weighing or measurement.</p><p><span class='pagenum'><a name="Page_152" id="Page_152">[152]</a></span></p> + + +<h3>General Considerations</h3> + +<p>There are a few principal elementary points which +it is necessary always to keep in mind during the +conduct of a test. Among these are the effects of +variation in vacuum, superheat, initial steam pressure, +and, as already indicated, in load. There exist +many rules for determining the corrections necessitated +by this variation. For example, it is often +assumed that 9 degrees Fahrenheit, excess or otherwise, +above or below that specified, represents an increase +or reduction in efficiency of about 1 per cent. +It is probable that the percentage increase or decrease +in steam consumption, in the case of superheat, can +be more reliably calculated than in other cases, as, +for example, vacuum; but the increase cannot be said +to be due solely to the variation in superheat. In +other words, the individuality of the particular turbine +being tested always contributes something, however +small this something may be, to the results obtained.</p> + +<p>These remarks are particularly applicable where +vacuum is concerned. Here again rules exist, one of +these being that every additional inch of vacuum +increases the economy of the turbine by something +slightly under half a pound of steam per kilowatt-hour. +But a moment's consideration convinces one +of the utter unreliability of such rules for general +application. It is, for instance, well known that +many machines, when under test, have demonstrated +that the total increase in the water rate is very far +from constant. A machine tested, for example, gave +<span class='pagenum'><a name="Page_153" id="Page_153">[153]</a></span>approximately the following results, the object of the +test being to discover the total increase in the water +rate per inch decrease in vacuum:</p> + +<p>From 27 inches to 26 inches, 4.5 per cent.</p> + +<p>From 26.2 inches to 24.5 inches, 2.5 per cent.</p> + +<p>This illustrates to what an extent the ratio of increase +can vary, and it must be borne in mind that it is very +probable that the variation is different in different +types and sizes of machines.</p> + +<p>There can exist, therefore, no empirical rules of a +reliable nature upon which the tester can base his +deductions. The only way calculated to give satisfaction +is to conduct a series of preliminary tests upon +the turbine undergoing observation, and from these +to deduce all information of the nature required, +which can be permanently recorded in a set of curves +for reference during the final official tests.</p> + +<p>In conclusion, it must be admitted that many published +tests outlining the performances of certain +makes of turbine are unreliable. To determine +honestly the capabilities of any machine in the direction +of steam economy is an operation requiring time, +and unbiased and accurate supervision. By means +of such assets as "floating quantities," short tests +during exceptionally favorable conditions, and disregard +of the vital necessity of running a test under +the proper specified conditions, it is comparatively +easy to obtain results apparently highly satisfactory, +but which under other conditions might be just +the reverse. These considerations are, however, unworthy +of the tester proper.</p> + + + +<hr class="major" /><p><span class='pagenum'><a name="Page_154" id="Page_154">[154]</a></span></p> +<h2><a name="VII_AUXILIARIES_FOR_STEAM_TURBINES6" id="VII_AUXILIARIES_FOR_STEAM_TURBINES6"></a>VII. AUXILIARIES FOR STEAM TURBINES<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a></h2> + +<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> Contributed to <i>Power</i> by Thomas Franklin.</p></div> + + +<h3>The Jet Condenser</h3> + +<p><span class="smcap">The</span> jet condenser illustrated in Fig. <a href="#FIG_72">72</a> is singularly +well adapted for the turbine installation. As the +type has not been so widely adopted as the more +common forms of jet condenser and the surface types, +it may prove of interest to describe briefly its general +construction and a few of its special features in relation +to tests.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_72" name="FIG_72"></a> + <img src="images/i155.png" + alt="FIG. 72" + title="FIG. 72" + /><br /> +FIG. 72</p> +</div> + +<p>Referring to the figure, <i>C</i> is the main condenser +body. Exhaust steam enters at the left-hand side +through the pipe <i>E</i>, condensing water issuing through +the pipe <i>D</i> at the opposite side. Passing through the +short conical pipe <i>P</i>, the condensing water enters +the cylindrical chamber <i>W</i> and falls directly upon +the spraying cone <i>S</i>. The hight of this spraying cone +is determined by the tension upon the spring <i>T</i>, below +the piston <i>R</i>, the latter being connected to the cone +by a spindle <i>L</i>. An increase of the water pressure +inside the chamber <i>W</i> will thus compress the spring, +and the spraying cone being consequently lowered +increases the aperture between it and the sloping +<span class='pagenum'><a name="Page_155" id="Page_155">[155]</a></span>lower wall of the chamber <i>W</i>, allowing a greater volume +of water to be sprayed. The piston <i>R</i> incidentally +prevents water entering the top vapor chamber +<i>V</i>. From the foregoing it can be seen that this condenser +is of the contra-flow type, the entering steam +coming immediately into contact with the sprayed +water. The perforated diaphragm plate <i>F</i> allows +the vapor to rise into the chamber <i>V</i>, from which it +is drawn through the pipe <i>A</i> to the air pump. A +relief valve <i>U</i> prevents an excessive accumulation +<span class='pagenum'><a name="Page_156" id="Page_156">[156]</a></span>of pressure in the vapor chamber, this valve being +obviously of delicate construction, capable of opening +upon a very slight increase of the internal pressure +over that of the atmosphere. Condensed steam and +circulating water are together carried down the pipe +<i>B</i> to the well <i>Z</i>, from which a portion may be carried +off as feed water, and the remainder cooled and passed +through the condenser again. Under any circumstances, +whether the air pump is working or not, a +certain percentage of the vapor in the condenser is +always carried down the pipe <i>B</i>, and this action alone +creates a partial vacuum, thus rendering the work of +the air pump easier. As a matter of fact, a fairly high +vacuum can be maintained with the air pump closed +down, and only the indirect pumping action of the +falling water operating to rarify the contents of the +condenser body. It is customary to place the condenser +forty or more feet above the circulating-water +pump, the latter usually being a few feet below the turbine.</p> + + +<h3>Features Demanding Attention</h3> + +<p>When operating a condenser of this type, the most +important features requiring preliminary inspection +and regulation while running are:</p> + +<ol class="parna"> +<li>(<i>a</i>) Circulating-water regulation.</li> + +<li>(<i>b</i>) Freedom of all mechanical parts of spraying mechanism.</li> + +<li>(<i>c</i>) Relief-valve regulation.</li> + +<li>(<i>d</i>) Water-cooling arrangements.</li> +</ol> + + +<p>The tester will, however, devote his attention to +<span class='pagenum'><a name="Page_157" id="Page_157">[157]</a></span>a practical survey of the condenser and its auxiliaries, +before running operations commence.</p> + +<p>A preliminary vacuum test ought to be conducted +upon the condenser body, and the exhaust piping +between the condenser and turbine. To accomplish +this the circulating-water pipe <i>D</i> can be filled with +water to the condenser level. The relief valve should +also be water-sealed. Any existing leakage can thus +be located and stopped.</p> + +<p>Having made the condenser as tight as possible +within practical limits, vacuum might be again raised +and, with the same parts sealed, allowed to fall slowly +for, say, ten minutes. A similar test over an equal +period may then be conducted with the relief valve +not water-sealed. A comparison of the times taken +for an equal fall of vacuum in inches, under the different +conditions, during the above two tests, will reveal +the extent of the leakage taking place through the +relief valve. It seems superfluous to add that the +fall of vacuum in both the foregoing tests must not +be accelerated in any way, but must be a result simply +of the slight inevitable leakage which is to be found in +every system.</p> + +<p>On a comparatively steady load, and with consequently +only small fluctuation in the volume of steam +to be condensed, the conditions are most favorable +for regulating the amount of circulating water necessary. +Naturally, an excess of water above the required +minimum will not affect the pressure conditions +inside the condenser. It does, however, increase +the quantity of water to be handled from the hot-well, +<span class='pagenum'><a name="Page_158" id="Page_158">[158]</a></span>and incidentally lowers the temperature there, +which, whether the feed-water pass through economizers +or otherwise, is not advisable from an economical +standpoint. Thus there is an economical +minimum of circulating water to be aimed at, and, +as previously stated, it can best be arrived at by running +the turbine under normal load and adjusting +the flow of the circulating water by regulating the +main valve and the tension upon the spring <i>T</i>. Under +abnormal conditions, the breakdown of an air pump, +or the sudden springing of a bad leak, for instance, +the amount of circulating water can be increased by +a farther opening of the main valve if necessary, and +a relaxation of the spring tension by hand; or, the +spring tension might be automatically changed immediately +upon the vacuum falling.</p> + +<p>The absolute freedom of all moving parts of the +spraying mechanism should be one of the tester's +first assurances. To facilitate this, it is customary +to construct the parts, with the exception of the springs, +of brass or some other non-corrosive metal. The +spraying cone must be thoroughly clean in every +channel, to insure a well-distributed stream of water. +Nor is it less important that careful attention be +given to the setting and operation of the relief valve, +as will be seen later. The obvious object of such a +valve is to prevent the internal condenser pressure +ever being maintained much higher than the atmospheric +pressure. A number of carefully designed +rubber flap valves, or one large one, have been found +to act successfully for this purpose, although a +<span class='pagenum'><a name="Page_159" id="Page_159">[159]</a></span>balanced valve of more substantial construction would +appear to be more desirable.</p> + + +<h3>Importance of Relief Valves</h3> + +<p>The question of relief valves in turbine installations +is an important one, and it seems desirable at this +point to draw attention to another necessary relief +valve and its function, namely the turbine atmospheric +valve. As generally understood, this is placed +between the turbine and condenser, and, should the +pressure in the latter, owing to any cause, rise above +that of the atmosphere, it opens automatically and +allows the exhaust steam to flow through it into the +atmosphere, or into another condenser.</p> + +<p>A general diagrammatic arrangement of a steam +turbine, condenser, and exhaust piping is shown in +<ins class="correction" title="original: Fig. 2">Fig. <a href="#FIG_73">73</a></ins>. +Connected to the exhaust pipe <i>B</i>, near to the +condenser, is the automatic atmospheric valve <i>D</i>, +from which leads the exhaust piping <i>E</i> to the atmosphere. +The turbine relief valve is shown at <i>F</i>, and +the condenser relief valve at <i>G</i>. The main exhaust +valve between turbine and condenser is seen at <i>H</i>. +We have here three separate relief valves: one, <i>F</i>, to +prevent excessive pressure in the turbine: the second, +<i>D</i>, an atmospheric valve opening a path to the air, +and, in addition to preventing excessive pressure +accumulating, also helping to keep the temperature +of the condenser body and tubes low; the third, the +condenser relief valve <i>G</i>, which in itself ought to be +capable of exhausting all steam from the turbine, +should occasion demand it.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_73" name="FIG_73"></a> + <img src="images/i162.png" + alt="FIG. 73" + title="FIG. 73" + /><br /> +FIG. 73</p> +</div> + +<p><span class='pagenum'><a name="Page_160" id="Page_160">[160]</a></span>Assuming a plant of this description to be operating +favorably, the conditions would of necessity be +as follows: The valves <i>F</i>, <i>D</i>, and <i>G</i>, all closed; the +valve <i>H</i> open. Suppose that, owing to sudden loss +of circulating water, the vacuum fell to zero. The +condenser would at once fill with steam, a slight pressure +would be set up, and whichever of the three valves +happened to be set to blow off at the lowest pressure +would do so. Now it is desirable that the first valve +to open under such circumstances should be the atmospheric +valve <i>D</i>. This being so, the condenser +would remain full of steam at atmospheric pressure +until the attendant had had time to close the main +hand-or motor-operated exhaust valve <i>H</i>, which he +would naturally do before attempting to regain the +circulation of the condensing water. Again, assume +the installation to be running under the initial conditions, +with the atmospheric valve <i>D</i> and all remaining +valves except <i>H</i> closed.</p> + +<p>Suppose the vacuum again fell to zero from a +similar cause, and, further, suppose the atmospheric +valve <i>D</i> failed to operate automatically. The only +valves now capable of passing the exhaust steam are +the turbine and condenser relief valves <i>F</i> and <i>G</i>. +Inasmuch as the pressures at exhaust in the turbine +proper, on varying load, vary over a considerably +greater range than the small fairly constant absolute +pressures inside the condenser, it is obviously necessary +to allow for this factor in the respective setting +of these two relief valves. In other words, the obvious +deduction is to set the turbine relief valve to +<span class='pagenum'><a name="Page_161" id="Page_161">[161]</a></span>blow off at a higher pressure than the condenser relief +valve, even when considering the question with respect +to condensing conditions only. In this second +hypothetical case, then, with a closed and disabled +atmospheric valve, the exhaust must take place +through the condenser, until the turbine can be shut +down, or the circulating water regained without the +former course being found necessary.</p> + +<p>There is one other remote case which may be +assumed, namely, the simultaneous refusal of both +atmospheric and condenser relief valves to open, upon +the vacuum inside the condenser being entirely lost. +The exhaust would then be blown through the turbine +relief valve <i>F</i>, until the plant could be closed down.</p> + +<p>Although the conditions just cited are highly improbable +in actual practice, it can at once be seen that +to insure the safety of the condenser, absolutely, the +turbine relief valve must be set to open at a comparatively +low pressure, say 40 pounds by gage, or thereabouts. +To set it much lower than this would create +a possibility of its leaking when the turbine was making +a non-condensing run, and when the pressure at the +turbine exhaust end is often above that of the atmosphere. +From every point of view, therefore, it is +advisable to make a minute examination of all relief +valves in a system, and before a test to insure that +these valves are all set to open at their correct relative pressures.</p> + +<p>It must be admitted that the practice of placing a +large relief valve upon a condenser in addition to the +atmospheric exhausting valve is by no means common. +<span class='pagenum'><a name="Page_162" id="Page_162">[162]</a></span>The latter valve, where surface condensing is adopted, +is often thought sufficient, working in conjunction +with a quickly operated main exhaust valve. Similarly, +with a barometric condenser as that illustrated +in Fig. <a href="#FIG_72">72</a>, the atmospheric exhaust valve <i>D</i> (seen in +Fig. <a href="#FIG_73">73</a>) is sometimes dispensed with. This course +is, however, objectionable, for upon a loss of vacuum +in the turbine, all exhaust steam must pass through +the condenser body, or the entire plant be closed down +until the vacuum is regained. The simple construction +of the barometric condenser, however, is in such +an event much to its advantage, and the passage of +the hot steam right through it is not likely to seriously +warp or strain any of its parts, as might probably +happen in the case of a surface condenser.</p> + +<p><span class='pagenum'><a name="Page_163" id="Page_163">[163]</a></span>The question of the advisability of thus adding +to a plant can only be fairly decided when all conditions, +operating and otherwise, are fully known. +For example, if we assume a large turbine to be operating +on a greatly varying load, and exhausting into +a condenser, as that in Fig. <a href="#FIG_72">72</a>, and, further, having +an adequate stand-by to back it up, one's obvious +recommendation would be to equip the installation +with both a condenser relief valve and an atmospheric +valve, in addition, of course, to the main +exhaust valve, which is always placed between the +atmospheric valve and condenser. There are still +other considerations, such as water supply, condition +of circulating water, style of pump, etc., which must +all necessarily have an obvious bearing upon the +settlement of this question; so that generalization is +somewhat out of place, the final design in all cases +depending solely upon general principles and local conditions.</p> + + +<h3>Other Necessary Features of a Test</h3> + +<p>In connection with the condenser, of any type, and +its auxiliaries, there remain a few necessary examinations +and operations to be conducted, if it is desired +to obtain the very best results during the test. It +will be sufficient to just outline them, the method of +procedure being well known, and the requirement +of any strict routine being unnecessary. These include:</p> + +<ol class="parnn"> +<li>(1) A thorough examination of the air-pump, and, +if possible, an equally careful examination of +diagrams<span class='pagenum'><a name="Page_164" id="Page_164">[164]</a></span> +taken from it when running on full load. Also +careful examination of the piping, and of any other +connections between the air pump and condenser, or +other auxiliaries. It will be well in this examination +to note the general "lay" of the air pipes, length, +hight to which they rise above condenser and air +pump, facilities for drainage, etc., as this information +may prove valuable in determining the course necessary +to rectify deficiencies which may later be found +to exist.</li> + +<li>(2) In a surface condenser, inspection of the pumps +delivering condensed steam to the measuring tanks +or hot-well; inspection of piping between the condenser +and the pump, and also between the pump and +measuring tanks. If these pumps are of the centrifugal +type it is essential to insure, for the purposes +of a steam-consumption test, as much regularity of +delivery as possible.</li> + +<li>(3) In the case of a consumption test upon a turbine +exhausting into a barometric condenser, and +where the steam consumed is being measured by the +evaporation in the boiler over the test period, time +must be devoted to the feed-pipes between the feed-water +measuring meter or tank and the boilers. Under +conditions similar to those operating in a plant such +as that shown in Fig. <a href="#FIG_72">72</a>, the necessary boiler feed +might be drawn from the hot-well, the remainder of +the hot-well contents probably being pumped through +water coolers, or towers, for circulating through the +condenser. With the very best system, it is possible +for a slight quantity of oil to leak into the exhaust +<span class='pagenum'><a name="Page_165" id="Page_165">[165]</a></span> +steam, and thence to the hot-well. In its passage, +say along wooden conduits, to the measuring tank or +meter, this water would probably pass through a number +of filters. The efficiency of these must be thoroughly +insured. It is unusual, in those cases where +a simple turbine steam-consumption test is being +carried out, and not an efficiency test of a complete +plant, to pass the measured feed-water through economizers. +Should the latter course, owing to special +conditions, become necessary, a careful examination +of all economizer pipes would be necessary.</li> + +<li>(4) The very careful examination of all thermometer +pockets, steam- and temperature-gage holes, etc., +as to cleanliness, non-accumulation of scale, etc.</li> +</ol> + +<h3>Special Auxiliaries Necessary</h3> + +<p>Having outlined the points of interest and importance +in connection with the more permanent features +of a plant, we arrive at the preparation and fitting of +those special auxiliaries necessary to carry on the test.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_74" name="FIG_74"></a> + <img src="images/i166.png" + alt="FIG. 74" + title="FIG. 74" + /><br /> +FIG. 74</p> +</div> + +<p>It is customary, when carrying out a first test, upon +both prime mover and auxiliaries, to place every important +stage in the expansion in communication with +a gage, so that the various pressures may be recorded +and later compared with the figures of actual requirement. +To do this, in the case of the turbine, it is +necessary to bore holes in the cover leading to the +various expansion chambers, and into each of these +holes to screw a short length of steam pipe, having +preferably a loop in its length, to the other end of +<span class='pagenum'><a name="Page_166" id="Page_166">[166]</a></span>which the gage is attached. Fig. <a href="#FIG_74">74</a> illustrates, diagrammatically, +a complete turbine installation, and +shows the various points along the course taken by +the steam at which it is desirable to place pressure +gages. The figure does not show the high-pressure +steam pipe, nor any of the turbine valves. With +regard to these, it will be desirable to place a steam +gage in the pipe, immediately before the main stop-valve, +and another immediately after it. Any fall +of pressure between the two sides of the valve can thus +be detected. To illustrate this clearly, Fig. <a href="#FIG_75">75</a> is +given, showing the valves of a turbine, and the position +of the gages connected to them. The two gages +<i>E</i> and <i>F</i> on either side of the main stop-valve <i>A</i> are +<span class='pagenum'><a name="Page_167" id="Page_167">[167]</a></span>also shown. The steam after passing through the +valve, which, in the case of small turbines, is hand-operated, +goes in turn through the automatic stop-valve +<i>B</i>, the function of which is to automatically +shut steam off should the turbine attain a predetermined +speed above the normal, the steam strainer <i>C</i>, +and finally through the governing valve <i>D</i> into the +turbine. As shown, gages <i>G</i> and <i>H</i> are also fitted +on either side of the strainer, and these, in conjunction +with gages <i>E</i> and <i>F</i>, will enable any fall in pressure +between the first two valves and the governing valve +to be found. Up to the governing-valve inlet no +throttling of the steam ought to take place under +normal conditions, <i>i.e.</i>, with all valves open, and +consequently any fall in pressure between the steam +inlet and this point must be the result of internal +wire-drawing. By placing the gages as shown, the +extent to which this wire-drawing affects the pressures +obtainable can be discovered.</p> + +<div class="center"> +<p class="caption"> + <a id="FIG_75" name="FIG_75"></a> + <img src="images/i167.png" + alt="FIG. 75" + title="FIG. 75" + /><br /> +FIG. 75</p> +</div> + +<p>On varying and even on normal and steady full +load, the steam is more or less reduced in pressure +after passing through the governing valve <i>D</i>; a gage <i>I</i> +<span class='pagenum'><a name="Page_168" id="Page_168">[168]</a></span>must consequently be placed between the valve, +preferably on the valve itself, and the turbine. Returning +to Fig. <a href="#FIG_74">74</a>, the gages shown are <i>A</i>, <i>B</i>, <i>C</i>, <i>D</i>, +and <i>E</i>, connected to the first, second, third, fourth, +and fifth expansions; also <i>F</i> in the turbine and exhaust +space, where there are no blades, <i>G</i> in the exhaust +pipe immediately before the main exhaust valve <i>E</i> +(see Fig. <a href="#FIG_73">73</a>), and <i>H</i> connected to the condenser. On +condensing full load it is probable that <i>A</i>, <i>B</i>, and <i>C</i> +will all register pressures above the atmosphere, while +gages <i>D</i>, <i>E</i>, <i>F</i>, and <i>G</i> will register pressures below +the atmosphere, being for this purpose vacuum gages. +On the other hand, with a varying load, and consequently +varying initial pressures, one or two of the +gages may register pressure at one moment and vacuum +at another. It will therefore be necessary to +place at these points compound gages capable of +registering both pressure and vacuum. With the +pressures in the various stages constantly varying, +however, a gage is not by any means the most reliable +instrument for recording such variations. The constant +swinging of the finger not only renders accurate +reading at any particular moment both difficult and, +to an extent, unreliable, but, in addition, the accompanying +sudden changes of condition, both of temperature +and pressure, occurring inside the gage tube, +in a comparatively short time permanently warp this +part, and thus altogether destroy the accuracy of +the gage. It is well known that even with the best +steel-tube gages, registering comparatively steady +pressures, this warping of the tube inevitably takes +<span class='pagenum'><a name="Page_169" id="Page_169">[169]</a></span>place. The quicker deterioration of such gage tubes, +when the gage is registering quickly changing pressures, +can therefore readily be conceived, and for +this reason alone it is desirable to have all gages, +whatever the conditions under which they work, +carefully tested and adjusted at short intervals. If +it is desired to obtain reliable registration of the several +pressures in the different expansions of a turbine +running on a varying load, it would therefore seem +advisable to obtain these by some type of external +spring gage (an ordinary indicator has been found to +serve well for this purpose) which the sudden internal +variations in pressure and temperature cannot deleteriously affect.</p> + +<p>In view of the great importance he must attach to +his gage readings, the tester would do well to test +and calibrate and adjust where necessary all the +gages he intends using during a test. This he can do +with a standard gage-testing outfit. By this means +only can he have full confidence in the accuracy of his results.</p> + +<p>In like manner it is his duty personally to supervise +the connecting and arrangement of the gages, +and the preliminary testing for leakage which can +be carried out simultaneously with the vacuum test +made upon the turbine casing.</p> + + +<h3>Where Thermometers are Required</h3> + +<p>Equally important with the foregoing is the necessity +of calibrating and testing of all thermometers +used during a test. Where possible it is advisable +<span class='pagenum'><a name="Page_170" id="Page_170">[170]</a></span>to place new thermometers which have been previously +tested at all points of high temperature. Briefly +running them over, the points at which it is necessary +to place thermometers in the entire system of the +steam and condensing plant are as follows:</p> + +<ol class="parnn"> +<li>(1) A thermometer in the steam pipe on the boiler, +where the pipe leaves the superheater.</li> + +<li>(2) In the steam pipe immediately in front of the +main stop-valve, near point <i>E</i> in Fig. <a href="#FIG_75">75</a>.</li> + +<li>(3) In the main governing valve body (see <i>I</i>, Fig. <a href="#FIG_75">75</a>) +on the inlet side.</li> + +<li>(4) In the main governing valve body on the turbine +side, which will register temperatures of steam +after it has passed through the valve.</li> + +<li>(5) In the steam-turbine high-pressure chamber, +giving the temperature of the steam before it has +passed through any blades.</li> + +<li>(6) In the exhaust chamber, giving the temperature +of steam on leaving the last row of blades.</li> + +<li>(7) In the exhaust pipe near the condenser.</li> + +<li>(8) In the condenser body.</li> + +<li>(9) In the circulating-water inlet pipe close to the condenser.</li> + +<li>(10) In the circulating-water outlet pipe close to the condenser.</li> + +<li>(11) In the air-pump suction pipe close to the condenser.</li> + +<li>(12) In the air-pump suction pipe close to the air pump.</li> +</ol> + +<p>It is not advisable to place at those vital points, +the readings at which directly or indirectly affect the +<span class='pagenum'><a name="Page_171" id="Page_171">[171]</a></span>consumption, two thermometers, say one ordinary +chemical thermometer and one thermometer of the +gage type, thus eliminating the possibility of any +doubt which might exist were only one thermometer placed there.</p> + +<p>There is no apparent reason why one should attempt +to take a series of temperature readings during a +consumption test on varying load. The temperatures +registered under a steady load test can be obtained +with great reliability, but on a varying load, +with constantly changing temperatures at all points, +this is impossible. This is, of course, owing to the +natural sluggishness of the temperature-recording +instruments, of whatever class they belong to, in +responding to changes of condition. As a matter of +fact, the possibility of obtaining correctly the entire +conditions in a system running under greatly varying +loads is very doubtful indeed, and consequently great +reliance cannot be placed upon figures obtained under +such conditions.</p> + +<p>A few simple calculations will reveal to the tester +his special requirements in the direction of measuring +tanks, piping, etc., for his steam consumption test. +Thus, assuming the turbine to be tested to be of 3000 +kilowatt capacity normal load, with a guaranteed +steam consumption of, say, 14.5 pounds per kilowatt-hour, +he calculates the total water rate per hour, +which in this case would be 43,500 pounds, and designs +his weighing or measuring tanks to cope with that +amount, allowing, of course, a marginal tank volume +for overload requirements.</p> + + + +<hr class="major" /> + +<p><span class='pagenum'><a name="Page_172" id="Page_172">[172]</a></span></p> + +<h2><a name="VIII_TROUBLES_WITH_STEAM_TURBINE_AUXILIARIES" + id="VIII_TROUBLES_WITH_STEAM_TURBINE_AUXILIARIES"></a> +VIII. TROUBLES WITH STEAM TURBINE AUXILIARIES<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a> +</h2> + +<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> Contributed to <i>Power</i> by Walter B. Gump.</p></div> + + +<p><span class="smcap">The</span> case about to be described concerns a steam +plant in which there were seven cross-compound +condensing Corliss engines, and two Curtis steam +turbines. The latter were each of 1500-kilowatt +capacity, and were connected to surface condensers, +dry-vacuum pumps, centrifugal, hot-well and circulating +pumps, respectively. In the illustration (Fig. <a href="#FIG_76">76</a>), +the original lay-out of piping is shown in full lines. +Being originally a reciprocating plant it was difficult +to make the allotted space for the turbines suitable +for their proper installation. The trouble which +followed was a perfectly natural result of the failure +to meet the requirements of a turbine plant, and the +description herein given is but one example of a great +many where the executive head of a concern insists +upon controlling the situation without regard to engineering +advice or common sense.</p> + + +<div class="center"> +<p class="caption"> + <a id="FIG_76" name="FIG_76"></a> + <a href="images/i173H.png"> + <img src="images/i173.png" + alt="FIG. 76. TURBINE AUXILIARIES AND PIPING" + title="FIG. 76. TURBINE AUXILIARIES AND PIPING" + /> + </a><br /> +FIG. 76. TURBINE AUXILIARIES AND PIPING</p> +</div> + +<h3>Circulating Pump Fails to Meet Guarantee</h3> + +<p>Observing the plan view, it will be seen that the +condensers for both turbines receive their supply of +<span class='pagenum'><a name="Page_173" id="Page_173">[173]</a></span> +cooling water from the same supply pipe; that is, the +pipes, both suction and discharge, leading to No. 1 +condenser are simply branches from No. 2, which was +installed first without consideration for a second unit. +When No. 1 was installed there was a row of columns +from the basement floor to the main floor extending +in a plane which came directly in front of the condenser. +The column <i>P</i> shown in the plan was so located +as to prevent a direct connection between the +<span class='pagenum'><a name="Page_174" id="Page_174">[174]</a></span>centrifugal circulating pump and the condenser +inlet. The centrifugal pump was direct-connected +to a vertical high-speed engine, and the coupling is +shown at <i>E</i> in the elevation.</p> + +<p>Every possible plan was contemplated to accommodate +the engine and pump without removing any +of the columns, and the arrangement shown was +finally adopted, leaving the column <i>P</i> in its former +place by employing an S-connection from the pump +to the condenser. It should be stated that the pump +was purchased under a guarantee to deliver 6000 gallons +per minute under a head of 50 feet, with an impeller +velocity of 285 revolutions per minute. The +vertical engine to which the pump was connected +proved to be utterly unfit for running at a speed beyond +225 to 230 revolutions per minute, and in addition +the S-bend would obviously reduce the capacity, +even at the proper speed of the impeller.</p> + +<p>Besides these factors there was another feature +even more serious. It was found that when No. 2 +unit was operating No. 1 could not get as great a +quantity of circulating water as when No. 2 was shut +down. This was because No. 2 was drawing most +of the water, and No. 1 received only that which No. 2 +could not pull from the suction pipe <i>A</i>. This will +be clear from the fact that the suction and discharge +pipes for No. 1 were only 16 inches, while those of +No. 2 were 20 inches and 16 inches, respectively. The +condenser for No. 2 had 1000 square feet less cooling +surface than No. 1, which had 6000 square feet and +was supplied with cooling water by means of two +<span class='pagenum'><a name="Page_175" id="Page_175">[175]</a></span>centrifugal pumps of smaller capacity than for No. 1 +and arranged in parallel. These were each driven by +an electric motor, and were termed "The Siamese +Twins," due to the way in which they were connected.</p> + +<p>The load factor of the plant ranged from 0.22 to +0.30, the load being almost entirely lighting, so that +for the winter season the load factor reached the +latter figure. The day load was, therefore, light and +not sufficient to give one turbine more than from +one-fourth to one-third its rated capacity. Under +these conditions No. 1 unit was able to operate much +more satisfactorily than when fully loaded, because +of the fact that the cooling water was more effective. +This was, of course, all used by No. 1 unit when No. 2 +was not operating. At best, however, it was found +that the vacuum could not be made to exceed 24 +inches, and during the peak, with the two turbines +running, the vacuum would often drop to 12 inches. +A vacuum of 16 inches or 18 inches on the peak was +considered good.</p> + + +<h3>An Investigation</h3> + +<p>Severe criticism "rained" heavily upon the engineer +in charge, and complaints were made in reference +to the high oil consumption. An investigation on +the company's part followed, and the firm which +furnished the centrifugal pump and engine was next +in order to receive complaints. Repeated efforts were +made to increase the speed of the vertical engine to +285 revolutions per minute, but such a speed proved +<span class='pagenum'><a name="Page_176" id="Page_176">[176]</a></span>detrimental to the engine, and a lower speed of about +225 revolutions per minute had to be adopted.</p> + +<p>A thorough test on the pump to ascertain its delivery +at various speeds was the next move, and a notched +weir, such as is shown in the elevation, was employed. +The test was made on No. 2 cooling tower, not shown +in the sketch, and showed that barely 3000 gallons +per minute were being delivered to the cooling tower. +While the firm furnishing the pump was willing to +concede that the pump might not be doing all it should, +attention was called to the fact that there might be +some other conditions in connection with the system +which were responsible for the losses. Notable +among these was the hydraulic friction, and when this +feature of the case was presented, the company did +not seem at all anxious to investigate the matter further; +obviously on account of facing a possible necessity +for new piping or other apparatus which might cost something.</p> + +<p>Approximately 34 feet was the static head of water +to be pumped over No. 2 cooling tower. Pressure +gages were connected to the suction, discharge, and +condenser inlet, as shown at <i>G</i>, <i>G'</i> and <i>G''</i> respectively. +When No. 1 unit was operating alone the gage <i>G</i> +showed practically zero, indicating no vacuum in +the suction pipe. Observing the same gage when +No. 2 unit was running, a vacuum as high as 2 pounds +was indicated, showing that No. 2 was drawing more +than its share of cooling water from the main <i>A</i> and +hence the circulating pump for No. 1 was fighting for +all it received. Gage <i>G'</i> indicated a pressure of 21 +<span class='pagenum'><a name="Page_177" id="Page_177">[177]</a></span>pounds, while <i>G''</i> indicated 18.5 pounds, showing a +difference of 2.5 pounds pressure lost in the S-bend. +This is equivalent to a loss of head of nearly 6 feet, +0.43 pound per foot head being the constant employed. +The total head against which the pump worked was therefore</p> + +<div style="position:relative;width:100%"> +<p class="center"><i>G'</i> + <i>G</i> = 21 + 2,</p> +<p style="text-indent:0;">or</p> +<p> +<span style="position:absolute;left:45%"> 23</span><br /> +<span style="position:absolute;left:45%">—— = 53</span><br /> +<span style="position:absolute; left:45%;"> 0.43</span><br /> +</p> +</div> + +<p style="text-indent:0;">feet approximately. Since the static head was 34 +feet, the head lost in friction was evidently</p> + +<div style="position:relative;width:100%"> +<p class="center">53-34 = 19</p> +<p style="text-indent:0;">feet, or</p> +<p> +<span style="position:absolute;left:45%">1900</span><br /> +<span style="position:absolute;left:45%">—— = 36</span><br /> +<span style="position:absolute;left:45%"> 53</span><br /> +</p> +</div> + +<p style="text-indent:0;">per cent., approximately.</p> + + +<h3>Supply of Cooling Water Limited</h3> + +<p>In addition to this the supply of cooling water was +limited, the vacuum being extremely low at just the +time when efficient operation should be had. The +natural result occurred, which was this: As the load +on the turbine increased, the amount of steam issuing +into the condenser increased, +<ins class="correction" title="Transcriber: heating?">beating</ins> the circulating +water to a temperature which the cooling tower (not +in the best condition) was unable to decrease to any +great extent. The vacuum gradually dropped off, +which indicated that the condenser was being filled +with vapor, and in a short time the small centrifugal +<span class='pagenum'><a name="Page_178" id="Page_178">[178]</a></span>tail-pump lost its prime, becoming "vapor bound," +and the vacuum further decreased. The steam which +had condensed would not go into the tail-pump +because of the tendency of the dry-pump to maintain +a vacuum. When a certain point was reached the +dry-vacuum pump started to draw water in its cylinder, +and the unit had to be shut down immediately.</p> + + +<h3>Vapor-bound Pumps</h3> + +<p>As the circulating water gradually rose in temperature +the circulating pump also became "vapor bound," +so that the unit would be tied up for the rest of the +night, as this pump could not be made to draw hot +water. The reason for this condition may be explained +in the following way. When the circulating +pump was operating and there was a suction of 2 +pounds indicated at <i>G</i>, the water was not flowing to +the pump of its own accord, but was being pulled +through by force. This water would flow through +the pump until a point was reached when the water +became hot enough to be converted into vapor, this +occurring at a point where the pressure was sufficiently +reduced to cause the water to boil. Naturally this +point was in the suction pipe and vapor was thus +maintained behind the pump as long as it was operating. +In this case the pump was merely maintaining +a partial vacuum, but not drawing water. After the +vacuum was once lost, by reason of the facts given, +it could not be regained, as the circulating water, +piping and condenser required a considerable period +of time in which to cool.</p> + +<p><span class='pagenum'><a name="Page_179" id="Page_179">[179]</a></span>Before any radical changes were made it was decided +that a man should crawl in the suction pipe <i>A</i>, +and remove such sand, dirt, or any other obstacles +as were believed to cause the friction. After this +had been done and considerable sand had been removed, +tests were resumed with practically the same +results as before. The investigation was continued +and the dry-vacuum pumps were overhauled, as they +had been damaged by water in the cylinders, and +furthermore needed re-boring. In short, the auxiliaries +were restored to the best condition that could +be brought about by the individual improvement +of each piece of apparatus. As this was not the seat +of the trouble, however, the remedy failed to effect +a "cure." It was demonstrated that the steam consumption +of the turbines was greatly increased due +to priming of the boilers, as well as condensation in +the turbine casing; hence, the ills above mentioned +were aggravated.</p> + + +<h3>Changes in Piping</h3> + +<p>After a great deal of argument from the chief engineer, +and the firm which furnished the pump, both +making a strong plea for a change in the piping, the +company accepted the inevitable, and the dotted +portion shows the present layout. The elbow <i>M</i> was +removed, and a tee put in its place to which the +piping <i>D</i> was connected. The circulating pump was +removed to the position shown, and a direct connection +substituted for the S-bend. The discharge pipe +<i>C</i> was carried from No. 1 unit separately, as shown +<span class='pagenum'><a name="Page_180" id="Page_180">[180]</a></span> +in the elevation, and terminated at No. 1 cooling tower +instead of No. 2, which shortened the distance about +60 feet, the total length of pipe (one way) from No. 1 +unit being originally 250 feet. In this way the condensing +equipment was made practically separate for +each turbine, as it should have been in the first place.</p> + +<p>With the new piping a vacuum of 24 inches on the +peak could be reached. While this is far from an efficient +value, yet it is better than the former figure. +The failure to reach a vacuum of 28 inches or better +is due primarily to a lack of cooling water, but an +improvement in this regard could be made by reconstructing +the cooling towers, which at present do +not offer the proper amount of cooling surface. The +screens used were heavy galvanized wire of about 3/16-inch +mesh, which became coated in a short time, and +must be thoroughly cleaned to permit the water to +drop through them. The supply of cooling water +was taken from a 30-inch pipe line several miles long +and fed from a spring. The amount of water varied +considerably and was at times quite insufficient for +the load on the plant. Instead of meeting this condition +with the best apparatus possible, a chain of +difficulties were added to it, with the results given.</p> + + + +<hr class="major" /> +<p><span class='pagenum'><a name="Page_181" id="Page_181">[181]</a></span></p> +<h2><a name="INDEX" id="INDEX"></a>INDEX</h2> + +<div class="index"> + +<ul> +<li>Acceleration, rate of, <a href="#Page_147">147</a> +</li> + +<li>Adjustment, axial, <a href="#Page_65">65</a> + <ul> + <li>making, <a href="#Page_66">66</a></li> + </ul> +</li> + +<li>Air-pump, examining, <a href="#Page_163">163</a> +</li> + +<li>Allis-Chalmers Co. steam turbine, <a href="#Page_41">41</a> +</li> + +<li>Auxiliaries, <a href="#Page_2">2</a>, <a href="#Page_154">154</a> + <ul> + <li>special, <a href="#Page_165">165</a></li> + </ul> +</li> + +<li>Auxiliary plant for consumption test, <a href="#Page_137">137</a> + <ul> + <li>spring on governor dome, <a href="#Page_28">28</a></li> + </ul> +</li> + +<li>Axial adjustment, <a href="#Page_65">65</a> +</li> +</ul> + +<ul> +<li>Baffler, <a href="#Page_36">36</a> + <ul> + <li>functions, <a href="#Page_39">39</a></li> + </ul> +</li> + +<li>Bearings, main, <a href="#Page_69">69</a> +</li> + +<li>Blades, construction details, <a href="#Page_44">44</a> + <ul> + <li>inspecting, <a href="#Page_104">104</a></li> + </ul> +</li> + +<li>Blading, Allis-Chalmers turbine, <a href="#Page_48">48</a> + <ul> + <li>Westinghouse-Parsons turbine, <a href="#Page_59">59</a>, <a href="#Page_92">92</a></li> + </ul> +</li> + +<li>Blueprints, studying, <a href="#Page_11">11</a> +</li> + +<li>Buckets, moving, <a href="#Page_14">14</a> + <ul> + <li>stationary, <a href="#Page_14">14</a></li> + </ul> +</li> + +<li>Bushings, <a href="#Page_36">36</a> +</li> +</ul> + +<ul> +<li>Carbon packing, <a href="#Page_19">19</a> + <ul> + <li>ring, <a href="#Page_20">20</a></li> + </ul> +</li> + +<li>Central gravity oiling system, <a href="#Page_111">111</a> +</li> + +<li>Circulating pump fails to meet guarantee, <a href="#Page_172">172</a> +</li> + +<li>Clearance, <a href="#Page_15">15</a>, <a href="#Page_150">150</a> + <ul> + <li>adjusting, <a href="#Page_18">18</a><span class='pagenum'><a name="Page_182" id="Page_182">[182]</a></span></li> + <li>between moving and stationary buckets, <a href="#Page_4">4</a></li> + <li>gages, <a href="#Page_17">17</a></li> + <li>measuring, <a href="#Page_18">18</a></li> + <li>radial, <a href="#Page_63">63</a></li> + </ul> +</li> + +<li>Comma lashing, <a href="#Page_95">95</a> +</li> + +<li>Condensers, <a href="#Page_108">108</a>, <a href="#Page_131">131</a> + <ul> + <li>jet, <a href="#Page_154">154</a></li> + </ul> +</li> + +<li>Conditions for successful operation, <a href="#Page_105">105</a> +</li> + +<li>Cooling water supply limited, <a href="#Page_177">177</a> +</li> + +<li>Coupling, <a href="#Page_127">127</a> +</li> + +<li>Cover-plate, <a href="#Page_4">4</a> + <ul> + <li>-plate, lowering, <a href="#Page_9">9</a></li> + </ul> +</li> + +<li>Curtis turbine, <a href="#Page_11">11</a> + <ul> + <li>turbine in practice, <a href="#Page_1">1</a></li> + <li>setting valves, <a href="#Page_31">31</a>, <a href="#Page_32">32</a></li> + </ul> +</li> +</ul> + +<ul> +<li>De Laval turbines, <a href="#Page_118">118</a> +</li> + +<li>Draining system, <a href="#Page_105">105</a> +</li> + +<li>Dummy leakage, <a href="#Page_115">115</a> + <ul> + <li>pistons, <a href="#Page_63">63</a>, <a href="#Page_65">65</a></li> + <li>rings, <a href="#Page_43">43</a>, <a href="#Page_113">113</a>, <a href="#Page_114">114</a></li> + </ul> +</li> +</ul> + +<ul> +<li>Equalizing pipes, <a href="#Page_64">64</a> +</li> + +<li>Exhaust end of turbine, <a href="#Page_107">107</a> + <ul> + <li>pipe, <a href="#Page_107">107</a></li> + </ul> +</li> + +<li>Expanding nozzles, <a href="#Page_14">14</a> +</li> +</ul> + +<ul> +<li>Feed-pipes, <a href="#Page_164">164</a> +</li> + +<li>Flow, rate, <a href="#Page_38">38</a> +</li> + +<li>Foundation drawings, <a href="#Page_2">2</a> + <ul> + <li>rings, <a href="#Page_44">44</a>, <a href="#Page_46">46</a></li> + </ul> +</li> + +<li>Fourth-stage wheel, <a href="#Page_14">14</a> +</li> + +<li>Franklin, Thomas, <a href="#Page_112">112</a>, <a href="#Page_137">137</a>, <a href="#Page_154">154</a> +</li> +</ul> + +<ul> +<li>Gages, calibrating and adjusting, <a href="#Page_169">169</a> + <ul> + <li>clearance, <a href="#Page_17">17</a><span class='pagenum'><a name="Page_183" id="Page_183">[183]</a></span></li> + <li>for test work, <a href="#Page_165">165</a></li> + </ul> +</li> + +<li>Generator, <a href="#Page_53">53</a> +</li> + +<li>Glands, examination for scale, <a href="#Page_104">104</a> + <ul> + <li>packing, <a href="#Page_71">71</a>, <a href="#Page_77">77</a></li> + <li>regulation, <a href="#Page_148">148</a></li> + </ul> +</li> + +<li>Governor, Allis-Chalmers turbine, <a href="#Page_48">48</a> + <ul> + <li>Curtis turbine, <a href="#Page_27">27</a>, <a href="#Page_31">31</a></li> + <li>improved, Westinghouse-Parsons turbine, <a href="#Page_83">83</a></li> + <li>-rods, adjusting, <a href="#Page_35">35</a></li> + <li>safety-stop, <a href="#Page_86">86</a></li> + <li>Westinghouse-Parsons turbine, <a href="#Page_80">80</a></li> + </ul> +</li> + +<li>Grinding, <a href="#Page_38">38</a> +</li> + +<li>Guide-bearing, lower, <a href="#Page_9">9</a> +</li> + +<li>Gump, Walter B., <a href="#Page_172">172</a> +</li> +</ul> + +<ul> +<li>Holly draining system, <a href="#Page_106">106</a> +</li> + +<li>Horseshoe shim, <a href="#Page_8">8</a> +</li> + +<li>Hot-well regulation, <a href="#Page_148">148</a> +</li> +</ul> + +<ul> +<li>Inspection, <a href="#Page_103">103</a> +</li> + +<li>Intermediate, <a href="#Page_14">14</a> +</li> +</ul> + +<ul> +<li>Jacking ring, <a href="#Page_8">8</a> +</li> + +<li>Jet condenser, <a href="#Page_154">154</a> +</li> + +<li>Johnson, Fred L., <a href="#Page_1">1</a>, <a href="#Page_31">31</a> +</li> +</ul> + +<ul> +<li>Leakage, <a href="#Page_118">118</a> +</li> + +<li>Load variation, <a href="#Page_144">144</a> +</li> + +<li>Lower guide-bearing, <a href="#Page_9">9</a> +</li> + +<li>Lubrication, <a href="#Page_51">51</a> +</li> +</ul> + +<ul> +<li>Measuring tanks, <a href="#Page_171">171</a> +</li> + +<li>Mechanical valve-gear, <a href="#Page_32">32</a> +</li> +</ul> + +<ul> +<li>Nozzles, expanding, <a href="#Page_14">14</a> +</li> +</ul> + +<ul> +<li>Oil, <a href="#Page_57">57</a>, <a href="#Page_103">103</a>, <a href="#Page_109">109</a><span class='pagenum'><a name="Page_184" id="Page_184">[184]</a></span> + <ul> + <li>amount passing through bearings, <a href="#Page_122">122</a></li> + <li>consumption, high, <a href="#Page_175">175</a></li> + <li>detecting water in, <a href="#Page_122">122</a></li> + <li>pressure, <a href="#Page_122">122</a></li> + <li>-temperature curve, <a href="#Page_123">123</a></li> + </ul> +</li> + +<li>Oil, testing, <a href="#Page_110">110</a> + <ul> + <li>velocity of flow, <a href="#Page_122">122</a></li> + </ul> +</li> + +<li>Oiling, <a href="#Page_87">87</a> + <ul> + <li>system, importance, <a href="#Page_119">119</a></li> + </ul> +</li> + +<li>Operation, Allis-Chalmers turbine, <a href="#Page_54">54</a>, <a href="#Page_55">55</a> + <ul> + <li>successful, <a href="#Page_105">105</a></li> + </ul> +</li> + +<li>Operations in handling turbine plant, <a href="#Page_146">146</a> +</li> + +<li>Overload valve, <a href="#Page_28">28</a> +</li> +</ul> + +<ul> +<li>Packing, carbon, <a href="#Page_19">19</a> + <ul> + <li>glands, <a href="#Page_71">71</a></li> + <li>ring, self-centering, <a href="#Page_14">14</a></li> + </ul> +</li> + +<li>Parsons type of turbine, <a href="#Page_41">41</a> +</li> + +<li>Passage in foundation, <a href="#Page_2">2</a> +</li> + +<li>Peep-holes, <a href="#Page_15">15</a>, <a href="#Page_18">18</a> +</li> + +<li>Piping, <a href="#Page_171">171</a> + <ul> + <li>changing, <a href="#Page_179">179</a></li> + <li>inspection, <a href="#Page_164">164</a></li> + </ul> +</li> + +<li>Pressure, <a href="#Page_63">63</a> + <ul> + <li>gages, <a href="#Page_166">166</a></li> + <li>in glands, <a href="#Page_57">57</a></li> + </ul> +</li> + +<li>Pump, circulating, fails to meet guarantee, <a href="#Page_172">172</a> + <ul> + <li>inspection, <a href="#Page_164">164</a></li> + </ul> +</li> +</ul> + +<ul> +<li>Radial clearance, <a href="#Page_63">63</a> +</li> + +<li>Rateau turbines, <a href="#Page_118">118</a> +</li> + +<li>Relief valves, <a href="#Page_31">31</a> + <ul> + <li>valves, importance, <a href="#Page_159">159</a></li> + </ul> +</li> + +<li>Ring, carbon, <a href="#Page_20">20</a> +</li> + +<li>Rotor, Westinghouse-Parsons turbine, <a href="#Page_59">59</a> +</li> + +<li>Running, <a href="#Page_99">99</a> +</li> +</ul> + +<ul> +<li>Safety-stop, <a href="#Page_22">22</a><span class='pagenum'><a name="Page_185" id="Page_185">[185]</a></span> + <ul> + <li>-stop governor, <a href="#Page_86">86</a></li> + </ul> +</li> + +<li>Saucer steps, <a href="#Page_39">39</a> +</li> + +<li>Screw, step-bearing, <a href="#Page_18">18</a> + <ul> + <li>step-supporting, <a href="#Page_4">4</a></li> + </ul> +</li> + +<li>Separators, <a href="#Page_105">105</a> +</li> + +<li>Setting spindle and cylinder for minimum leakage, <a href="#Page_115">115</a> + <ul> + <li>valves in Curtis turbine, <a href="#Page_31">31</a>, <a href="#Page_32">32</a></li> + </ul> +</li> + +<li>Shaft, holding up while removing support, <a href="#Page_8">8</a> +</li> + +<li>Shield-plate, <a href="#Page_26">26</a>, <a href="#Page_36">36</a> +</li> + +<li>Shim, horseshoe, <a href="#Page_8">8</a> +</li> + +<li>Shroud rings, <a href="#Page_44">44</a>, <a href="#Page_46">46</a> +</li> + +<li>Shrouding on buckets and intermediates, <a href="#Page_18">18</a> +</li> + +<li>Shutting down, <a href="#Page_101">101</a> +</li> + +<li>Special turbine features, <a href="#Page_127">127</a> +</li> + +<li>Spindle, lifting, <a href="#Page_96">96</a> + <ul> + <li>removing, <a href="#Page_104">104</a></li> + </ul> +</li> + +<li>Spraying mechanism, <a href="#Page_158">158</a> +</li> + +<li>Stage valves, <a href="#Page_28">28</a>, <a href="#Page_31">31</a> +</li> + +<li>Starting up, <a href="#Page_54">54</a>, <a href="#Page_95">95</a> +</li> + +<li>Step-bearing, lowering to examine, <a href="#Page_8">8</a> + <ul> + <li>-bearing screw, <a href="#Page_18">18</a></li> + <li>-blocks, <a href="#Page_4">4</a></li> + <li>-lubricant, <a href="#Page_4">4</a></li> + <li>-pressure, <a href="#Page_38">38</a></li> + <li>-supporting screw, <a href="#Page_4">4</a></li> + <li>-water, flow, <a href="#Page_38">38</a></li> + </ul> +</li> + +<li>Stopping turbine, <a href="#Page_56">56</a> +</li> + +<li>Sub-base, <a href="#Page_8">8</a> +</li> + +<li>Superheated steam, <a href="#Page_105">105</a> +</li> +</ul> + +<ul> +<li>Test loads, <a href="#Page_141">141</a> + <ul> + <li>necessary features, <a href="#Page_163">163</a></li> + </ul> +</li> + +<li>Testing oil, <a href="#Page_110">110</a> + <ul> + <li>preparing turbine for, <a href="#Page_145">145</a></li> + <li>steam turbine, <a href="#Page_112">112</a>, <a href="#Page_137">137</a>, <a href="#Page_152">152</a></li> + </ul> +</li> + +<li>Thermometer, calibrating and testing, <a href="#Page_169">169</a><span class='pagenum'><a name="Page_186" id="Page_186">[186]</a></span> + <ul> + <li>oil, <a href="#Page_125">125</a></li> + </ul> +</li> + +<li>Thrust-block, <a href="#Page_118">118</a> +</li> + +<li>Top block, <a href="#Page_4">4</a> +</li> + +<li>Troubles with steam turbine auxiliaries, <a href="#Page_172">172</a> +</li> + +<li>Turbine features, special, <a href="#Page_127">127</a> +</li> +</ul> + +<ul> +<li>Vacuum, <a href="#Page_152">152</a> + <ul> + <li>raising, <a href="#Page_107">107</a></li> + <li>test, <a href="#Page_135">135</a></li> + </ul> +</li> + +<li>Valve-gear, <a href="#Page_83">83</a> + <ul> + <li>-gear, mechanical, <a href="#Page_22">22</a>, <a href="#Page_32">32</a></li> + <li>operation during consumption test, <a href="#Page_138">138</a></li> + <li>overload, <a href="#Page_28">28</a></li> + <li>relief, <a href="#Page_31">31</a></li> + <li>importance, <a href="#Page_159">159</a></li> + <li>setting in Curtis turbine, <a href="#Page_31">31</a>, <a href="#Page_32">32</a></li> + <li>stage, <a href="#Page_28">28</a>,31</li> + </ul> +</li> + +<li>Vapor bound pumps, <a href="#Page_178">178</a> +</li> +</ul> + +<ul> +<li>Water, cooling, limited, <a href="#Page_177">177</a> + <ul> + <li>in oil, detecting, <a href="#Page_122">122</a></li> + <li>-measurement readings, <a href="#Page_148">148</a></li> + <li>pressure, <a href="#Page_101">101</a></li> + <li>service, <a href="#Page_126">126</a></li> + <li>importance, <a href="#Page_119">119</a></li> + <li>tests of condenser, <a href="#Page_133">133</a></li> + <li>used in glands, <a href="#Page_57">57</a>, <a href="#Page_76">76</a></li> + </ul> +</li> + +<li>Westinghouse-Parsons steam turbine, <a href="#Page_58">58</a> +</li> + +<li>Wheels, <a href="#Page_14">14</a> + <ul> + <li>lower or fourth-stage, <a href="#Page_14">14</a></li> + <li>position, <a href="#Page_18">18</a></li> + </ul> +</li> +</ul> +</div> + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of Steam Turbines, by Hubert E. 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Collins + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Steam Turbines + A Book of Instruction for the Adjustment and Operation of + the Principal Types of this Class of Prime Movers + +Author: Hubert E. Collins + +Release Date: January 2, 2009 [EBook #27687] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK STEAM TURBINES *** + + + + +Produced by Chris Curnow, David Cortesi, Brett Fishburne, +Nikolay Fishburne and the Online Distributed Proofreading +Team at https://www.pgdp.net + + + + + + + + + STEAM TURBINES + + + A BOOK OF INSTRUCTION + FOR THE ADJUSTMENT AND OPERATION OF + THE PRINCIPAL TYPES OF THIS + CLASS OF PRIME MOVERS + + + COMPILED AND WRITTEN + BY + + HUBERT E. COLLINS + + FIRST EDITION + Second Impression + + + McGRAW-HILL BOOK COMPANY, Inc. + 239 WEST 39TH STREET, NEW YORK + 6 BOUVERIE STREET, LONDON, E. C. + + Copyright, 1909, by the Hill Publishing Company + + All rights reserved + + + + +TRANSCRIBER'S NOTES + +The authors of this book used the spellings "aline," "gage," and "hight" +for the conventional spellings "align," "gauge," and "height." As they +are used consistently and do not affect the sense, they have been left +unchanged. Obvious typos and misspellings that did not affect the sense +have been silently corrected. The following substantive typographical +errors have also been corrected: "being" to "bearing" (p. 68); "FIG. 50" +to "FIG. 56" (p. 91), and "Fig. 2" to "Fig. 73" (p. 159). Two other +likely errors have been left as transcriber queries: lead/load on p. 142 +and beating/heating on p. 177. + +Superscript numbers are indicated with carets: B^1. Subscript numbers +are indicated with curly braces: P{1} for P-sub-1. + + + + +INTRODUCTION + + +This issue of the Power Handbook attempts to give a compact manual for +the engineer who feels the need of acquainting himself with steam +turbines. To accomplish this within the limits of space allowed, it has +been necessary to confine the work to the description of a few standard +types, prepared with the assistance of the builders. Following this the +practical experience of successful engineers, gathered from the columns +of _Power_, is given. It is hoped that the book will prove of value to +all engineers handling turbines, whether of the described types or not. + + Hubert E. Collins. + New York, April, 1909. + + + + +CONTENTS + + + CHAP. PAGE + + I The Curtis Steam Turbine in Practice 1 + + II Setting the Valves of the Curtis Turbine 31 + + III Allis-Chalmers Steam Turbine 41 + + IV Westinghouse-Parsons Turbine 58 + + V Proper Method of Testing a Steam Turbine 112 + + VI Testing a Steam Turbine 137 + + VII Auxiliaries for Steam Turbines 154 + + VIII Trouble with Steam Turbine Auxiliaries 172 + + + + +I. THE CURTIS STEAM TURBINE IN PRACTICE[1] + +[1] Contributed to _Power_ by Fred L. Johnson. + + +"Of the making of books there is no end." This seems especially true of +steam-turbine books, but the book which really appeals to the operating +engineer, the man who may have a turbine unloaded, set up, put in +operation, and the builders' representative out of reach before the man +who is to operate it fully realizes that he has a new type of prime +mover on his hands, with which he has little or no acquaintance, has not +been written. There has been much published, both descriptive and +theoretical, about the turbine, but so far as the writer knows, there is +nothing in print that tells the man on the job about the details of the +turbine in plain language, and how to handle these details when they +need handling. The operating engineer does not care why the moving +buckets are made of a certain curvature, but he does care about the +distance between the moving bucket and the stationary one, and he wants +to know how to measure that distance, how to alter the clearance, if +necessary, to prevent rubbing. He doesn't care anything about the area +of the step-bearing, but he does want to know the way to get at the +bearing to take it down and put it up again, etc. + +The lack of literature along this line is the writer's apology for what +follows. The Curtis 1500-kilowatt steam turbine will be taken first and +treated "from the ground up." + +On entering a turbine plant on the ground floor, the attention is at +once attracted by a multiplicity of pumps, accumulators and piping. +These are called "auxiliaries" and will be passed for the present to be +taken up later, for though of standard types their use is comparatively +new in power-plant practice, and the engineer will find that more +interruptions of service will come from the auxiliaries than from the +turbine itself. + + +Builders' Foundation Plans Incomplete + +It is impractical for the manufacturers to make complete foundation +drawings, as they are not familiar with the lay-out of pipes and the +relative position of other apparatus in the station. All that the +manufacturers' drawing is intended to do is to show the customer where +it will be necessary for him to locate his foundation bolts and opening +for access to the step-bearing. + +[Illustration: FIG. 1] + +Fig. 1 shows the builders' foundation drawing, with the addition of +several horizontal and radial tubes introduced to give passage for the +various pipes which must go to the middle of the foundation. Entering +through the sides of the masonry they do not block the passage, which +must be as free as possible when any work is to be done on the +step-bearing, or lower guide-bearing. Entering the passage in the +foundation, a large screw is seen passing up through a circular block +of cast iron with a 3/4-inch pipe passing through it. This is the +step-supporting screw. It supports the lower half of the step-bearing, +which in turn supports the entire revolving part of the machine. It is +used to hold the wheels at a proper hight in the casing, and adjust the +clearance between the moving and stationary buckets. The large block +which with its threaded bronze bushing forms the nut for the screw is +called the cover-plate, and is held to the base of the machine by eight +1-1/2-inch cap-screws. On the upper side are two dowel-pins which enter +the lower step and keep it from turning. (See Figs. 2 and 3.) + +[Illustration: FIG. 2] + +[Illustration: FIG. 3] + +The step-blocks are very common-looking chunks of cast iron, as will be +seen by reference to Fig. 4. The block with straight sides (the lower +one in the illustration) has the two dowel holes to match the pins +spoken of, with a hole through the center threaded for 3/4-inch pipe. +The step-lubricant is forced up through this hole and out between the +raised edges in a film, floating the rotating parts of the machine on a +frictionless disk of oil or water. The upper step-block has two +dowel-pins, also a key which fits into a slot across the bottom end of +the shaft. + +[Illustration: FIG. 4] + +The upper side of the top block is counterbored to fit the end of the +shaft. The counterbore centers the block. The dowel-pins steer the key +into the key-way across the end of the shaft, and the key compels the +block to turn with the shaft. There is also a threaded hole in the under +side of the top block. This is for the introduction of a screw which +is used to pull the top block off the end of the shaft. If taken off at +all it must be pulled, for the dowel-pins, key and counterbore are close +fits. Two long bolts with threads the whole length are used if it +becomes necessary to take down the step or other parts of the bottom of +the machine. Two of the bolts holding the cover-plate in place are +removed, these long bolts put in their places and the nuts screwed up +against the plate to hold it while the remaining bolts are removed. + + +How to Lower Step-Bearings to Examine Them + +Now, suppose it is intended to take down the step-bearings for +examination. The first thing to do is to provide some way of holding the +shaft up in its place while we take its regular support from under it. +In some machines, inside the base, there is what is called a "jacking +ring." It is simply a loose collar on the shaft, which covers the holes +into which four plugs are screwed. These are taken out and in their +places are put four hexagonal-headed screws provided for the purpose, +which are screwed up. This brings the ring against a shoulder on the +shaft and then the cover-plate and step may be taken down. + +While all the machines have the same general appearance, there are some +differences in detail which may be interesting. One difference is due to +the sub-base which is used with the oil-lubricated step-bearings. This +style of machine has the jacking ring spoken of, while others have +neither sub-base nor jacking ring, and when necessary to take down the +step a different arrangement is used. + +[Illustration: FIG. 5] + +A piece of iron that looks like a big horseshoe (Fig. 5) is used to hold +the shaft up. The flange that covers the entrance to the exhaust base is +taken off and a man goes in with the horseshoe-shaped shim and an +electric light. Other men take a long-handled wrench and turn up the +step-screw until the man inside the base can push the horseshoe shim +between the shoulder on the shaft and the guide-bearing casing. The men +on the wrench then back off and the horseshoe shim supports the weight +of the machine. When the shim is in place, or the jacking ring set up, +whichever the case may be, the cover-plate bolts may be taken out, the +nuts on the long screws holding the cover in place. + +The 3/4-inch pipe which passes up through the step-screw is taken down +and, by means of the nuts on the long screws, the cover-plate is lowered +about 2 inches. Then through the hole in the step-screw a 3/4-inch rod +with threads on both ends is passed and screwed into the top step; then +the cover-plate is blocked so it cannot rise and, with a nut on the +lower end of the 3/4-inch rod, the top step is pulled down as far as it +will come. The cover-plate is let down by means of the two nuts, and the +top step-block follows. When it is lowered to a convenient hight it can +be examined, and the lower end of the shaft and guide-bearing will be +exposed to view. + +[Illustration: FIG. 6] + +The lower guide-bearing (Fig. 6) is simply a sleeve flanged at one end, +babbitted on the inside, and slightly tapered on the outside where it +fits into the base. The flange is held securely in the base by eight +3/4-inch cap-screws. Between the cap-screw holes are eight holes tapped +to 3/4-inch, and when it is desired to take the bearing down the +cap-screws are taken out of the base and screwed into the threaded holes +and used as jacks to force the guide-bearing downward. Some provision +should be made to prevent the bearing from coming down "on the run," for +being a taper fit it has only to be moved about one-half inch to be +free. Two bolts, about 8 inches long, screwed into the holes that the +cap-screws are taken from, answer nicely, as a drop that distance will +not do any harm, and the bearing can be lowered by hand, although it +weighs about 200 pounds. + +The lower end of the shaft is covered by a removable bushing which is +easily inspected after the guide-bearing has been taken down. If it is +necessary to take off this bushing it is easily done by screwing four +5/8-inch bolts, each about 2 feet long, into the tapped holes in the +lower end of the bushing, and then pulling it off with a jack. (See Fig. +7.) + +Each pipe that enters the passage in the foundation should be connected +by two unions, one as close to the machine as possible and the other +close to the foundation. This allows the taking down of all piping in +the passage completely and quickly without disturbing either threads or +lengths. + +[Illustration: FIG. 7] + + +Studying the Blueprints + +Fig. 8 shows an elevation and part-sectional view of a 1500-kilowatt +Curtis steam turbine. If one should go into the exhaust base of one of +these turbines, all that could be seen would be the under side of the +lower or fourth-stage wheel, with a few threaded holes for the +balancing plugs which are sometimes used. The internal arrangement is +clearly indicated by the illustration, Fig. 8. It will be noticed that +each of the four wheels has an upper and a lower row of buckets and that +there is a set of stationary buckets for each wheel between the two rows +of moving buckets. These stationary buckets are called intermediates, +and are counterparts of the moving buckets. Their sole office is to +redirect the steam which has passed through the upper buckets into the +lower ones at the proper angle. + +[Illustration: FIG. 8. ELEVATION AND PART-SECTIONAL VIEW OF A +1500-KILOWATT CURTIS TURBINE] + +The wheels are kept the proper distance apart by the length of hub, and +all are held together by the large nut on the shaft above the upper +wheel. Each wheel is in a separate chamber formed by the diaphragms +which rest on ledges on the inside of the wheel-case, their weight and +steam pressure on the upper side holding them firmly in place and making +a steam-tight joint where they rest. At the center, where the hubs pass +through them, there is provided a self-centering packing ring (Fig. 9), +which is free to move sidewise, but is prevented from turning, by +suitable lugs. This packing is a close running fit on the hubs of the +wheel and is provided with grooves (plainly shown in Fig. 9) which break +up and diminish the leakage of steam around each hub from one stage to +the next lower. Each diaphragm, with the exception of the top one, +carries the expanding nozzles for the wheel immediately below. + +[Illustration: FIG. 9] + +The expanding nozzles and moving buckets constantly increase in size and +number from the top toward the bottom. This is because the steam volume +increases progressively from the admission to the exhaust and the entire +expansion is carried out in the separate sets of nozzles, very much as +if it were one continuous nozzle; but with this difference, not all of +the energy is taken out of the steam in any one set of nozzles. The idea +is to keep the velocity of the steam in each stage as nearly constant as +possible. The nozzles in the diaphragms and the intermediates do not, +except in the lowest stage, take up the entire circumference, but are +proportioned to the progressive expansion of steam as it descends toward +the condenser. + + +Clearance + +While the machine is running it is imperative that there be no rubbing +contact between the revolving and stationary parts, and this is provided +for by the clearance between the rows of moving buckets and the +intermediates. Into each stage of the machine a 2-inch pipe hole is +drilled and tapped. Sometimes this opening is made directly opposite a +row of moving buckets as in Fig. 10, and sometimes it is made opposite +the intermediate. When opposite a row of buckets, it will allow one to +see the amount of clearance between the buckets and the intermediates, +and between the buckets and the nozzles. When drilled opposite the +intermediates, the clearance is shown top and bottom between the buckets +and intermediates. (See Fig. 11.) This clearance is not the same in all +stages, but is greatest in the fourth stage and least in the first. The +clearances in each stage are nearly as follows: First stage, 0.060 to +0.080; second stage, 0.080 to 0.100; third stage, 0.080 to 0.100; fourth +stage, 0.080 to 0.200. These clearances are measured by what are called +clearance gages, which are simply taper slips of steel about 1/2-inch +wide accurately ground and graduated, like a jeweler's ring gage, by +marks about 1/2-inch apart; the difference in thickness of the gage is +one-thousandth of an inch from one mark to the next. + +[Illustration: FIG. 10] + +[Illustration: FIG. 11] + +To determine whether the clearance is right, one of the 2-inch plugs is +taken out and some marking material, such as red lead or anything that +would be used on a surface plate or bearing to mark the high spots is +rubbed on the taper gage, and it is pushed into the gap between the +buckets and intermediates as far as it will go, and then pulled out, the +marking on the gage showing just how far in it went, and the nearest +mark giving in thousandths of an inch the clearance. This is noted, the +marking spread again, and the gage tried on the other side, the +difference on the gage showing whether the wheel is high or low. +Whichever may be the case the hight is corrected by the step-bearing +screw. The wheels should be placed as nearly in the middle of the +clearance space as possible. By some operators the clearance is adjusted +while running, in the following manner: With the machine running at full +speed the step-bearing screw is turned until the wheels are felt or +heard to rub lightly. The screw is marked and then turned in the +opposite direction until the wheel rubs again. Another mark is made on +the screw and it is then turned back midway between the two marks. +Either method is safe if practiced by a skilful engineer. In measuring +the clearance by the first method, the gage should be used with care, as +it is possible by using too much pressure to swing the buckets and get +readings which could be misleading. To an inexperienced man the taper +gages would seem preferable. In the hands of a man who knows what he is +doing and how to do it, a tapered pine stick will give as satisfactory +results as the most elaborate set of hardened and ground clearance +gages. + +Referring back to Fig. 11, at A is shown one of the peep-holes opposite +the intermediate in the third stage wheel for the inspection of +clearance. The taper clearance gage is inserted through this hole both +above and below the intermediate, and the distance which it enters +registers the clearance on that side. This sketch also shows plainly how +the shrouding on the buckets and the intermediates extends beyond the +sharp edges of the buckets, protecting them from damage in case of +slight rubbing. In a very few cases wheels have been known to warp to +such an extent from causes that were not discovered until too late, that +adjustment would not stop the rubbing. In such cases the shrouding has +been turned or faced off by a cutting-off tool used through the +peep-hole. + + +Carbon Packing Used + +Where the shaft passes through the upper head of the wheel-case some +provision must be made to prevent steam from the first stage escaping. +This is provided for by carbon packing (Fig. 12), which consists of +blocks of carbon in sets in a packing case bolted to the top head of the +wheel-case. There are three sets of these blocks, and each set is made +of two rings of three segments each. One ring of segments breaks joints +with its mate in the case, and each set is separated from the others by +a flange in the case in which it is held. In some cases the packing is +kept from turning by means of a link, one end of which is fastened to +the case and the other to the packing holder. Sometimes light springs +are used to hold the packing against the shaft and in some the pressure +of steam in the case does this. There is a pipe, also shown in Fig. 12, +leading from the main line to the packing case, the pressure in the pipe +being reduced. The space between the two upper sets of rings is drained +to the third stage by means of a three-way cock, which keeps the balance +between the atmosphere and packing-case pressure. The carbon rings are +fitted to the shaft with a slight clearance to start with, and very soon +get a smooth finish, which is not only practically steam-tight but +frictionless. + +[Illustration: FIG. 12] + +The carbon ring shown in Fig. 12 is the older design. The segments are +held against the flat bearing surface of the case by spiral springs set +in brass ferrules. The circle is held together by a bronze strap screwed +and drawn together at the ends by springs. Still other springs press +the straps against the surface upon which the carbon bears, cutting off +leaks through joints and across horizontal surfaces of the carbon. The +whole ring is prevented from turning by a connecting-rod which engages a +pin in the hole, like those provided for the springs. + +[Illustration: FIG. 13] + +[Illustration: FIG. 14] + +[Illustration: FIG. 15] + +[Illustration: FIG. 16] + + +The Safety-stop + +There are several designs of safety-stop or speed-limit devices used +with these turbines, the simplest being of the ring type shown in Fig. +13. This consists of a flat ring placed around the shaft between the +turbine and generator. The ring-type emergencies are now all adjusted so +that they normally run concentric with the shaft, but weighted so that +the center of gravity is slightly displaced from the center. The +centrifugal strain due to this is balanced by helical springs. But when +the speed increases the centrifugal force moves the ring into an +eccentric position, when it strikes a trigger and releases a weight +which, falling, closes the throttle and shuts off the steam supply. The +basic principle upon which all these stops are designed is the same--the +centrifugal force of a weight balanced by a spring at normal speed. +Figs. 14, 15, and 16 show three other types. + + +The Mechanical Valve-Gear + +Fig. 17 shows plainly the operation of the mechanical valve-gear. The +valves are located in the steam chests, which are bolted to the top of +the casing directly over the first sets of expansion nozzles. The +chests, two in number, are on opposite sides of the machine. The +valve-stems extend upward through ordinary stuffing-boxes, and are +attached to the notched cross-heads by means of a threaded end which is +prevented from screwing in or out by a compression nut on the lower end +of the cross-head. Each cross-head is actuated by a pair of +reciprocating pawls, or dogs (shown more plainly in the enlarged view, +Fig. 18), one of which opens the valve and the other closes it. The +several pairs of pawls are hung on a common shaft which receives a +rocking motion from a crank driven from a worm and worm-wheel by the +turbine shaft. The cross-heads have notches milled in the side in +which the pawls engage to open or close the valve, this engagement +being determined by what are called shield-plates, A (Fig. 18), which +are controlled by the governor. These plates are set, one a little +ahead of the other, to obtain successive opening or closing of the +valves. When more steam is required the shield plate allows the proper +pawl to fall into its notch in the cross-head and lift the valve from +its seat. If less steam is wanted the shield-plate rises and allows the +lower pawl to close the valve on the down stroke. + +[Illustration: FIG. 17] + +[Illustration: FIG. 18] + +The valves, as can easily be seen, are very simple affairs, the steam +pressure in the steam chest holding the valve either open or shut until +it is moved by the pawl on the rock-shaft. The amount of travel on the +rock-shaft is fixed by the design, but the proportionate travel above +and below the horizontal is controlled by the length of the +connecting-rods from the crank to the rock-shaft. There are besides the +mechanical valve-gear the electric and hydraulic, but these will be left +for a future article. + + +The Governor + +The speed of the machine is controlled by the automatic opening and +closing of the admission valves under the control of a governor (Fig. +19), of the spring-weighted type attached directly to the top end of the +turbine shaft. The action of the governor depends on the balance of +force exerted by the spring, and the centrifugal effort of the +rectangular-shaped weights at the lower end; the moving weights acting +through the knife-edge suspension tend to pull down the lever against +the resistance of the heavy helical spring. The governor is provided +with an auxiliary spring on the outside of the governor dome for varying +the speed while synchronizing. The tension of the auxiliary spring is +regulated by a small motor wired to the switchboard. This spring should +be used only to correct slight changes in speed. Any marked change +should be corrected by the use of the large hexagonal nut in the upper +plate of the governor frame. This nut is screwed down to increase the +speed, and upward to decrease it. + +[Illustration: FIG. 19] + + +The Stage Valves + +Fig. 20 represents one of the several designs of stage valve, sometimes +called the overload valve, the office of which is to prevent too high +pressure in the first stage in case of a sudden overload, and to +transfer a part of the steam to a special set of expanding nozzles over +the second-stage wheel. This valve is balanced by a spring of adjustable +tension, and is, or can be, set to open and close within a very small +predetermined range of first-stage pressure. The valve is _intended_ to +open and close instantly, and to supply or cut off steam from the second +stage, without affecting the speed regulation or economy of operation. +If any leaking occurs past the valve it is taken care of by a drip-pipe +to the third stage. + +[Illustration: FIG. 20] + +The steam which passes through the automatic stage valves and is +admitted to the extra set of nozzles above the second-stage wheel acts +upon this wheel just the same as the steam which passes through the +regular second-stage nozzles; i.e., all the steam which goes through the +machine tends to hasten its speed, or, more accurately, does work and +_maintains_ the speed of the machine. + + + + +II. SETTING THE VALVES OF THE CURTIS TURBINE[2] + +[2] Contributed to _Power_ by F. L. Johnson. + + +Under some conditions of service the stage valve in the Curtis turbine +will not do what it is designed to do. It is usually attached to the +machine in such manner that it will operate with, or a little behind, in +the matter of time, the sixth valve. The machine is intended to carry +full load with only the first bank of five valves in operation, with +proper steam pressure and vacuum. If the steam pressure is under 150 +pounds, or the vacuum is less than 28 inches, the sixth valve may +operate at or near full load, and also open the stage valve and allow +steam to pass to the second-stage nozzles at a much higher rate of speed +than the steam which has already done some work in the first-stage +wheel. The tendency is to accelerate unduly the speed of the machine. +This is corrected by the governor, but the correction is usually carried +too far and the machine slows down. With the stage valve in operation, +at a critical point the regulation is uncertain and irregular, and its +use has to be abandoned. The excess first-stage pressure will then be +taken care of by the relief valve, which is an ordinary spring safety +valve (not pop) which allows the steam to blow into the atmosphere. + +The mechanical valve-gear does not often get out of order, but sometimes +the unexpected happens. The shop man may not have properly set up the +nuts on the valve-stems; or may have fitted the distance bushings +between the shield plates too closely; the superheat of the steam may +distort the steam chest slightly and produce friction that will +interfere with the regulation. If any of the valve-stems should become +loose in the cross-heads they may screw themselves either in or out. If +screwed out too far, the valve-stem becomes too long and the pawl in +descending will, after the valve is seated, continue downward until it +has broken something. If screwed in, the cross-head will be too low for +the upper pawl to engage and the valve will not be opened. This second +condition is not dangerous, but should be corrected. The valve-stems +should be made the right length, and all check-nuts set up firmly. If +for any purpose it becomes necessary to "set the valves" on a +1500-kilowatt mechanical gear, the operator should proceed in the +following manner. + + +Setting the Valves of a 1500-Kilowatt Curtis Turbine + +We will consider what is known as the "mechanical" valve-gear, with two +sets of valves, one set of five valves being located on each side of the +machine. + +[Illustration: FIG. 21] + +In setting the valves we should first "throw out" all pawls to avoid +breakage in case the rods are not already of proper length, holding the +pawls out by slipping the ends of the pawl springs over the points of +the pawls, as seen in Fig. 21. Then turn the machine slowly by hand +until the pawls on one set of valves are at their highest point of +travel, then with the valves wide open adjust the drive-rods, i.e., the +rods extending from the crank to the rock-shaft, so that there is 1/32 +of an inch clearance (shown dotted in Fig. 17, Chap. I) at the point of +opening of the pawls when they are "in." (See Fig. 22.) Then set up the +check-nuts on the drive-rod. Turn the machine slowly, until the pawls +are at their lowest point of travel. Then, with the valves closed, +adjust each _valve-stem_ to give 1/32 of an inch clearance at the point +of closing of the pawls when they are "in," securely locking the +check-nut as each valve is set. Repeat this operation on the other side +of the machine and we are ready to adjust the governor-rods. (Valves +cannot be set on both sides of the machine at the same time, as the +pawls will not be in the same relative position, due to the angularity +of the drive-rods.) + +[Illustration: FIG. 22] + +Next, with the turbine running, and the synchronizing spring in +mid-position, adjust the governor-rods so that the turbine will run at +the normal speed of 900 revolutions per minute when working on the fifth +valve, and carrying full load. The governor-rods for the other side of +the turbine (controlling valves Nos. 6 to 10) should be so adjusted that +the speed change between the fifth and sixth valves will not be more +than three or four revolutions per minute. + +The valves of these turbines are all set during the shop test and the +rods trammed with an 8-inch tram. Governors are adjusted for a speed +range of 2 per cent. between no load and full load (1500 kilowatt), or 4 +per cent. between the mean speeds of the first and tenth valves (no load +to full overload capacity). + +The rods which connect the governor with the valve-gear have ordinary +brass ends or heads and are adjusted by right-and-left threads and +secured by lock-nuts. They are free fits on the pins which pass through +the heads, and no friction is likely to occur which will interfere with +the regulation, but too close work on the shield-plate bushings, or a +slight warping of the steam chest, will often produce friction which +will seriously impair the regulation. If it is noticed that the +shield-plate shaft has any tendency to oscillate in unison with the +rock-shaft which carries the pawls, it is a sure indication that the +shield-plates are not as free as they should be, and should be attended +to. The governor-rod should be disconnected, the pawls thrown out and +the pawl strings hooked over the ends. + +The plates should then be rocked up and down by hand and the friction at +different points noted. The horizontal rod at the back of the valve-gear +may be loosened and the amount of end play of each individual +shield-plate noticed and compared with the bushings on the horizontal +rod at the back which binds the shield-plates together. If the plates +separately are found to be perfectly free they may be each one pushed +hard over to the right or left and wedged; then each bushing tried in +the space between the tail-pieces of the plates. It will probably be +found that the bushings are not of the right length, due to the +alteration of the form of the steam chest by heat. It will generally be +found also that the bushings are too short, and that the length can be +corrected by very thin washers of sheet metal. It has been found in some +instances that the thin bands coming with sectional pipe covering were +of the right thickness. + +After the length of the bushings is corrected the shield-plates may be +assembled, made fast and tested by rocking them up and down, searching +for signs of sticking. If none occurs, the work has been correctly done, +and there will be no trouble from poor regulation due to friction of the +shield-plates. + + +The Baffler + +The water which goes to the step-bearing passes through a baffler, the +latest type of which is shown by Fig. 23. It is a device for +restricting the flow of water or oil to the step- and guide-bearing. The +amount of water necessary to float the machine and lubricate the +guide-bearing having been determined by calculation and experiment, the +plug is set at that point which will give the desired flow. The plug is +a square-threaded worm, the length of which and the distance which it +enters the barrel of the baffler determining the amount of flow. The +greater the number of turns which the water must pass through in the +worm the less will flow against the step-pressure. + +[Illustration: FIG. 23] + +The engineers who have settled upon the flow and the pressure decided +that a flow of from 4-1/2 to 5-1/2 gallons per minute and a +step-pressure of from 425 to 450 pounds is correct. These factors are so +dependent upon each other and upon the conditions of the step-bearing +itself that they are sometimes difficult to realize in every-day work; +nor is it necessary. If the machine turns freely with a lower pressure +than that prescribed by the engineers, there is no reason for raising +this pressure; and there is only one way of doing it without reducing +the area of the step-bearing, and that is by obstructing the flow of +water in the step-bearing itself. + +A very common method used is that of grinding. The machine is run at +about one-third speed and the step-water shut off for 15 or 20 seconds. +This causes grooves and ridges on the faces of the step-bearing blocks, +due to their grinding on each other, which obstruct the flow of water +between the faces and thus raises the pressure. It seems a brutal way of +getting a scientific result, if the result desired can be called +scientific. The grooving and cutting of the step-blocks will not do any +harm, and in fact they will aid in keeping the revolving parts of the +machine turning about its mechanical center. + +The operating engineer will be very slow to see the utility of the +baffler, and when he learns, as he will sometime, that the turbine will +operate equally well with a plug out as with it in the baffler, he will +be inclined to remove the baffler. It is true that with one machine +operating on its own pump it is possible to run without the baffler, +and it is also possible that in some particular case two machines having +identical step-bearing pressures might be so operated. The baffler, +however, serves a very important function, as described more fully as +follows: It tends to steady the flow from the pump, to maintain a +constant oil film as the pressure varies with the load, and when several +machines are operating on the same step-bearing system it is the only +means which fixes the flow to the different machines and prevents one +machine from robbing the others. Therefore, even if an engineer felt +inclined to remove the baffler he would be most liable to regret taking +such a step. + +If the water supply should fail from any cause and the step-bearing +blocks rub together, no great amount of damage will result. The machine +will stop if operated long under these conditions, for if steam pressure +is maintained the machine will continue in operation until the buckets +come into contact, and if the step-blocks are not welded together the +machine may be started as soon as the water is obtained. If vibration +occurs it will probably be due to the rough treatment of the +step-blocks, and may be cured by homeopathic repeat-doses of grinding, +say about 15 seconds each. If the step-blocks are welded a new pair +should be substituted and the damaged ones refaced. + +Some few experimental steps of spherical form, called "saucer" steps, +have been installed with success (see Fig. 24). They seem to aid the +lower guide-bearing in keeping the machine rotating about the mechanical +center and reduce the wear on the guide-bearing. In some instances, +too, cast-iron bushings have been substituted for bronze, with marked +success. There seems to be much less wear between cast-iron and babbitt +metal than between bronze and babbitt metal. The matter is really worth +a thorough investigation. + +[Illustration: FIG. 24] + + + + +III. ALLIS-CHALMERS COMPANY STEAM TURBINE + + +In Fig. 25 may be seen the interior construction of the steam turbine +built by Allis-Chalmers Co., of Milwaukee, Wis., which is, in general, +the same as the well-known Parsons type. This is a plan view showing the +rotor resting in position in the lower half of its casing. + +[Illustration: FIG. 25] + +Fig. 26 is a longitudinal cross-section cut of rotor and both lower and +upper casing. Referring to Fig. 26 the steam comes in from the +steam-pipe at C and passes through the main throttle or regulating valve +D, which is a balanced valve operated by the governor. Steam enters the +cylinder through the passage E. + +Turning in the direction of the bearing A, it passes through alternate +stationary and revolving rows of blades, finally emerging at F and +going out by way of G to the condenser or to atmosphere. H, J, and K +represent three stages of blading. L, M, and Z are the balance pistons +which counterbalance the thrust on the stages H, J, and K. O and Q are +equalizing pipes, and for the low-pressure balance piston similar +provision is made by means of passages (not shown) through the body of +the spindle. + +[Illustration: FIG. 26] + +R indicates a small adjustable collar placed inside the housing of the +main bearing B to hold the spindle in a position where there will be +such a clearance between the rings of the balance pistons and those of +the cylinder as to reduce the leakage of steam to a minimum and at the +same time prevent actual contact under varying temperature. + +At S and T are glands which provide a water seal against the inleakage +of air and the outleakage of steam. U represents the flexible coupling +to the generator. V is the overload or by-pass valve used for admitting +steam to intermediate stage of the turbine. W is the supplementary +cylinder to contain the low-pressure balance piston. X and Y are +reference letters used in text of this chapter to refer to equalizing of +steam pressure on the low-pressure stage of the turbine. The first point +to study in this construction is the arrangement of "dummies" L, M, and +Z. These dummy rings serve as baffles to prevent steam leakage past the +pistons, and their contact at high velocity means not only their own +destruction, but also damage to or the wrecking of surrounding parts. A +simple but effective method of eliminating this difficulty is found in +the arrangement illustrated in this figure. The two smaller balance +pistons, L and M, are allowed to remain on the high-pressure end; but +the largest piston, Z, is placed upon the low-pressure end of the rotor +immediately behind the last ring of blades, and working inside of the +supplementary cylinder W. Being backed up by the body of the spindle, +there is ample stiffness to prevent warping. This balance piston, which +may also be plainly seen in Fig. 25, receives its steam pressure from +the same point as the piston M, but the steam pressure, equalized with +that on the third stage of the blading, X, is through holes in the webs +of the blade-carrying rings. Entrance to these holes is through the +small annular opening in the rotor, visible in Fig. 25 between the +second and third barrels. As, in consequence of varying temperatures, +there is an appreciable difference in the endwise expansion of the +spindle and cylinder, the baffling rings in the low-pressure balance +piston are so made as to allow for this difference. The high-pressure +end of the spindle being held by the collar bearing, the difference in +expansion manifests itself at the low-pressure end. The labyrinth +packing of the high-pressure and intermediate pistons has a small axial +and large radial clearance, whereas the labyrinth packing of the piston +Z has, vice versa, a small radial and large axial clearance. Elimination +of causes of trouble with the low-pressure balance piston not only makes +it possible to reduce the diameter of the cylinder, and prevent +distortion, but enables the entire spindle to be run with sufficiently +small clearance to obviate any excessive leakage of steam. + + +Detail of Blade Construction + +In this construction the blades are cut from drawn stock, so that at its +root it is of angular dovetail shape, while at its tip there is a +projection. To hold the roots of the blades firmly, a foundation ring is +provided, as shown at A in Fig. 27. This foundation ring is first formed +to a circle of the proper diameter, and then slots are cut in it. These +slots are accurately spaced and inclined to give the right pitch and +angle to the blades (Fig. 28), and are of dovetail shape to receive the +roots of the blades. The tips of the blades are substantially bound +together and protected by means of a channel-shaped shroud ring, +illustrated in Fig. 31 and at B in Fig. 27. Fig. 31 shows the cylinder +blading separate, and Fig. 27 shows both with the shrouding. In these, +holes are punched to receive the projections on the tips of the +blades, which are rivetted over pneumatically. + +[Illustration: FIG. 27] + +The foundation rings themselves are of dovetail shape in cross-section, +and, after receiving the roots of the blades, are inserted in dovetailed +grooves in the cylinder and rotor, where they are firmly held in place +by keypieces, as may be seen at C in Fig. 27. Each keypiece, when driven +in place, is upset into an undercut groove, indicated by D in Fig. 27, +thereby positively locking the whole structure together. Each separate +blade is firmly secured by the dovetail shape of the root, which is held +between the corresponding dovetailed slot in the foundation ring and the +undercut side of the groove. + +[Illustration: FIG. 28] + +Fig. 29, from a photograph of blading fitted in a turbine, illustrates +the construction, besides showing the uniform spacing and angles of the +blades. + +[Illustration: FIG. 29] + +The obviously thin flanges of the shroud rings are purposely made in +that way, so that, in case of accidental contact between revolving and +stationary parts, they will wear away enough to prevent the blades +from being ripped out. This protection, however, is such that to rip +them out a whole half ring of blades must be sheared off at the roots. +The strength of the blading, therefore, depends not upon the strength of +an individual blade, but upon the combined shearing strength of an +entire ring of blades. + +[Illustration: FIG. 30] + +The blading is made up and inserted in half rings, and Fig. 30 shows two +rings of different sizes ready to be put in place. Fig. 31 shows a +number of rows of blading inserted in the cylinder of an Allis-Chalmers +steam turbine, and Fig. 32 gives view of blading in the same turbine +after nearly three years' running. + +[Illustration: FIG. 31] + +[Illustration: FIG. 32] + + +The Governor + +Next in importance to the difference in blading and balance piston +construction, is the governing mechanism used with these machines. This +follows the well-known Hartung type, which has been brought into +prominence, heretofore largely in connection with hydraulic turbines; +and the governor, driven directly from the turbine shaft by means of cut +gears working in an oil bath, is required to operate the small, balanced +oil relay-valve only, while the two steam valves, main and by-pass (or +overload), are controlled by an oil pressure of about 20 pounds per +square inch, acting upon a piston of suitable size. In view of the fact +that a turbine by-pass valve opens only when the unit is required to +develop overload, or the vacuum fails, a good feature of this governing +mechanism is that the valve referred to can be kept constantly in +motion, thereby preventing sticking in an emergency, even though it be +actually called into action only at long intervals. Another feature of +importance is that the oil supply to the bearings, as well as that to +the governor, can be interconnected so that the governor will +automatically shut off the steam if the oil supply fails and endangers +the bearings. This mechanism is also so proportioned that, while +responding quickly to variations in load, its sensitiveness is kept +within such bounds as to secure the best results in the parallel +operation of alternators. The governor can be adjusted for speed while +the turbine is in operation, thereby facilitating the synchronizing of +alternators and dividing the load as may be desired. + +In order to provide for any possible accidental derangement of the main +governing mechanism, an entirely separate safety or over-speed governor +is furnished. This governor is driven directly by the turbine shaft +without the intervention of gearing, and is so arranged and adjusted +that, if the turbine should reach a predetermined speed above that for +which the main governor is set, the safety governor will come into +action and trip a valve which entirely shuts off the steam supply, +bringing the turbine to a stop. + + +Lubrication + +Lubrication of the four bearings, which are of the self-adjusting, ball +and socket pattern, is effected by supplying an abundance of oil to the +middle of each bearing and allowing it to flow out at the ends. The oil +is passed through a tubular cooler, having water circulation, and pumped +back to the bearings. Fig. 33 shows the entire arrangement graphically +and much more clearly than can be explained in words. The oil is +circulated by a pump directly operated from the turbine, except where +the power-house is provided with a central oiling system. Particular +stress is laid by the builders upon the fact that it is not necessary to +supply the bearings with oil under pressure, but only at a head +sufficient to enable it to run to and through the bearings; this head +never exceeding a few feet. With each turbine is installed a separate +direct-acting steam pump for circulating oil for starting up. This will +be referred to again under the head of operating. + +[Illustration: FIG. 33] + + +Generator + +The turbo-generator, which constitutes the electrical end of this unit, +is totally enclosed to provide for noiseless operation, and forced +ventilation is secured by means of a small fan carried by the shaft on +each end of the rotor. The air is taken in at the ends of the generator, +passes through the fans and is discharged over the end connections of +the armature coils into the bottom of the machine, whence it passes +through the ventilating ducts of the core to an opening at the top. The +field core is, according to size, built up either of steel disks, each +in one piece, or of steel forgings, so as to give high magnetic +permeability and great strength. The coils are placed in radial slots, +thereby avoiding side pressure on the slot insulation and the complex +stresses resulting from centrifugal force, which, in these rotors, acts +normal to the flat surface of the strip windings. + + +Operation + +As practically no adjustments are necessary when these units are in +operation, the greater part of the attention required by them is +involved in starting up and shutting down, which may be described in +detail as follows: + + +_To Start Up_ + +First, the auxiliary oil pump is set going, and this is speeded up until +the oil pressure shows a hight sufficient to lift the inlet valve and +oil is flowing steadily at the vents on all bearings. The oil pressure +then shows about 20 to 25 pounds on the "Relay Oil" gage, and 2 to 4 +pounds on the "Bearing Oil" gage. Next the throttle is opened, without +admitting sufficient steam to the turbine to cause the spindle to turn, +and it is seen that the steam exhausts freely into the atmosphere, also +that the high-pressure end of the turbine expands freely in its guides. +Water having been allowed to blow out through the steam-chest drains, +the drains are closed and steam is permitted to continue flowing through +the turbine not less than a half an hour (unless the turbine is warm to +start with, when this period may be reduced) still without turning the +spindle. After this it is advisable to shut off steam and let the +turbine stand ten minutes, so as to warm thoroughly, during which time +the governor parts may be oiled and any air which may have accumulated +in the oil cylinder above the inlet valve blown off. Then the throttle +should be opened sufficiently to start the turbine spindle to revolving +very slowly and the machine allowed to run in this way for five +minutes. + +Successive operations may be mentioned briefly as admitting water to the +oil cooler; bringing the turbine up to speed, at the same time slowing +down the auxiliary oil pump and watching that the oil pressures are kept +up by the rotary oil pump on the turbine; turning the water on to the +glands very gradually and, before putting on vacuum, making sure that +there is just enough water to seal these glands properly; and starting +the vacuum gradually just before putting on the load. These conditions +having been complied with, the operator next turns his attention to the +generator, putting on the field current, synchronizing carefully and +building up the load on the unit gradually. + +The principal precautions to be observed are not to start without +warming up properly, to make sure that oil is flowing freely through the +bearings, that vacuum is not put on until the water glands seal, and to +avoid running on vacuum without load on the turbine. + + +In Operation + +In operation all that is necessary is to watch the steam pressure at the +"Throttle" and "Inlet" gages, to see that neither this pressure nor the +steam temperature varies much; to keep the vacuum constant, as well as +pressures on the water glands and those indicated by the "Relay Oil" and +"Bearing Oil" gages; to take care that the temperatures of the oil +flowing to and from the bearings does not exceed 135 degrees Fahr. (at +which temperature the hand can comfortably grasp the copper oil-return +pipes); to see that oil flows freely at all vents on the bearings, and +that the governor parts are periodically oiled. So far as the generator +is concerned, it is only essential to follow the practice common in all +electric power plant operation, which need not be reviewed here. + +_Stopping the turbine_ is practically the reverse of starting, the +successive steps being as follows: starting the auxiliary oil pump, +freeing it of water and allowing it to run slowly; removing the load +gradually; breaking the vacuum when the load is almost zero, shutting +off the condenser injection and taking care that the steam exhausts +freely into the atmosphere; shutting off the gland water when the load +and vacuum are off; pulling the automatic stop to trip the valve and +shut off steam and, as the speed of the turbine decreases, speeding up +the auxiliary oil pump to maintain pressure on the bearings; then, when +the turbine has stopped, shutting down the auxiliary oil pump, turning +off the cooling water, opening the steam chest drains and slightly +oiling the oil inlet valve-stem. During these operations the chief +particulars to be heeded are: not to shut off the steam before starting +the auxiliary oil pump nor before the vacuum is broken, and not to shut +off the gland water with vacuum on the turbine. The automatic stop +should also remain unhooked until the turbine is about to be started up +again. + + +General + +Water used in the glands of the turbine must be free from scale-forming +impurities and should be delivered at the turbine under a steady +pressure of not less than 15 pounds. The pressure in the glands will +vary from 4 to 10 pounds. This water may be warm. In the use of water +for the cooling coils and of oil for the lubricating system, nothing +more is required than ordinary good sense dictates. An absolutely pure +mineral oil must be supplied, of a non-foaming character, and it should +be kept free through filtering from any impurities. + +The above refers particularly to Allis-Chalmers turbines of the type +ordinarily used for power service. For turbines built to be run +non-condensing, the part relating to vacuum does not, of course, apply. + + + + +IV. WESTINGHOUSE-PARSONS STEAM TURBINE + + +While the steam turbine is simple in design and construction and does +not require constant tinkering and adjustment of valve gears or taking +up of wear in the running parts, it is like any other piece of fine +machinery in that it should receive intelligent and careful attention +from the operator by inspection of the working parts that are not at all +times in plain view. Any piece of machinery, no matter how simple and +durable, if neglected or abused will in time come to grief, and the +higher the class of the machine the more is this true. + +Any engineer who is capable of running and intelligently taking care of +a reciprocating engine can run and take care of a turbine, but if he is +to be anything more than a starter and stopper, it is necessary that he +should know what is inside of the casing, what must be done and avoided +to prevent derangement, and to keep the machine in continued and +efficient operation. + +In the steam turbine the steam instead of being expanded against a +piston is made to expand against and to get up velocity in itself. The +jet of steam is then made to impinge against vanes or to react against +the moving orifice from which it issues, in either of which cases its +velocity and energy are more or less completely abstracted and +appropriated by the revolving member. The Parsons turbine utilizes a +combination of these two methods. + +[Illustration: FIG. 34] + +Fig. 34 is a sectional view of the standard Westinghouse-Parsons +single-flow turbine. A photograph of the rotor R R R is reproduced in +Fig. 35, while in Fig. 36 a section of the blading is shown upon a +larger scale. Between the rows of the blading upon the rotor extend +similar rows of stationary blades attached to the casing or stator. The +steam entering at A (Fig. 34), fills the circular space surrounding the +rotor and passes first through a row of stationary blades, 1 (Fig. 37), +expanding from the initial pressure P to the slightly lower pressure +P{1}, and attaining by that expansion a velocity with which it is +directed upon the moving blade 2. In passing through this row of blades +it is further expanded from pressure P{1} to P{2} and helps to push the +moving blades along by the reaction of the force with which it issues +therefrom. Impinging upon the second row of stationary blades 3, the +direction of flow is diverted so as to make it impinge at a favorable +angle upon the second row of revolving blades 4, and the action is +continued until the steam is expanded to the pressure of the condenser +or of the medium into which the turbine finally exhausts. As the +expansion proceeds, the passages are made larger by increasing the +length of the blades and the diameter of the drums upon which they are +carried in order to accommodate the increasing volume. + +[Illustration: FIG. 35] + +[Illustration: FIG. 36] + +[Illustration: FIG. 37] + +It is not necessary that the blades shall run close together, and the +axial clearance, that is the space lengthwise of the turbine between the +revolving and the stationary blades, varies from 1/8 to 1/2 inch; but in +order that there may not be excessive leakage over the tops of the +blades, as shown, very much exaggerated, in Fig. 38, the radial +clearance, that is, the clearance between the tops of the moving blades +and the casing, and between the ends of the stationary blades and the +shell of the rotor, must be kept down to the lowest practical amount, +and varies, according to the size of the machine and length of blade, +from about 0.025 to 0.125 of an inch. + +[Illustration: FIG. 38] + +In the passage A (Fig. 34) exists the initial pressure; in the passage B +the pressure after the steam has passed the first section or diameter of +the rotor; in the passage C after it has passed the second section. The +pressure acting upon the exposed faces of the rows of vanes would crowd +the rotor to the left. They are therefore balanced by pistons or +"dummies" P P P revolving with the shaft and exposing in the annular +spaces B^1 and C^1 the same areas as those of the blade sections which +they are designed to balance. The same pressure is maintained in B^1 as +in B, and in C^1 as in C by connecting them with equalizing pipes E E. +The third equalizing pipe connects the back or right-hand side of the +largest dummy with the exhaust passage so that the same pressure exists +upon it as exists upon the exhaust end of the rotor. These dummy pistons +are shown at the near end of the rotor in Fig. 35. They are grooved so +as to form a labyrinth packing, the face of the casing against which +they run being grooved and brass strips inserted, as shown in Fig. 39. +The dummy pistons prevent leakage from A, B^1 and C^1 to the condenser, +and must, of course, run as closely as practicable to the rings in the +casing, the actual clearance being from about 0.005 to 0.015 of an inch, +again depending on the size of the machine. + +[Illustration: FIG. 39] + +The axial adjustment is controlled by the device shown at T in Fig. 34 +and on a larger scale in Fig. 40. The thrust bearing consists of two +parts, T{1} T{2}. Each consists of a cast-iron body in which are placed +brass collars. These collars fit into grooves C, turned in the shaft as +shown. The halves of the block are brought into position by means of +screws S{1} S{2} acting on levers L{1} L{2} and mounted in the bearing +pedestal and cover. The screws are provided with graduated heads which +permit the respective halves of the thrust bearing to be set within one +one-thousandth of an inch. + +[Illustration: FIG. 40] + +The upper screw S{2} is set so that when the rotor exerts a light +pressure against it through the thrust block and lever the grooves in +the balance pistons are just unable to come in contact with the dummy +strips in the cylinder. The lower screw S{1} is then adjusted to permit +about 0.008 to 0.010 of an inch freedom for the collar between the +grooves of the thrust bearing. + +These bearings are carefully adjusted before the machine leaves the +shop, and to prevent either accidental or unauthorized changes of their +adjustment the adjusting screw heads are locked by the method shown in +Fig. 40. The screw cannot be revolved without sliding back the latch +L{3}. To do this the pin P{4} must be withdrawn, for which purpose the +bearing cover must be removed. + +In general this adjustment should not be changed except when there has +been some wear of the collars in the thrust bearing; nevertheless, it is +a wise precaution to go over the adjustment at intervals. The method of +doing this is as follows: The machine should have been in operation for +some time so as to be well and evenly heated and should be run at a +reduced speed, say 10 per cent. of the normal, during the actual +operation of making the adjustment. Adjust the upper screw which, if +tightened, would push the spindle away from the thrust bearing toward +the exhaust. Find a position for this so that when the other screw is +tightened the balance pistons can just be heard to touch, and so the +least change of position inward of the upper screw will cause the +contact to cease. To hear if the balance pistons are touching, a short +piece of hardwood should be placed against the cylinder casing near the +balance piston. If the ear is applied to the other end of the piece of +wood the contact of the balance pistons can be very easily detected. The +lower screw should then be loosened and the upper screw advanced from +five to fifteen one-thousandths, according to the machine, at which +position the latter may be considered to be set. The lower screw should +then be advanced until the under half of the thrust bearing pushes the +rotor against the other half of the thrust bearing, and from this +position it should be pushed back ten or more one-thousandths, to give +freedom for the rotor between the thrusts, and locked. A certain amount +of care should be exercised in setting the dummies, to avoid straining +the parts and thus obtain a false setting. + +The object in view is to have the grooves of the balance pistons running +as close as possible to the collars in the cylinder, but without danger +of their coming in actual contact, and to allow as little freedom as +possible in the thrust bearing itself, but enough to be sure that it +will not heat. The turbine rotor itself has scarcely any end thrust, so +that all the thrust bearing has to do is to maintain the +above-prescribed adjustment. + +The blades are so gaged that at all loads the rotor has a very light but +positive thrust toward the running face of the dummy strips, thus +maintaining the proper clearance at the dummies as determined by the +setting of the proper screw adjustment. + + +Main Bearings + +The bearings which support the rotor are shown at F F in Fig. 34 and in +detail in Fig. 41. The bearing proper consists of a brass tube B with +proper oil grooves. It has a dowel arm L which fits into a corresponding +recess in the bearing cover and which prevents the bearing from turning. +On this tube are three concentric tubes, C D E, each fitting over the +other with some clearance so that the shaft is free to move slightly in +any direction. These tubes are held in place by the nut F, and this nut, +in turn, is held by the small set-screw G. The bearing with the +surrounding tubes is placed inside of the cast-iron shell A, which rests +in the bearing pedestal on the block and liner H. The packing ring M +prevents the leakage of oil past the bearing. Oil enters the chamber at +one end of the bearing at the top and passes through the oil grooves, +lubricating the journal, and then out into the reservoir under the +bearing. The oil also fills the clearance between the tubes and forms a +cushion, which dampens any tendency to vibration. + +[Illustration: FIG. 41] + +The bearings, being supported by the blocks or "pads" H, are +self-alining. Under these pads are liners 5, 10, 20, and 50 thousandths +in thickness. By means of these liners the rotor may be set in its +proper running position relative to the stator. This operation is quite +simple. Remove the liners from under one bearing pad and place them +under the opposite pad until a blade touch is obtained by turning the +rotor over by hand. After a touch has been obtained on the top, bottom, +and both sides, the total radial blade clearance will be known to equal +the thickness of the liners transferred. The position of the rotor is +then so adjusted that the radial blade clearance is equalized when the +turbine is at operating temperature. + +On turbines running at 1800 revolutions per minute or under, a split +babbitted bearing is used, as shown in Figs. 42a and 42b. These bearings +are self-alining and have the same liner adjustment as the +concentric-sleeve bearings just described. Oil is supplied through a +hole D in the lower liner pad, and is carried to the oil groove F +through the tubes E E. The oil flows from the middle of this bearing to +both ends instead of from one end to the other, as in the other type. + +[Illustration: FIG. 42A] + +[Illustration: FIG. 42B] + + +Packing Glands + +Where the shaft passes through the casing at either end it issues from a +chamber in which there exists a vacuum. It is necessary to pack the +shaft at these points, therefore, against the atmospheric pressure, and +this is done by means of a water-gland packing W W (Fig. 34). Upon the +shaft in Fig. 35, just in front of the dummy pistons, will be seen a +runner of this packing gland, which runner is shown upon a larger scale +and from a different direction in Fig. 43. To get into the casing the +air would have to enter the guard at A (Fig. 44), pass over the +projecting rings B, the function of which is to throw off any water +which may be creeping along the shaft by centrifugal force into the +surrounding space C, whence it escapes by the drip pipe D, hence over +the five rings of the labyrinth packing E and thence over the top of the +revolving blade wheel, it being apparent from Fig. 43 that there is no +way for the air to pass by without going up over the top of the blades; +but water is admitted to the centrally grooved space through the pipe +shown, and is revolved with the wheel at such velocity that the pressure +due to centrifugal force exceeds that of the atmosphere, so that it is +impossible for the air to force the water aside and leak in over the +tips of the blades, while the action of the runner in throwing the water +out would relieve the pressure at the shafts and avoid the tendency of +the water to leak outward through the labyrinth packing either into +the vacuum or the atmosphere. + +[Illustration: FIG. 43] + +[Illustration: FIG. 44] + +The water should come to the glands under a head of about 10 feet, or a +pressure of about 5 pounds, and be connected in such a way that this +pressure may be uninterruptedly maintained. Its temperature must be +lower than the temperature due to the vacuum within the turbine, or it +will evaporate readily and find its way into the turbine in the form of +steam. + +[Illustration: FIG. 45] + +In any case a small amount of the steaming water will pass by the gland +collars into the turbine, so that if the condensed steam is to be +returned to the boilers the water used in the glands must be of such +character that it may be safely used for feed water. But whether the +water so used is to be returned to the boilers or not it should never +contain an excessive amount of lime or solid matter, as a certain amount +of evaporation is continually going on in the glands which will result +in the deposit of scale and require frequent taking apart for cleaning. + +[Illustration: FIG. 46] + +When there is an ample supply of good, clean water the glands may be +packed as in Fig. 45, the standpipe supplying the necessary head and the +supply valve being opened sufficiently to maintain a small stream at the +overflow. When water is expensive and the overflow must be avoided, a +small float may be used as in Fig. 46, the ordinary tank used by +plumbers for closets, etc., serving the purpose admirably. + +When the same water that is supplied to the glands is used for the +oil-cooling coils, which will be described in detail later, the coils +may be attached to either of the above arrangements as shown in Fig. 47. + +[Illustration: FIG. 47] + +When the only available supply of pure water is that for the boiler +feed, and the condensed steam is pumped directly back to the boiler, as +shown in Fig. 48, the delivery from the condensed-water pumps may be +carried to an elevation 10 feet above the axis of the glands, where a +tank should be provided of sufficient capacity that the water may have +time to cool considerably before being used. In most of these cases, if +so desired, the oil-cooling water may come from the circulating pumps of +the condenser, provided there is sufficient pressure to produce +circulation, as is also shown in Fig. 48. + +[Illustration: FIG. 48] + +When the turbine is required to exhaust against a back pressure of one +or two pounds a slightly different arrangement of piping must be made. +The water in this case must be allowed to circulate through the glands +in order to keep the temperature below 212 degrees Fahrenheit. If this +is not done the water in the glands will absorb heat from the main +castings of the machine and will evaporate. This evaporation will make +the glands appear as though they were leaking badly. In reality it is +nothing more than the water in the glands boiling, but it is +nevertheless equally objectionable. This may be overcome by the +arrangement shown in Fig. 49, where two connections and valves are +furnished at M and N, which drain away to any suitable tank or sewer. +These valves are open just enough to keep sufficient circulation so that +there is no evaporation going on, which is evidenced by steam coming out +as though the glands were leaking. These circulating valves may be used +with any of the arrangements above described. + +[Illustration: FIG. 49] + + +The Governor + +On the right-hand end of the main shaft in Fig. 34 there will be seen a +worm gear driving the governor. This is shown on a larger scale at A +(Fig. 50). At the left of the worm gear is a bevel gear driving the +spindle D of the governor, and at the right an eccentric which gives a +vibratory motion to the lever F. The crank C upon the end of the shaft +operates the oil pump. The speed of the turbine is controlled by +admitting the steam in puffs of greater or less duration according to +the load. The lever F, having its fulcrum in the collar surrounding the +shaft, operates with each vibration of the eccentric the pilot valve. +The valve is explained in detail later. + +[Illustration: FIG. 50] + +This form of governor has been superseded by an improved type, but so +many have been made that it will be well to describe its construction +and adjustment. The two balls W W (Fig. 50) are mounted on the ends of +bell cranks N, which rest on knife edges. The other end of the bell +cranks carry rollers upon which rest a plate P, which serves as a +support for the governor spring S. They are also attached by links to a +yoke and sleeve E which acts as a fulcrum for the lever F. The governor +is regulated by means of the spring S resting on the plate P and +compressed by a large nut G on the upper end of the governor spindle, +which nut turns on a threaded quill J, held in place by the nut H on the +end of the governor spindle and is held tight by the lock-nut K. To +change the compression of the spring and thereby the speed of the +turbine the lock-nut must first be loosened and the hand-nut raised to +lower the speed or lowered to raise the speed as the case may be. This +operation may be accomplished while the machine is either running or at +rest. + +The plate P rests upon ball bearings so that by simply bringing pressure +to bear upon the hand-wheel, which is a part of the quill J, the spring +and lock-nut may be held at rest and adjusted while the rest of the +turbine remains unaffected. Another lever is mounted upon the yoke E on +the pin shown at I, the other end of which is fastened to the piston of +a dash-pot so as to dampen the governor against vibration. Under the +yoke E will be noticed a small trigger M which is used to hold the +governor in the full-load position when the turbine is at rest. + +The throwing out of the weights elevates the sleeve E, carrying with it +the collar C, which is spanned by the lever F upon the shaft H. The +later turbines are provided with an improved form of governor operating +on the same principle, but embodying several important features. First, +the spindle sleeve is integral with the governor yoke, and the whole +rotates about a vertical stationary spindle, so that two motions are +encountered--a rotary motion and an up and down motion, according to the +position taken by the governor. This spiral motion almost entirely +eliminates the effect of friction of rest, and thereby enhances the +sensitiveness of the governor. Second, the governor weights move outward +on a parallel motion opposed directly by spring thrust, thus relieving +the fulcrum entirely of spring thrust. Third, the lay shaft driving the +governor oil pump and reciprocator is located underneath the main +turbine shaft, so that the rotor may be readily removed without in the +least disturbing the governor adjustment. + + +The Valve-Gear + +The valve-gear is shown in section in Fig. 51, the main admission being +shown at V{1} at the right, and the secondary V{2} at the left of the +steam inlet. The pilot valve F receives a constant reciprocating motion +from the eccentric upon the layshaft of the turbine through the lever F +(Fig. 50). These reciprocations run from 150 to 180 per minute. The +space beneath the piston C is in communication with the large steam +chest, where exists the initial pressure through the port A; the +admission of steam to the piston C being controlled by a needle valve +B. The pilot valve connects the port E, leading from the space beneath +the piston to an exhaust port I. + +[Illustration: FIG. 51] + +When the pilot valve is closed, the pressures can accumulate beneath the +piston C and raise the main admission valve from its seat. When the +pilot valve opens, the pressure beneath the piston is relieved and it is +seated by the helical spring above. If the fulcrum E (Fig. 50) of the +lever F were fixed the admission would be of an equal and fixed +duration. But if the governor raises the fulcrum E, the pilot valve F +(Fig. 51) will be lowered, changing the relations of the openings with +the working edges of the ports. + +The seating of the main admission valve is cushioned by the dashpot, the +piston of which is shown in section at G (Fig. 51). The valve may be +opened by hand by means of the lever K, to see if it is perfectly free. + +The secondary valve is somewhat different in its action. Steam is +admitted to both sides of its actuating piston through the needle valves +M M, and the chamber from which this steam is taken is connected with +the under side of the main admission valve, so that no steam can reach +the actuating piston of the secondary valve until it has passed through +the primary valve. When the pilot valve is closed, the pressures +equalize above and below the piston N and the valve remains upon its +seat. When the load upon the turbine exceeds its rated capacity, the +pilot valve moves upward so as to connect the space above the piston +with the exhaust L, relieving the pressure upon the upper side and +allowing the greater pressure below to force the valve open, which +admits steam to the secondary stage of the turbine. + +It would do no good to admit more steam to the first stage, for at the +rated capacity that stage is taking all the steam for which the blade +area will afford a passage. The port connecting the upper side of the +piston N with the exhaust may be permanently closed by means of the hand +valve Q, to be found on the side of the secondary pilot valve chest, +thus cutting the secondary valve entirely out of action. No dashpot is +necessary on this valve, the compression of the steam in the chamber W +by the fall of the piston being sufficient to avoid shock. + +The timing of the secondary valve is adjusted by raising or lowering the +pilot valve by means of the adjustment provided. It should open soon +enough so that there will not be an appreciable drop in speed before the +valve comes into play. The economy of the machine will be impaired if +the valve is allowed to open too soon. + + +Safety Stop Governor + +This device is mounted on the governor end of the turbine shaft, as +shown in Figs. 52 and 53. When the speed reaches a predetermined limit, +the plunger A, having its center of gravity slightly displaced from the +center of rotation of the shaft, is thrown radially outward and strikes +the lever B. It will easily be understood that when the plunger starts +outward, the resistance of spring C is rapidly overcome, since the +centrifugal force increases as the square of the radius, or in this case +the eccentricity of the center of gravity relative to the center of +rotation. Hence, the lever is struck a sharp blow. This releases the +trip E on the outside of the governor casing, and so opens the steam +valve F, which releases steam from beneath the actuating piston of a +quick-closing throttle valve, located in the steam line. Thus, within a +period of usually less than one second, the steam is entirely shut off +from the turbine when the speed has exceeded 7 or 8 per cent of the +normal. + +[Illustration: FIG. 52] + +[Illustration: FIG. 53] + + +The Oiling System + +Mounted on the end of the bedplate is the oil pump, operated from the +main shaft of the turbine as previously stated. This may be of the +plunger type shown in Fig. 54, or upon the latest turbine, the rotary +type shown in Fig. 55. Around the bedplate are located the oil-cooling +coils, the oil strainer, the oil reservoir and the oil pipings to the +bearing. + +[Illustration: FIG. 54] + +The oil reservoir, cooler, and piping are all outside the machine and +easily accessible for cleaning. Usually a corrugated-steel floor plate +covers all this apparatus, so that it will not be unsightly and +accumulate dirt, particularly when the turbine is installed, so that all +this apparatus is below the floor level; i.e., when the top of the +bedplate comes flush with the floor line. In cases where the turbine is +set higher, a casing is usually built around this material so that it +can be easily removed, and forms a platform alongside the machine. + +[Illustration: FIG. 55] + +The oil cooler, shown in Fig. 56, is of the counter-current type, the +water entering at A and leaving at B, oil entering at C (opening not +shown) and leaving at D. The coils are of seamless drawn copper, and +attached to the cover by coupling the nut. The water manifold F is +divided into compartments by transverse ribs, each compartment +connecting the inlet of each coil with the outlet of the preceding coil, +thus placing all coils in series. These coils are removable in one piece +with the coverplate without disturbing the rest of the oil piping. + +[Illustration: FIG. 56] + + +Blading + +[Illustration: FIG. 57] + +The blades are drawn from a rod consisting of a steel core coated with +copper so intimately connected with the other metal that when the bar is +drawn to the section required for the blading, the exterior coating +drawn with the rest of the bar forms a covering of uniform thickness as +shown in Fig. 57. The bar after being drawn through the correct section +is cut into suitable lengths punched as at A (Fig. 58), near the top of +the blade, and has a groove shown at B (Fig. 59), near the root, stamped +in its concave face, while the blade is being cut to length and punched. +The blades are then set into grooves cut into the rotor drum or the +concave surface of the casing, and spacing or packing pieces C (Fig. 59) +placed between them. These spacing pieces are of soft iron and of the +form which is desired that the passage between the blades shall take. +The groove made upon the inner face of the blade is sufficiently near to +the root to be covered by this spacing piece. When the groove has been +filled the soft-iron pieces are calked or spread so as to hold the +blades firmly in place. A wire of comma section, as shown at A (Fig. +59), is then strung through the punches near the outer ends of the +blades and upset or turned over as shown at the right in Fig. 58. This +upsetting is done by a tool which shears the tail of the comma at the +proper width between the blades. The bent-down portion on either side +of the blade holds it rigidly in position and the portion retained +within the width of the blade would retain the blade in its radial +position should it become loosened or broken off at the root. This comma +lashing, as it is called, takes up a small proportion only of the blade +length or projection and makes a job which is surprisingly stiff and +rigid, and yet which yields in case of serious disturbance rather than +to maintain a contact which would result in its own fusing or the +destruction of some more important member. + +[Illustration: FIG. 58] + +[Illustration: FIG. 59] + + +Starting Up the Turbine + +When starting up the turbine for the first time, or after any extended +period of idleness, special care must be taken to see that everything is +in good condition and that all parts of the machine are clean and free +from injury. The oil piping should be thoroughly inspected and cleaned +out if there is any accumulation of dirt. The oil reservoirs must be +very carefully wiped out and minutely examined for the presence of any +grit. (Avoid using cotton waste for this, as a considerable quantity of +lint is almost sure to be left behind and this will clog up the oil +passages in the bearings and strainer.) + +The pilot valves should be removed from the barrel and wiped off, and +the barrels themselves cleaned out by pushing a soft cloth through them +with a piece of wood. In no case should any metal be used. + +If the turbine has been in a place where there was dirt or where there +has been much dust blowing around, the bearings should be removed from +the spindle and taken apart and thoroughly cleaned. With care this can +be done without removing the spindle from the cylinder, by taking off +the bearing covers and very carefully lifting the weight of the spindle +off the bearings, then sliding back the bearings. It is best to lift the +spindle by means of jacks and a rope sling, as, if a crane is used, +there is great danger of lifting the spindle too high and thereby +straining it or injuring the blades. After all the parts have been +carefully gone over and cleaned, the oil for the bearing lubrication +should be put into the reservoirs by pouring it into the governor gear +case G (Fig. 34). Enough oil should be put in so that when the governor, +gear case, and all the bearing-supply pipes are full, the supply to the +oil pump is well covered. + +Special care should be taken so that no grit gets into the oil when +pouring it into the machine. Considerable trouble may be saved in this +respect by pouring the oil through cloth. + +A very careful inspection of the steam piping is necessary before the +turbine is run. If possible it should be blown out by steam from the +boilers before it is finally connected to the turbine. Considerable +annoyance may result by neglecting this precaution, from particles of +scale, red lead, gasket, etc., out of the steam pipe, closing up the +passages of the guide blades. + +When starting up, always begin to revolve the spindle without vacuum +being on the turbine. After the spindle is turning slowly, bring the +vacuum up. The reason for this is, that when the turbine is standing +still, the glands do not pack and air in considerable quantity will rush +through the glands and down through the exhaust pipe. This sometimes has +the effect of unequal cooling. In case the turbine is used in +conjunction with its own separate condenser, the circulating pump may be +started up, then the turbine revolved, and afterward the air pump put in +operation; then, last, put the turbine up to speed. In cases, however, +where the turbine exhausts into the same condenser with other machinery +and the condenser is therefore already in operation, the valve between +the turbine and the condenser system should be kept closed until after +the turbine is revolved, the turbine in the meantime exhausting through +the relief valve to atmosphere. + +Care must always be taken to see that the turbine is properly warmed up +before being caused to revolve, but in cases where high superheat is +employed always revolve the turbine just as soon as it is moderately +hot, and before it has time to become exposed to superheat. + +In the case of highly superheated steam, it is not undesirable to +provide a connection in the steam line by means of which the turbine may +be started up with saturated steam and the superheat gradually applied +after the shaft has been permitted to revolve. + +For warming up, it is usual practice to set the governor on the trigger +(see Fig. 50) and open the throttle valve to allow the entrance of a +small amount of steam. + +It is always well to let the turbine operate at a reduced speed for a +time, until there is assurance that the condenser and auxiliaries are in +proper working order, that the oil pump is working properly, and that +there is no sticking in the governor or the valve gear. + +After the turbine is up to speed and on the governor, it is well to +count the speed by counting the strokes of the pump rod, as it is +possible that the adjustment of the governor may have become changed +while the machine has been idle. It is well at this time, while there is +no load on the turbine, to be sure that the governor controls the +machine with the throttle wide open. It might be that the main poppet +valve has sustained some injury not evident on inspection, or was +leaking badly. Should there be some such defect, steps should be taken +to regrind the valve to its seat at the first opportunity. + +On the larger machines an auxiliary oil pump is always furnished. This +should be used before starting up, so as to establish the oil +circulation before the turbine is revolved. After the turbine has +reached speed, and the main oil pump is found to be working properly, it +should be possible to take this pump out of service, and start it again +only when the turbine is about to be shut down. + +If possible, the load should be thrown on gradually to obviate a sudden, +heavy demand upon the boiler, with its sometimes attendant priming and +rush of water into the steam pipe, which is very apt to take place if +the load is thrown on too suddenly. A slug of water will have the effect +of slowing down the turbine to a considerable extent, causing some +annoyance. There is not likely to be the danger of the damage that is +almost sure to occur in the reciprocating engine, but at the same time +it is well to avoid this as much as possible. A slug of water is +obviously more dangerous when superheated steam is being employed, owing +to the extreme temperature changes possible. + + +Running + +While the turbine is running, it should have a certain amount of careful +attention. This, of course, does not mean that the engineer must stand +over it every minute of the day, but he must frequently inspect such +parts as the lubricators, the oiling system, the water supply to the +glands and the oil-cooling coil, the pilot valve, etc. He must see that +the oil is up in the reservoir and showing in the gage glass provided +for that purpose, and that the oil is flowing freely through the +bearings, by opening the pet cocks in the top of the bearing covers. An +ample supply of oil should always be in the machine to keep the suction +in the tank covered. + +Care must be taken that the pump does not draw too much air. This can +usually be discovered by the bubbling up of the air in the governor +case, when more oil should be added. + +It is well to note from time to time the temperature of the bearings, +but no alarm need be occasioned because they feel warm to the touch; in +fact, a bearing is all right as long as the hand can be borne upon it +even momentarily. The oil coming from the bearings should be preferably +about 120 degrees Fahrenheit and never exceed 160 degrees. + +It should generally be seen that the oil-cooling coil is effective in +keeping the oil cool. Sometimes the cooling water deposits mud on the +cooling surface, as well as the oil depositing a vaseline-like +substance, which interferes with the cooling effect. The bearing may +become unduly heated because of this, when the coil should be taken out +at the first opportunity and cleaned on the outside and blown out by +steam on the inside, if this latter is possible. If this does not reduce +the temperature, either the oil has been in use too long without being +filtered, or the quality of the oil is not good. + +Should a bearing give trouble, the first symptom will be burning oil +which will smoke and give off dense white fumes which can be very +readily seen and smelled. However, trouble with the bearings is one of +the most unlikely things to be encountered, and, if it occurs, it is due +to some radical cause, such as the bearings being pinched by their caps, +or grit and foreign matter being allowed to get into the oil. + +If a bearing gets hot, be assured that there is some very radical cause +for it which should be immediately discovered and removed. Never, under +any circumstances, imagine that you can nurse a bearing, that has +heated, into good behavior. Turbine bearings are either all right or all +wrong. There are no halfway measures. + +The oil strainer should also be occasionally taken apart and thoroughly +cleaned, which operation may be performed, if necessary, while the +turbine is in operation. The screens should be cleaned by being removed +from their case and thoroughly blown out with steam. In the case of a +new machine, this may have to be done every two or three hours. In +course of time, this need only be repeated perhaps once a week. The +amount of dirt found will be an indication of the frequency with which +this cleaning is necessary. + +The proper water pressure, about five pounds per square inch, must be +maintained at the glands. Any failure of this will mean that there is +some big leak in the piping, or that the water is not flowing properly. + +The pilot valve must be working freely, causing but little kick on the +governor, and should be lubricated from time to time with good oil. + +Should it become necessary, while operating, to shut down the condenser +and change over to non-condensing operation, particular care should be +observed that the change is not made too suddenly to non-condensing, as +all the low-pressure sections of the turbine must be raised to a much +higher temperature. While this may not cause an accident, it is well to +avoid the stresses which necessarily result from the sudden change of +temperature. The same reasons, of course, do not hold good in changing +from non-condensing to condensing. + + +Shutting Down + +When shutting down the turbine the load may be taken off before closing +the throttle; or, as in the case of a generator operating on an +independent load, the throttle may be closed first, allowing the load to +act as a brake, bringing the turbine to rest quickly. In most cases, +however, the former method will have to be used, as the turbine +generally will have been operating in parallel with one or more other +generators. When this is the case, partially close the throttle just +before the load is to be thrown off, and if the turbine is to run +without load for some time, shut off the steam almost entirely in order +to prevent any chance of the turbine running away. There is no danger of +this unless the main valve has been damaged by the water when wet steam +has been used, or held open by some foreign substance, when, in either +case, there may be sufficient leakage to run the turbine above speed, +while running light. At the same time, danger is well guarded against by +the automatic stop valve, but it is always well to avoid a possible +danger. As soon as the throttle is shut, stop the condenser, or, in the +case where one condenser is used for two or more turbines, close the +valve between the turbine and the condenser. Also open the drains from +the steam strainer, etc. This will considerably reduce the time the +turbine requires to come to rest. Still more time may be saved by +leaving the field current on the generator. + +Care should be taken, when the vacuum falls and the turbine slows down, +to see that the water is shut off from the glands for fear it may leak +out to such an extent as to let the water into the bearings and impair +the lubricating qualities of the oil. + + +Inspection + +At regular intervals thorough inspection should be made of all parts of +the turbine. As often as it appears necessary from the temperature of +the oil, depending on the quality of the oil and the use of the turbine, +remove the oil-cooling coil and clean it both on the inside and outside +as previously directed; also clean out the chamber in which it is kept. +Put in a fresh supply of oil. This need not necessarily be new, but may +be oil that has been in use before but has been filtered. We recommend +that an oil filter be kept for this purpose. Entirely new oil need only +be put into the turbine when the old oil shows marked deterioration. +With a first-class oil this will probably be a very infrequent +necessity, as some new oil has to be put in from time to time to make up +the losses from leakage and waste. + +Clean out the oil strainer, blowing steam through the wire gauze to +remove any accumulation of dirt. Every six months to a year take off the +bearing covers, remove the bearings, and take them apart and clean out +thoroughly. Even the best oil will deposit more or less solid matter +upon hot surfaces in time, which will tend to prevent the free +circulation of the oil through the bearings and effectively stop the +cushioning effect on the bearings. Take apart the main and secondary +valves and clean thoroughly, seeing that all parts are in good working +order. Clean and inspect the governor and the valve-gear, wiping out any +accumulation of oil and dirt that may appear. Be sure to clean out the +drains from the glands so that any water that may pass out of them will +run off freely and will not get into the bearings. + +At the end of the first three months, and after that about once a year, +take off the cylinder cover and remove the spindle. When the turbine is +first started up, there is very apt to be considerable foreign matter +come over in the steam, such as balls of red lead or small pieces of +gasket too small to be stopped by the strainer. These get into the guide +blades in the cylinder and quite effectively stop them up. Therefore, +the blades should be gone over very carefully, and any such additional +accumulation removed. Examine the glands and equilibrium ports for any +dirt or broken parts. Particularly examine the glands for any deposit of +scale. All the scale should be chipped off the gland parts, as, besides +preventing the glands from properly packing, this accumulation will +cause mechanical contact and perhaps cause vibration of the machine due +to lack of freedom of the parts. The amount of scale found after the +first few inspections will be an indication of how frequently the +cleaning should be done. As is discussed later, any water that is +unsuitable for boiler feed should not be used in the glands. + +In reassembling the spindle and cover, very great care must be taken +that no blades are damaged and that nothing gets into the blades. Nearly +all the damage that has been done to blades has resulted from +carelessness in this respect; in fact, it is impossible to be too +careful. Particular care is also to be taken in assembling all the +parts and in handling them, as slight injury may cause serious trouble. +In no case should a damaged part be put back until the injury has been +repaired. + +If for any reason damaged blades cannot be repaired at the time, they +can be easily removed and the turbine run again without them until it is +convenient to put in new ones; in fact, machines have been run at full +load with only three-quarters of the total number of blades. In such an +event remove the corresponding stationary blades as well as the moving +blades, so as not to disturb the balance of the end thrust. + + +Conditions Conducive to Successful Operation + +In the operation of the turbine and the conditions of the steam, both +live and exhaust play a very important part. It has been found by +expensive experimenting that moisture in the steam has a very decided +effect on the economy of operation; or considerably more so than in the +case of the reciprocating engine. In the latter engine, 2 per cent. of +moisture will mean very close to 2 per cent. increase in the amount of +water supplied to the engine for a given power. On the other hand, in +the turbine 2 per cent. moisture will cause an addition of more nearly 4 +per cent. It is therefore readily seen that the drier the entering +steam, the better will be the appearance of the coal bill. + +By judicious use of first-class separators in connection with a suitable +draining system, such as the Holly system which returns the moisture +separated from the steam, back to the boilers, a high degree of quality +may be obtained at the turbine with practically no extra expense during +operation. Frequent attention should be given the separators and traps +to insure their proper operation. The quality of the steam may be +determined from time to time by the use of a throttling calorimeter. Dry +steam, to a great extent, depends upon the good and judicious design of +steam piping. + +Superheated steam is of great value where it can be produced +economically, as even a slight degree insures the benefits to be derived +from the use of dry steam. The higher superheats have been found to +increase the economy to a considerable extent. + +When superheat of a high degree (100 degrees Fahrenheit or above) is +used special care must be exercised to prevent a sudden rise of the +superheat of any amount. The greatest source of trouble in this respect +is when a sudden demand is made for a large increase in the amount of +steam used by the engine, as when the turbine is started up and the +superheater has been in operation for some time before, the full load is +suddenly thrown on. It will be readily seen that with the turbine +running light and the superheater operating, there is a very small +amount of steam passing through; in fact, practically none, and this may +become very highly heated in the superheater, but loses nearly all its +superheat in passing slowly to the turbine; then, when a sudden demand +is made, this very high temperature steam is drawn into the turbine. +This may usually be guarded against where a separately fired superheater +is used, by keeping the fire low until the load comes on, or, in the +case where the superheater is part of the boiler, by either not starting +up the superheater until after load comes on, or else keeping the +superheat down by mixing saturated steam with that which has been +superheated. After the plant has been started up there is little danger +from this source, but such precautions should be taken as seem best in +the particular cases. + +Taking up the exhaust end of the turbine, we have a much more striking +departure from the conditions familiar in the reciprocating engine. Due +to the limits imposed upon the volume of the cylinder of the engine, any +increase in the vacuum over 23 or 24 inches, in the case, for instance, +of a compound-condensing engine, has very little, if any, effect on the +economy of the engine. With the turbine, on the other hand, any increase +of vacuum, even up to the highest limits, increases the economy to a +very considerable extent and, moreover, the higher the vacuum the +greater will be the increase in the economy for a given addition to the +vacuum. Thus, raising the vacuum from 27 to 28 inches has a greater +effect than from 23 to 24 inches. For this reason the engineer will +readily perceive the great desirability of maintaining the vacuum at the +highest possible point consistent with the satisfactory and economical +operation of the condenser. + +The exhaust pipe should always be carried downward to the condenser when +possible, to keep the water from backing up from the condenser into the +turbine. If the condenser must be located above the turbine, then the +pipe should be carried first downward and then upward in the U form, in +the manner of the familiar "entrainer," which will be found effectively +to prevent water getting back when the turbine is operating. + + +Condensers + +As has been previously pointed out, the successful and satisfactory +operation of the turbine depends very largely on the condenser. With the +reciprocating engine, if the condenser will give 25 inches vacuum, it is +considered fairly good, and it is allowed to run along by itself until +the vacuum drops to somewhere below 20 inches, when it is completely +gone over, and in many cases practically rebuilt and the vacuum brought +back to the original 25 inches. It has been seen that this sort of +practice will never do in the case of the turbine condenser and, unless +the vacuum can be regularly maintained at 27 or 28 inches, the condenser +is not doing as well as it ought to do, or it is not of the proper type, +unless perhaps the temperature and the quantity of cooling water +available render a higher vacuum unattainable. + +On account of the great purity of the condensed steam from the turbine +and its peculiar availability for boiler feed (there being no oil of any +kind mixed with it to injure the boilers), the surface condenser is very +desirable in connection with the turbine. It further recommends itself +by reason of the high vacuum obtainable. + +Where a condenser system capable of the highest vacuum is installed, +the need of utilizing it to its utmost capacity can hardly be emphasized +too strongly. A high vacuum will, of course, mean special care and +attention, and continual vigilance for air leaks in the exhaust piping, +which will, however, be fully paid for by the great increase in economy. + +It must not be inferred that a high vacuum is essential to successful +operation of this type of turbine, for excellent performance both in the +matter of steam consumption and operation is obtained with inferior +vacuum. The choice of a condenser, however, is a matter of special +engineering, and is hardly within the province of this article. + + +Oils + +There are several oils on the market that are suitable for the purpose +of the turbine oiling system, but great care must be exercised in their +selection. In the first place, the oil must be pure mineral, +unadulterated with either animal or vegetable oils, and must have been +washed free from acid. Certain brands of oil require the use of +sulphuric acid in their manufacture and are very apt to contain varying +degrees of free acid in the finished product. A sample from one lot may +have almost no acid, while that from another lot may contain a dangerous +amount. + +Mineral oils that have been adulterated, when heated up, will partially +decompose, forming acid. These oils may be very good lubricants when +first put into use, but after awhile they lose all their good qualities +and become very harmful to the machine by eating the journals in which +they are used. These oils must be very carefully avoided in the turbine, +as the cheapness of their first cost will in no way pay for the damage +they may do. A very good and simple way to test for such adulterations +is to take up a quantity of the oil in a test tube with a solution of +borax and water. If there is any animal or vegetable adulterant present +it will appear as a white milk-like emulsion which will separate out +when allowed to stand. The pure mineral oil will appear at the top as a +clear liquid and the excess of the borax solution at the bottom, the +emulsion being in between. A number of oils also contains a considerable +amount of paraffin which is deposited in the oil-cooling coil, +preventing the oil from being cooled properly, and in the pipes and +bearings, choking the oil passages and preventing the proper circulation +of the oil and cushioning effect in the bearing tubes. This is not +entirely a prohibitive drawback, the chief objection being that it +necessitates quite frequently cleaning the cooling coil, and the oil +piping and bearings. + +Some high-class mineral oils of high viscosity are inclined to emulsify +with water, which emulsion appears as a jelly-like substance. It might +be added that high-grade oils having a high viscosity might not be the +most suitable for turbine use. + +Since the consumption of oil in a turbine is so very small, being +practically due only to leakage or spilling, the price paid for it +should therefore be of secondary importance, the prime consideration +being its suitability for the purpose. + +In some cases a central gravity system will be employed, instead of the +oil system furnished with the turbine, which, of course, will be a +special consideration. + +For large installations a central gravity oiling system has much to +recommend it, but as it performs such an important function in the power +plant, and its failure would be the cause of so much damage, every +detail in connection with it should be most carefully thought out, and +designed with a view that under no combination of circumstances would it +be possible for the system to become inoperative. One of the great +advantages of such a system is that it can be designed to contain very +large quantities of oil in the settling tanks; thus the oil will have +quite a long rest between the times of its being used in the turbine, +which seems to be very helpful in extending the life of the oil. Where +the oil can have a long rest for settling, an inferior grade of oil may +be used, providing, however, that it is absolutely free of acid. + + + + +V. PROPER METHOD OF TESTING A STEAM TURBINE[3] + +[3] Contributed to _Power_ by Thomas Franklin. + + +The condensing arrangements of a turbine are perhaps mainly instrumental +in determining the method of test. The condensed steam alone, issuing +from a turbine having, for example, a barometric or jet condenser, +cannot be directly measured or weighed, unless by meter, and these at +present are not sufficiently accurate to warrant their use for test +purposes, if anything more than approximate results are desired. The +steam consumed can, in such a case, only be arrived at by measuring the +amount of condensing water (which ultimately mingles with the condensed +steam), and subtracting this quantity from the condenser's total +outflow. Consequently, in the case of turbines equipped with barometric +or jet condensers, it is often thought sufficient to rely upon the +measurement taken of the boiler feed, and the boiler's initial and final +contents. Turbines equipped with surface-condensing plants offer better +facilities for accurate steam-consumption calculations than those plants +in which the condensed exhaust steam and the circulating water come into +actual contact, it being necessary with this type simply to pump the +condensed steam into a weighing or measuring tank. + +In the case of a single-flow turbine of the Parsons type, the covers +should be taken off and every row of blades carefully examined for +deposits, mechanical irregularities, deflection from the true radial and +vertical positions, etc. The blade clearances also should be gaged all +around the circumference, to insure this clearance being an average +working minimum. On no account should a test be proceeded with when any +doubt exists as to the clearance dimensions. + +[Illustration: FIG. 60] + +The dummy rings of a turbine, namely, those rings which prevent +excessive leakage past the balancing pistons at the high-pressure end, +should have especial attention before a test. A diagrammatic sketch of a +turbine cylinder and spindle is shown in Fig. 60, for the benefit of +those unfamiliar with the subject. In this A is the cylinder or casing, +B the spindle or rotor, and C the blades. The balancing pistons, D, E, +and F, the pressure upon which counterbalances the axial thrust upon the +three-bladed stages, are grooved, the brass dummy rings G G in the +cylinder being alined within a few thousandths of an inch of the grooved +walls, as indicated. After these rings have been turned (the turning +being done after the rings have been calked in the cylinder), it is +necessary to insure that each ring is perfectly bedded to its respective +grooved wall so that when running the several small clearances between +the groove walls and rings are equal. A capital method of thus bedding +the dummy rings is to grind them down with a flour of emery or +carborundum, while the turbine spindle is slowly revolving under steam. +Under these conditions the operation is performed under a high +temperature, and any slight permanent warp the rings may take is thus +accounted for. The turbine thrust-block, which maintains the spindle in +correct position relatively to the spindle, may also be ground with +advantage in a similar manner. + +The dummy rings are shown on a large scale in Fig. 61, and their +preliminary inspection may be made in the following manner: + +The spindle has been set and the dummy rings C are consequently within a +few thousandths of an inch of the walls _d_ of the spindle dummy grooves +D. The clearances allowed can be gaged by a feeler placed between a ring +and the groove wall. Before a test the spindle should be turned slowly +around, the feelers being kept in position. By this means any mechanical +flaws or irregularities in the groove walls may be detected. + +[Illustration: FIG. 61] + +It has sometimes been found that the groove walls, under the combined +action of superheated steam and friction, in cases where actual running +contact has occurred, have worn very considerably, the wear taking the +form of a rapid crumbling away. It is possible, however, that such +deterioration may be due solely to the quality of the steel from which +the spindle is forged. Good low-percentage carbon-annealed steel ought +to withstand considerable friction; at all events the wear under any +conditions should be uniform. If the surfaces of both rings and grooves +be found in bad condition, they should be re-ground, if not sufficiently +worn to warrant skimming up with a tool. + +As the question of dummy leakage is of very considerable importance +during a test, it may not be inadvisable to describe the manner of +setting the spindle and cylinder relatively to one another to insure +minimum leakage, and the methods of noting their conduct during a +prolonged run. In Fig. 62, showing the spindle, B is the thrust (made in +halves), the rings O of which fit into the grooved thrust-rings C in the +spindle. Two lugs D are cast on each half of the thrust-block. The +inside faces of these lugs are machined, and in them fit the ball ends +of the levers E, the latter being fulcrumed at F in the thrust-bearing +cover. The screws G, working in bushes, also fit into the thrust-bearing +cover, and are capable of pushing against the ends of the levers E and +thus adjusting the separate halves of the block in opposite directions. + +[Illustration: FIG. 62] + +The top half of the turbine cylinder having been lifted off, the spindle +is set relatively to the bottom half by means of the lower thrust-block +screw G. This screw is then locked in position and the top half of the +cover then lowered into place. With this method great care must +necessarily be exercised when lowering the top cover; otherwise the +brass dummy rings may be damaged. + +A safer method is to set the dummy rings in the center of the grooves of +the spindle, and then to lower the cover, with less possibility of +contact. There being usually plenty of side clearance between the blades +of a turbine, it may be deemed quite safe to lock the thrust-block in +its position, by screwing the screws G up lightly, and then to turn on +steam and begin running slowly. + +Next, the spindle may be very carefully and gradually worked in the +required direction, namely, in that direction which will tend to bring +the dummy rings and groove walls into contact, until actual but very +light contact takes place. The slightest noise made by the rubbing parts +inside the turbine can be detected by placing one end of a metal rod +onto the casing in vicinity of the dummy pistons, and letting the other +end press hard against the ear. Contact between the dummy rings and +spindle being thus demonstrated, the spindle must be moved back by the +screws, but only by the slightest amount possible. The merest fraction +of a turn is enough to break the contact, which is all that is required. +In performing this operation it is important, during the axial movements +of the spindle, to adjust the halves of the thrust-block so that there +can exist no possible play which would leave the spindle free to move +axially and probably vibrate badly. + +After ascertaining the condition of the dummy rings, attention might +next be turned to the thrust-block, which must not on any account be +tightened up too much. It is sufficient to say that the actual +requirements are such as will enable a very thin film of oil to +circulate between each wall of the spindle thrust-grooves and the brass +thrust-blocks ring. In other words, there should be no actual pressure, +irrespective of that exerted by the spindle when running, upon the +thrust-block rings, due to the separate halves having been nipped too +tightly. The results upon a test of considerable friction between the +spindle and thrust-rings are obvious. + +The considerations outlined regarding balancing pistons and dummy rings +can be dispensed with in connection with impulse turbines of the De +Laval and Rateau types, and also with double-flow turbines of a type +which does not possess any dummies. The same general considerations +respecting blade conditions and thrust-blocks are applicable, especially +to the latter type. With pure so-called impulse turbines, where the +blade clearances are comparatively large, the preliminary blade +inspection should be devoted to the mechanical condition of the blade +edges and passages. As the steam velocities of these types are usually +higher, the importance of minimizing the skin friction and eliminating +the possibility of eddies is great. + +Although steam leakage through the valves of a turbine may not +materially affect its steam consumption, unless it be the leakage +through the overload valve during a run on normal full load, a thorough +examination of all valves is advocated for many reasons. In a turbine +the main steam-inlet valve is usually operated automatically from the +governor; and whether it be of the pulsating type, admitting the steam +in blasts, or of the non-pulsating throttling type, it is equally +essential to obtain the least possible friction between all moving and +stationary parts. Similar remarks apply to the main governor, and any +sensitive transmitting mechanism connecting it with any of the turbine +valves. If a safety or "runaway" governor is possessed by the machine to +be tested, this should invariably be tried under the requisite +conditions before proceeding farther. The object of this governor being +automatically to shut off all steam from the turbine, should the latter +through any cause rise above the normal speed, it is often set to +operate at about 12 to 15 per cent. above the normal. Thus, a turbine +revolving at about 3000 revolutions per minute would be closed down at, +say, 3500, which would be within the limit of "safe" speed. + + +Importance of Oiling System and Water Service + +The oil question, being important, should be solved in the early stages +previously, if possible, to any official or unofficial consumption +tests. Whether the oil be supplied to the turbine bearings by a +self-contained system having the oil stored in the turbine bedplate or +by gravity from a separate oil source, does not affect the question in +its present aspect. The necessary points to investigate are four in +number, and may be headed as follows: + +(a) Examination of pipes and partitions for oil leakage. + +(b) Determination of volume of oil flowing through each bearing per unit +of time. + +(c) Examination for signs of water in oil. + +(d) Determination of temperature rise between inlet and outlet of oil +bearings. + +The turbine supplied with oil by the gravity or any other separate +system holds an advantage over the ordinary self-contained machine, +inasmuch as the oil pipes conveying oil into and from the bearings can +be easily approached and, if necessary, repaired. On the other hand, the +machine possessing its own oil tank, cooling chamber and pump is +somewhat at a disadvantage in this respect, as a part of the system is +necessarily hidden from view, and, further, it is not easily accessible. +The leakage taking place in any system, if there be any, must, however, +be detected and stopped. + +Fig. 63 is given to illustrate a danger peculiar to the self-contained +oil system, in which the oil and oil-cooling chambers are situated +adjacently in the turbine bedplate. One end of the bedplate only is +shown; B is a cast-iron partition dividing the oil chamber C from the +oil-cooling chamber D. Castings of this kind have sometimes a tendency +to sponginess and the trouble consequent upon this weakness would take +the form of leakage between the two chambers. Of course this is only a +special case, and the conditions named are hardly likely to exist in +every similarly designed plant. The capacity of oil, and especially of +hot oil, to percolate through the most minute pores is well known. +Consequently, in advocating extreme caution when dealing with oil +leakage, no apology is needed. + +[Illustration: FIG. 63] + +It may be stated without fear of contradiction that the oil in a +self-contained system, namely, a system in which the oil, stored in a +reservoir near or underneath the turbine, passes only through that one +turbine's bearings, and immediately back to the storage compartment, +deteriorates more rapidly than when circulating around an "entire" +system, such as the gravity or other analogous system. In the latter, +the oil tanks are usually placed a considerable distance from the +turbine or turbines, with the oil-cooling arrangements in fairly close +proximity. The total length of the oil circuit is thus considerably +increased, incidentally increasing the relative cooling capacity of the +whole plant, and thereby reducing the loss of oil by vaporization. + +The amount of oil passing through the bearings can be ascertained +accurately by measurement. With a system such as the gravity it is only +necessary to run the turbine up to speed, turn on the oil, and then, +over a period, calculate the volume of oil used by measuring the fall of +level in the storage tank and multiplying by its known cross-sectional +area. In those cases where the return oil, after passing through the +bearings, is delivered back into the same tank from which it is +extracted, it is of course necessary, during the period of test, to +divert this return into a separate temporary receptacle. Where the +system possesses two tanks, one delivery and one return (a superior +arrangement), this additional work is unnecessary. The same method can +be applied to individual turbines pumping their own oil from a tank in +the bedplate; the return oil, as previously described, being temporarily +prevented from running back to the supply. + +The causes of excessive oil consumption by bearings are many. There is +an economical mean velocity at which the oil must flow along the +revolving spindle; also an economical mean pressure, the latter +diminishing from the center of the bearing toward the ends. The aim of +the economist must therefore be in the direction of adjusting these +quantities correctly in relation to a minimum supply of oil per bearing; +and the principal factors capable of variation to attain certain +requirements are the several bearing clearances measured as annular +orifices, and the bearing diameters. + +It is not always an easy matter to detect the presence of water in an +oil system, and this difficulty is increased in large circuits, as the +water, when the oil is not flowing, generally filters to the lowest +members and pipes of the system, where it cannot usually be seen. A +considerable quantity of water in any system, however, indicates its +presence by small globular deposits on bearings and spindles, and in the +worst cases the water can clearly be seen in a small sample tapped from +the oil mains. There is only one effective method of ridding the oil of +this water, and this is by allowing the whole mass of oil in the system +to remain quiescent for a few days, after which the water, which falls +to the lowest parts, can be drained off. A simple method of clearing out +the system is to pump all the oil the whole circuit contains through the +filters, and thence to a tank from which all water can be taken off. One +of the ordinary supply tanks used in the gravity system will serve this +purpose, should a temporary tank not be at hand. If necessary, the +headers and auxiliary pipes of the system can be cleaned out before +circulating the oil again, but as this is rather a large undertaking, it +need only be resorted to in serious cases. + +[Illustration: FIG. 64] + +It is seldom possible to discover the correct and permanent temperature +rise of the circulating oil in a turbine within the limited time usually +alloted for a test. After a continuous run of one hundred hours it is +possible that the temperature at the bearing outlets may be lower than +it was after the machine had run for, say, only twenty hours. As a +matter of fact an oil-temperature curve plotted from periodical readings +taken over a continuous run of considerable length usually reaches a +maximum early, afterward falling to a temperature about which the +fluctuations are only slight during the remainder of the run. Fig. 64 +illustrates an oil-temperature curve plotted from readings taken over a +period of twenty-four hours. In this case the oil system was of the +gravity description, the capacity of the turbine being about 6000 +kilowatts. The bearings were of the ordinary white-metal spherical type. +Over extended runs of hundreds and even thousands of hours, the above +deductions may be scarcely applicable. Running without break for so +long, a small turbine circulating its own lubricant would possibly +require a renewal of the oil before the run was completed, in the main +owing to excessive temperature rise and consequent deterioration of the +quality of the oil. Under these conditions the probabilities are that +several temperature fluctuations might occur before the final maximum, +and more or less constant, temperature was reached. In this connection, +however, the results obtained are to a very large extent determined by +the general mechanical design and construction of the oiling system and +turbine. A reference to Fig. 63 again reveals at once a weakness in that +design, namely, the unnecessarily close proximity in which the oil and +water tanks are placed. + +[Illustration: FIG. 65] + +A design of thermometer cup suitable for oil thermometers is given in +Fig. 65 in which A is an end view of the turbine bedplate, B is a +turbine bearing and C and D are the inlet and outlet pipes, +respectively. The thermometer fittings, which are placed as near the +bearing as is practicable, are made in the form of an angular tee +fitting, the oil pipes being screwed into its ends. The construction of +the oil cup and tee piece is shown in the detail at the left where A is +the steel tee piece, into which is screwed the brass thermometer cup B. +The hollow bottom portion of this cup is less than 1/16 of an inch in +thickness. The top portion of the bored hole is enlarged as shown, and +into this, around the thermometer, is placed a non-conducting material. +The cup itself is generally filled with a thin oil of good conductance. + +Allied to the oil system of a turbine plant is the water service, of +comparatively little importance in connection with single self-contained +units of small capacity, where the entire service simply consists of a +few coils and pipes, but of the first consideration in large +installations having numerous separate units supplied by oil and water +from an exterior source. The largest turbine units are often supplied +with water for cooling the bearings and other parts liable to attain +high temperature. Although the water used for cooling the bearings +indirectly supplements the action taking place in the separate oil +coolers, it is of necessity a separate auxiliary service in itself, and +the complexity of the system is thus added to. A carefully constructed +water service, however, is hardly likely to give trouble of a mechanical +nature. The more serious deficiencies usually arise from conditions +inherent to the design, and as such must be approached. + + +Special Turbine Features to be Inquired into + +Before leaving the prime mover itself, and proceeding to the auxiliary +plant inspection, it may be well to instance a few special features +relating to the general conduct of a turbine, which it is the duty of a +tester to inquire into. There are certain specified qualifications which +a machine must hold when running under its commercial conditions, among +these being lack of vibration of both turbine and machinery driven, be +it generator or fan, the satisfactory running of auxiliary turbine parts +directly driven from the turbine spindle, minimum friction between the +driving mediums, such as worm-wheels, pumps, fans, etc., slight +irregularities of construction, often resulting in heated parts and +excessive friction and wear, and must therefore be detected and righted +before the final test. Furthermore, those features of design--and they +are not infrequent in many machines of recent development--which, in +practice, do not fulfil theoretical expectations, must be re-designed +upon lines of practical consistency. The experienced tester's opinion is +often at this point invaluable. To illustrate the foregoing, Figs. 66, +67, and 68 are given, representing, respectively, three distinct phases +in the evolution of a turbine part, namely, the coupling. Briefly, an +ordinary coupling connecting a driving and a driven shaft becomes +obstinate when the two separate spindles which it connects are not truly +alined. The desire of turbine manufacturers has consequently been to +design a flexible coupling, capable of accommodating a certain want of +alinement between the two spindles without in any way affecting the +smooth running of the whole unit. + +[Illustration: FIG. 66] + +[Illustration: FIG. 67] + +In Fig. 66 A is the turbine spindle end and B the generator spindle end, +which it is required to drive. It will be seen from the cross-sectional +end view that both spindle ends are squared, the coupling C, with a +square hole running through it, fitting accurately over both spindle +ends as shown. Obviously the fit between the coupling and spindle in +this case must be close, otherwise considerable wear would take place; +and equally obvious is the fact than any want of alinement between the +two spindles A and B will be accompanied by a severe strain upon the +coupling, and incidentally by many other troubles of operation of which +this inability of the coupling to accommodate itself to a little want +of alinement is the inherent cause. + +Looking at the coupling illustrated in Fig. 67, it will be seen that +something here is much better adapted to dealing with troubles of +alinement. The turbine and generator spindles A and B, respectively, are +coned at the ends, and upon these tapered portions are shrunk circular +heads C and D having teeth upon their outer circumferences. Made in +halves, and fitting over the heads, is a sleeve-piece, with teeth cut +into its inner bored face. The teeth of the heads and sleeve are +proportioned correctly to withstand, without strain, the greatest +pressure liable to be thrown upon them. There is practically no play +between the teeth, but there exists a small annular clearance between +the periphery of the heads and the inside bore of the sleeve, which +allows a slight lack of alinement to exist between the two spindles, +without any strain whatever being felt by the coupling sleeve E. The +nuts F and G prevent any lateral movement of the coupling heads C and D. +For all practical requirements this type of coupling is satisfactory, as +the clearances allowed between sliding sleeve and coupling heads can +always be made sufficient to accommodate a considerable want of +alinement, far beyond anything which is likely to occur in actual +practice. Perhaps the only feature against it is its lack of simplicity +of construction and corresponding costliness. + +[Illustration: FIG. 68] + +The type illustrated in Fig. 68 is a distinct advance upon either of the +two previous examples, because, theoretically at least, it is capable of +successfully accommodating almost any amount of spindle movement. The +turbine and generator spindle ends, A and B, have toothed heads C and D +shrunk upon them, the heads being secured by the nuts E and F. The +teeth in this case are cut in the enlarged ends as shown. A sleeve G, +made in halves, fits over the heads, and the teeth cut in each half +engage with those of their respective heads. All the teeth and teeth +faces are cut radially, and a little side play is allowed. + + +The Condenser + +To some extent, as previously remarked, the condenser and condensing +arrangements are instrumental in determining the lines upon which a test +ought to be carried out. In general, the local features of a plant +restrict the tester more or less in the application of his general +methods. A thorough inspection, including some preliminary tests if +necessary, is as essential to the good conduct of the condensing plant +as to the turbine above it. It may be interesting to outline the usual +course this inspection takes, and to draw attention to a few of the +special features of different plants. For this purpose a type of +vertical condenser is depicted in Fig. 69. Its general principle will be +gathered from the following description: + +Exhaust steam from the turbine flows down the pipe T and enters the +condenser at the top as shown, where it at once comes into contact with +the water tubes in W. These tubes fill an annular area, the central +un-tubed portion below the baffle cap B forming the vapor chamber. The +condensed steam falls upon the bottom tube-plate P and is carried away +by the pipe S leading to the water pump H. The Y pipe E terminating +above the level of the water in the condenser enters the dry-air pump +section pipe A. Cold circulating water enters the condenser at the +bottom, through the pipe I, and entering the water chamber X proceeds +upward through the tubes into the top-water chamber Y, and from there +out of the condenser through the exit pipe. It will be observed that the +vapor extracted through the plate P passes on its journey out of the +condenser through the cooling chamber D surrounded by the cold +circulating water. This, of course, is a very advantageous feature. At R +is the condenser relief, at U the relief valve for the water chambers. + +[Illustration: FIG. 69] + +A new condenser, especially if it embody new and untried features, +generally requires a little time and patience ere the best results can +be obtained from it. Perhaps the quickest and most satisfactory method +of getting at the weak points of this portion of a plant is to test the +various elements individually before applying a strict load test. Thus, +in dealing with a condenser similar to that illustrated in Fig. 69, the +careful tester would probably make, in addition to a thorough mechanical +examination, three or four individual vacuum and water tests. A brief +description of these will be given. The water test, the purpose of which +is to discover any leakage from the tubes, tube-plates, water pipes, +etc., into portions of the steam or air chambers, should be made first. + + +Water Tests of Condenser + +The condenser is first thoroughly dried out, particular care being given +to the outside of the tubes and the bottom tube-plate P. Water is then +circulated through the tubes and chambers for an hour or two, after +which the pumps are stopped, all water is allowed to drain out and a +careful examination is made inside. Any water leaking from the tubes +above the bottom baffle-plate will ultimately be deposited upon that +plate. It is essential to stop this leakage if there be any, otherwise +the condensed steam measured during the consumption test will be +increased to the extent of the leakage. A slight leakage in a large +condenser will obviously not affect the results to any serious extent. +The safest course to adopt when a leak is discovered and it is found +inopportune to effect immediate repair is to measure the actual volume +of leakage over a specified period, and the quantity then being known it +can be subtracted from the volume of the condensed steam at the end of +the consumption test. + +It is equally essential that no leakage shall occur between the bottom +tube-plate P and the tube ends. The soundness of the tube joints, and +the joint at the periphery of the tube-plate can be tested by well +covering the plate with water, the water chamber W and cooling chamber +having been previously emptied, and observing the under side of the +plate. It must be admitted that the practice of measuring the extent of +a water leak over a period, and afterward with this knowledge adjusting +the obtained quantities, is not always satisfactory. On no account +should any test be made with considerable water leakage inside the +condenser. The above method, however, is perhaps the most reliable to be +followed, if during its conduct the conditions of temperature in the +condenser are made as near to the normal test temperature as possible. +There are many condensers using salt water in their tubes, and in these +cases it would seem natural to turn to some analytical method of +detecting the amount of saline and foreign matter leaking into the +condensed steam. Unless, however, only approximate results are required, +such methods are not advocated. There are many reasons why they cannot +be relied upon for accurate results, among these being the variation in +the percentage of saline matter in the sea-water, the varying +temperature of the condenser tubes through which the water flows, and +the uncertainty of such analysis, especially where the percentage +leakage of pure saline matter is comparatively small. + + +The Vacuum Test + +Having convinced himself of the satisfactory conduct of the condenser +under the foregoing simple preparatory water tests, the tester may +safely pass to considerations of vacuum. There exists a good +old-fashioned method of discovering the points of leakage in a vacuum +chamber, namely, that of applying the flame of a candle to all seams and +other vulnerable spots, which in the location of big leaks is extremely +valuable. Assuming that the turbine joints and glands have been found +capable of preventing any inleak of air, with only a small absolute +pressure of steam or air inside it, and, further, an extremely important +condition, with the turbine casing at high and low temperatures, +separately, a vacuum test can be conducted on the condenser alone. + +This test consists of three operations. In the first place a high vacuum +is obtained by means of the air pump, upon the attainment of which +communication with everything else is closed, and results noted. The +second operation consists in repeating the above with the water +circulating through the condenser tubes, the results in this case also +being carefully tabulated. Before conducting the third test, the +condensers must be thoroughly warmed throughout, by running the turbine +for a short time if necessary, and after closing communication with +everything, allowing the vacuum to slowly fall. + +A careful consideration and comparison of the foregoing tests will +reveal the capabilities of the condenser in the aspect in which it is +being considered, and will suggest where necessary the desirable steps +to be taken. + + + + +VI. TESTING A STEAM TURBINE[4] + +[4] Contributed to _Power_ by Thomas Franklin. + + +Special Auxiliary Plant for Consumption Test + +There are one or two points of importance in the conduct of a test on a +turbine and these will be briefly touched upon. Fig. 70 illustrates the +general arrangement of the special auxiliary plant necessary for +carrying through a consumption test, when the turbine exhaust passes +through a surface condenser. The condensed steam, after leaving the +condenser, passes along the pipe A to the pump, and is then forced along +the pipe B (leading under ordinary circumstances to the hot-well), +through the main water valve C directly to the measuring tanks. To enter +these the water has to pass through the valves D and E, while the valves +F and G are for quickly emptying the tanks when necessary, being of a +larger bore than the inlet valves. The inlet pipes H I are placed +directly above the outlet valves, and thus, when required, before any +measurements are taken, the water can flow directly through the outlet +valves, the pipes terminating only a short distance above them, away to +an auxiliary tank or directly to the hot-well. Levers K and L fulcrumed +at J and J are connected to the valve spindles by auxiliary levers. The +valve arrangement is such that by pulling down the lever K the inlet +valve D is opened and the inlet valve E is closed. Again, by pulling +down the lever L the outlet valve F is closed, while the outlet valve G +is also simultaneously closed. + +[Illustration: FIG. 70] + +During a consumption test the valves are operated in the following +manner: The lever K is pulled down, which opens the inlet valve to the +first tank and closes that to the second. The bottom lever L, however, +is lifted, which for the time being opens the outlet valve F, and +incidentally opens the valve G; the latter valve can; however, for the +moment be neglected. When the turbine is started, and the condensed +steam begins to accumulate in the condenser, the water is pumped along +the pipes and, both the inlet and outlet valves on the first tank being +open, passes through, without any being deposited in the tank, to the +drain. This may be continued until all conditions are right for a +consumption test and, the time being carefully noted, lever L is quickly +pulled down and the valves F and G closed. The first tank now gradually +fills, and after a definite period, say fifteen minutes, the lever K is +pushed up, thus diverting the flow into the second tank. While the +latter is filling, the water in the first tank is measured, and the tank +emptied by a large sluice valve, not shown. + +The operation of alternately filling, measuring, and emptying the two +measuring tanks is thus carried on until the predetermined time of +duration of test has expired, when the total water as measured in the +tanks, and representing the amount of steam condensed during that time, +is easily found by adding together the quantities given at each +individual measurement. + +All that are necessary to insure successful results from a plant similar +to this are care and accuracy in its operation and construction. +Undoubtedly in most cases it is preferable to weigh the condensed steam +instead of measuring the volume passed, and from that to calculate the +weight. If dependence is being placed upon the volumetric method, it is +advisable to lengthen the duration of the test considerably, and if +possible to measure the feed-water evaporated at the same time. Such a +course, however, would necessitate little change, and none of a radical +nature, from the arrangement described. Where, however, the measuring +method is adopted, the all-important feature, requiring on the tester's +part careful personal investigation, is the graduation of the tanks. It +facilitates this operation very considerably when the receptacles are +graduated upon a weight scale. That is to say, whether or not a vertical +scale showing the actual hight of water be placed inside the tank, it is +advisable to have a separate scale indicating at once to the attendant +the actual contents, by weight, of the tank at any time. It is the +tester's duty to himself to check the graduation of this latter scale by +weighing the water with which he performs the operation of checking. + +Apart from the foregoing, there is little to be said about the measuring +apparatus. As has been stated, accuracy of result depends in this +connection, as in all others, upon careful supervision and sound and +accurate construction, and this the tester can only positively insure by +exhaustive inspection in the one case and careful deliberation in the +conduct of the other. + +It will be readily understood that the procedure--and this implies some +limitations--of a test is to an extent controlled by the conditions, or +particular environment of the moment. This is strictly true, and as a +consequence it is often impossible, in a maker's works, for example, to +obtain every condition, coinciding with those specified, which are to be +had on the site of final operation only. For this reason it would +appear best to reserve the final and crucial test of a machine, which +test usually in the operating sense restricts a prime mover in certain +directions with regard to its auxiliary plant, etc., until the machine +has been finally erected on its site. Obviously, unless a machine had +become more or less standardized, a preliminary consumption test would +be necessary, but once this primary qualification respecting consumption +had been satisfactorily settled, there appears to be no reason why +exhaustive tests in other directions should not all be carried out upon +the site, where the conditions for them are so much more favorable. + +When the steam consumption of a steam turbine is so much higher than the +guaranteed quantity, it usually takes little less than a reconstruction +to put things right. The minor qualifications of a machine, however, +which can be examined into and tested with greater ease, and usually at +considerably less expense, upon the site, and consequently under +specified conditions, may be advantageously left over until that site is +reached, where it is obvious that any shortcomings and general +deficiency in performance will be more quickly detected and diagnosed. + + +Test Loads from the Tester's View-point + +Before proceeding to describe the points of actual interest in the +consumption test, a few considerations respecting test loads will be +dealt with from the tester's point of view. Here again we often find +ourselves restricted, to an extent, by the surrounding conditions. The +very first considerations, when undertaking to carry out a consumption +test, should be devoted to obtaining the steadiest possible lead +[Transcriber: load?]. It may be, and is in many cases, that +circumstances are such as to allow a steady electrical load to be +obtained at almost any time. On the other hand an electrical load of any +description is sometimes not procurable at all, without the installation +of a special plant for the purpose. In such cases a mechanical friction +load, as, for example, that obtained by the water brake, is sometimes +available, or can easily be procured. Whereas, however, this type of +load may be satisfactory for small machines, it is usually quite +impossible for use with large units, of, say, 5000 kilowatts and upward. +It is seldom, however, that turbines are made in large sizes for +directly driving anything but electrical plants, although there is every +possibility of direct mechanical driving between large steam turbines +and plants of various descriptions, shortly coming into vogue, so that +usually there exist some facilities for obtaining an electrical load at +both the maker's works and upon the site of operation. + +One consideration of importance is worth inquiring into, and this has +relation to the largest turbo-generators supplied for power-station and +like purposes. Obviously, the testing of, say, a 7000-kilowatt +alternator by any standard electrical-testing method must entail +considerable expense, if such a test is to be carried out in the maker's +works. Nor would this expense be materially decreased by transferring +the operations to the power-station, and there erecting the necessary +electrical plant for obtaining a water load, or any other installation +of sufficient capacity to carry the required load according to the rated +full capacity of the machine. + +Assuming, then, that there exist no permanent facilities at either end, +namely the maker's works and the power station, for adequately procuring +a steady electrical-testing load of sufficient capacity, there still +remains, in this instance, an alternative source of power which is +usually sufficiently elastic to serve all purposes, and this is of +course the total variable load procurable from the station bus-bars. It +is conceivable that one out of a number of machines running in parallel +might carry a perfectly steady load, the latter being a fraction of a +total varying quantity, leaving the remaining machines to receive and +deal with all fluctuations which might occur. Even in the event of there +being only two machines, it is possible to maintain the load on one of +them comparatively steady, though the percentage variation in load on +either side of the normal would in the latter case be greater than in +the previous one. This is accomplished by governor regulation after the +machines have been paralleled. For example, assuming three +turbo-alternators of similar make and capacity to be running in +parallel, each machine carrying exactly one-third of the total +distributed load, it is fair to regard the governor condition, allowing +for slight mechanical disparities of construction, of all three machines +as being similar; and even in the case of three machines of different +capacity and construction, the governor conditions when the machines +are paralleled are more or less relatively and permanently fixed in +relation to one another. In other words, while the variation in load on +each machine is the same, the relative variation in the governor +condition must be constant. + +By a previously mentioned system of governor regulation, however, it is +possible, considering again for a moment the case of three machines in +parallel, by decreasing the sensitiveness of one governor only, to +accommodate nearly all the total variation in load by means of the two +remaining machines, the unresponsiveness of the one governor to change +in speed maintaining the load on that machine fairly constant. By this +method, at any rate, the variation in load on any one machine can be +minimized down to, say, 3 per cent, either side of the normal full load. + +There is another and more positive method by which a perfectly steady +load can be maintained upon one machine of several running in parallel. +This may be carried out as follows: Suppose, in a station having a total +capacity of 20,000 kilowatts, there are three machines, two of 6000 +kilowatts each, and one of 8000 kilowatts, and it is desired to carry +out a steady full-load test upon one of the 6000 kilowatts units. +Assuming that the test is to be of six hours' duration, and that the +conditions of load fluctuations upon the station are well known, the +first step to take is to select a period for the test during which the +total load upon all machines is not likely to fall below, say, 8000 +kilowatts. The tension upon the governor spring of the turbine to be +tested must then be adjusted so that the machine on each peak load is +taxed to its utmost normal capacity; and even when the station load +falls to its minimum, the load from the particular machine shall not be +released sufficiently to allow it to fall below 6000 kilowatts. Under +these conditions, then, it may be assumed that although the load on the +test machine will vary, it cannot fall below 6000 kilowatts. Therefore, +all that remains to be done to insure a perfectly steady load equal to +the normal full load of the machine, or 6000 kilowatts, is to fix the +main throttle or governing valve in such a position that the steam +passing through at constant pressure is just capable of sustaining full +speed under the load required. When this method is adopted, it is +desirable to fix a simple hight-adjusting and locking mechanism to the +governing-valve spindle. The load as read on the indicating wattmeter +can then be very accurately varied until correct, and farther varied, if +necessary, should any change occur in the general conditions which might +either directly or indirectly bring about a change of load. + + +Preparing the Turbine for Testing + +All preliminary labors connected with a test being satisfactorily +disposed of, it only remains to place the turbines under the required +conditions, and to then proceed with the test. For the benefit of those +inexperienced in the operation of large turbines, we will assume that +such a machine is about to be started for the purpose outlined. + +It is always advisable to make a strict practice of getting all the +auxiliary plant under way before starting up the turbine. In handling a +turbine plant the several operations might be carried through in the +following order: + +(1) Circulating oil through all bearings and oil chambers.[5] + +(2) Starting of condenser circulating-water pumps, and continuous +circulation of circulating water through the tubes of condenser. + +(3) Starting of pump delivering condensed steam from the condenser +hot-well to weighing tanks. + +(4) Starting of air pump, vacuum being raised as high as possible within +condenser. + +(5) Sealing of turbine glands, whether of liquid or steam type, no +adjustment of the quantity of sealing fluid being necessary, however, at +this point. + +(6) Adjustment of valves on and leading to the water-weighing tanks. + +(7) Opening of main exhaust valve or valves between turbine and +condenser. + +(8) Starting up of turbine and slowly running to speed. + +(9) Application of load, and adjustment of gland-sealing steam. + +[5] In a self-contained system, where the oil pump is usually driven +from the turbine spindle, this would of course be impossible. In the +gravity and allied systems, however, it should always be the first +operation performed. The tests for oil consumption, described +previously, having been carried out, it is assumed that suitable means +have been adopted to restrict the total oil flow through the bearings to +a minimum quantity. + +The running to speed of large turbo-alternators requires considerable +care, and should always be done slowly; that is to say the rate of +acceleration should be slow. It is well known that the vibration of a +heavy unit is accompanied by a synchronous or non-synchronous vibration +of the foundation upon which it rests. The nearest approach to perfect +synchronism between unit and foundation is obtained by a gradual rise in +speed. A machine run up to speed too quickly might, after passing the +critical speed, settle down with little visible vibration, but at a +later time, even hours after, suddenly begin vibrating violently from no +apparent cause. The chances of this occurring are minimized by slow and +careful running to speed. + +Whether the machine being tested is one of a number running in parallel, +or a single unit running on a steady water load, the latter should in +all cases be thrown on gradually until full load is reached. A +preliminary run of two or three hours--whenever possible--should then be +made, during which ample opportunity is afforded for regulating the +conditions in accordance with test requirements. The tester will do well +during the last hour of this trial run to station his recorders at their +several posts and, for a short time at least, to have a complete set of +readings taken at the correct test intervals. This more particularly +applies to the electrical water, superheat and vacuum readings. In the +case of a turbo-alternator the steadiness obtainable in the electrical +load may determine the frequency of readings taken, both electrical and +otherwise. On a perfectly steady water-tank load, for example, it may +be sufficiently adequate to read all wattmeters, voltmeters, and +ammeters from standard instruments at from one- to two-minute intervals. +Readings at half-minute intervals, however, should be taken with a +varying load, even when the variation is only slight. + +The water-measurement readings may of course be taken at any suitable +intervals, the time being to an extent determined by the size of the +measuring tanks or the capacity of the weighing machine or machines. +When designing the measuring apparatus, the object should be to +minimize, within economical and practical range, the total number of +weighings or measurements necessary. Consequently, no strict time of +interval between individual weighings or measurements can be given in +this case. It may be said, however, that it is not desirable to take +these at anything less than five-minute intervals. Under ordinary +circumstances a three- to five-minute interval is sufficient in the case +of all steam-pressure, vacuum--including mercurial columns and +barometer--superheat and temperature readings. + + +Gland and Hot-Well Regulation + +There are two highly important features requiring more or less constant +attention throughout a test, namely the gland and hot-well regulation. +For the present purpose we may assume that the glands are supplied with +either steam or water for sealing them. All steam supplied to the +turbine obviously goes to swell the hot-well contents, and to thus +increase the total steam consumption. The ordinary steam gland is in +reality a pressure gland. At both ends of the turbine casing is an +annular chamber, surrounding the turbine spindle at the point where it +projects through the casing. A number of brass rings on either side of +this chamber encircle the spindle, with only a very fine running +clearance between the latter and themselves. Steam enters the gland +chamber at a slight pressure, and, when a vacuum exists inside the +turbine casing, tends to flow inward. The pressure, however, inside the +gland is increased until it exceeds that of the atmosphere outside, and +by maintaining it at this pressure it is obvious that no air can +possibly enter the turbine through the glands, to destroy the vacuum. +The above principle must be borne in mind during a test upon a turbine +having steam-fed glands. Perhaps the best course to follow--in view of +the economy of gland steam consumption necessary--is as follows: + +During the preliminary non-test run, full steam is turned into both +glands while the vacuum is being raised, and maintained until full load +has been on the turbine for some little time. The vacuum will by this +time have probably reached its maximum, and perhaps fallen to a point +slightly lower, at which hight it may be expected to remain, other +conditions also remaining constant. The gland steam must now be +gradually turned off until the amount of steam vapor issuing from the +glands is almost imperceptible. This should not lower the vacuum in the +slightest degree. By gradual degrees the gland steam can be still +farther cut down, until no steam vapor at all can be discerned issuing +from the gland boxes. This reduction should be continued until a point +is reached at which the vacuum is affected, when it must be stopped and +the amount of steam flowing to the gland again increased very slightly, +just enough to bring the vacuum again to its original hight. The steam +now passing into the glands is the minimum required under the +conditions, and should be maintained as nearly constant as possible +throughout the test. Practically all steam entering the glands is drawn +into the turbine, and thence to the condenser, and under the +circumstances it may be assumed the increase in steam consumption +arising from this source is also a minimum. + +There is one mechanical feature which has an important bearing upon the +foregoing question, and which it is one of the tester's duties to +investigate. This is illustrated in Fig. 71, which shows a turbine +spindle projecting through the casing. The gland box is let into the +casing as shown. Brass rings A calked into the gland box encircle the +shaft on either side of the annular steam space S. As the clearance +between the turbine spindle and the rings A is in a measure instrumental +in determining the amount of steam required to maintain a required +pressure inside the chamber, it is obvious that this clearance should be +minimum. An unnecessarily large clearance means a proportionally large +increase in gland steam consumption and _vice versa_. + +[Illustration: FIG. 71] + +When the turbine glands are sealed with water, all water leakage which +takes place into the turbine, and ultimately to the condenser hot-well, +must be measured and subtracted from the hot-well contents at the end of +a test. + +The foregoing remarks would not apply to those cases in which the gland +supply is drawn from and returned to the hot-well, or a pipe leading +from the hot-well. Then no correction would be necessary, as all water +used for gland purposes might be assumed as being taken from the +measuring tanks and returned again in time for same or next weighing or +measurement. + + +General Considerations + +There are a few principal elementary points which it is necessary always +to keep in mind during the conduct of a test. Among these are the +effects of variation in vacuum, superheat, initial steam pressure, and, +as already indicated, in load. There exist many rules for determining +the corrections necessitated by this variation. For example, it is often +assumed that 9 degrees Fahrenheit, excess or otherwise, above or below +that specified, represents an increase or reduction in efficiency of +about 1 per cent. It is probable that the percentage increase or +decrease in steam consumption, in the case of superheat, can be more +reliably calculated than in other cases, as, for example, vacuum; but +the increase cannot be said to be due solely to the variation in +superheat. In other words, the individuality of the particular turbine +being tested always contributes something, however small this something +may be, to the results obtained. + +These remarks are particularly applicable where vacuum is concerned. +Here again rules exist, one of these being that every additional inch of +vacuum increases the economy of the turbine by something slightly under +half a pound of steam per kilowatt-hour. But a moment's consideration +convinces one of the utter unreliability of such rules for general +application. It is, for instance, well known that many machines, when +under test, have demonstrated that the total increase in the water rate +is very far from constant. A machine tested, for example, gave +approximately the following results, the object of the test being to +discover the total increase in the water rate per inch decrease in +vacuum: + +From 27 inches to 26 inches, 4.5 per cent. + +From 26.2 inches to 24.5 inches, 2.5 per cent. + +This illustrates to what an extent the ratio of increase can vary, and +it must be borne in mind that it is very probable that the variation is +different in different types and sizes of machines. + +There can exist, therefore, no empirical rules of a reliable nature upon +which the tester can base his deductions. The only way calculated to +give satisfaction is to conduct a series of preliminary tests upon the +turbine undergoing observation, and from these to deduce all information +of the nature required, which can be permanently recorded in a set of +curves for reference during the final official tests. + +In conclusion, it must be admitted that many published tests outlining +the performances of certain makes of turbine are unreliable. To +determine honestly the capabilities of any machine in the direction of +steam economy is an operation requiring time, and unbiased and accurate +supervision. By means of such assets as "floating quantities," short +tests during exceptionally favorable conditions, and disregard of the +vital necessity of running a test under the proper specified conditions, +it is comparatively easy to obtain results apparently highly +satisfactory, but which under other conditions might be just the +reverse. These considerations are, however, unworthy of the tester +proper. + + + + +VII. AUXILIARIES FOR STEAM TURBINES[6] + +[6] Contributed to _Power_ by Thomas Franklin. + + +The Jet Condenser + +The jet condenser illustrated in Fig. 72 is singularly well adapted for +the turbine installation. As the type has not been so widely adopted as +the more common forms of jet condenser and the surface types, it may +prove of interest to describe briefly its general construction and a few +of its special features in relation to tests. + +[Illustration: FIG. 72] + +Referring to the figure, C is the main condenser body. Exhaust steam +enters at the left-hand side through the pipe E, condensing water +issuing through the pipe D at the opposite side. Passing through the +short conical pipe P, the condensing water enters the cylindrical +chamber W and falls directly upon the spraying cone S. The hight of this +spraying cone is determined by the tension upon the spring T, below the +piston R, the latter being connected to the cone by a spindle L. An +increase of the water pressure inside the chamber W will thus compress +the spring, and the spraying cone being consequently lowered increases +the aperture between it and the sloping lower wall of the chamber W, +allowing a greater volume of water to be sprayed. The piston R +incidentally prevents water entering the top vapor chamber V. From the +foregoing it can be seen that this condenser is of the contra-flow type, +the entering steam coming immediately into contact with the sprayed +water. The perforated diaphragm plate F allows the vapor to rise into +the chamber V, from which it is drawn through the pipe A to the air +pump. A relief valve U prevents an excessive accumulation of pressure +in the vapor chamber, this valve being obviously of delicate +construction, capable of opening upon a very slight increase of the +internal pressure over that of the atmosphere. Condensed steam and +circulating water are together carried down the pipe B to the well Z, +from which a portion may be carried off as feed water, and the remainder +cooled and passed through the condenser again. Under any circumstances, +whether the air pump is working or not, a certain percentage of the +vapor in the condenser is always carried down the pipe B, and this +action alone creates a partial vacuum, thus rendering the work of the +air pump easier. As a matter of fact, a fairly high vacuum can be +maintained with the air pump closed down, and only the indirect pumping +action of the falling water operating to rarify the contents of the +condenser body. It is customary to place the condenser forty or more +feet above the circulating-water pump, the latter usually being a few +feet below the turbine. + + +Features Demanding Attention + +When operating a condenser of this type, the most important features +requiring preliminary inspection and regulation while running are: + +(a) Circulating-water regulation. + +(b) Freedom of all mechanical parts of spraying mechanism. + +(c) Relief-valve regulation. + +(d) Water-cooling arrangements. + +The tester will, however, devote his attention to a practical survey of +the condenser and its auxiliaries, before running operations commence. + +A preliminary vacuum test ought to be conducted upon the condenser body, +and the exhaust piping between the condenser and turbine. To accomplish +this the circulating-water pipe D can be filled with water to the +condenser level. The relief valve should also be water-sealed. Any +existing leakage can thus be located and stopped. + +Having made the condenser as tight as possible within practical limits, +vacuum might be again raised and, with the same parts sealed, allowed to +fall slowly for, say, ten minutes. A similar test over an equal period +may then be conducted with the relief valve not water-sealed. A +comparison of the times taken for an equal fall of vacuum in inches, +under the different conditions, during the above two tests, will reveal +the extent of the leakage taking place through the relief valve. It +seems superfluous to add that the fall of vacuum in both the foregoing +tests must not be accelerated in any way, but must be a result simply of +the slight inevitable leakage which is to be found in every system. + +On a comparatively steady load, and with consequently only small +fluctuation in the volume of steam to be condensed, the conditions are +most favorable for regulating the amount of circulating water necessary. +Naturally, an excess of water above the required minimum will not affect +the pressure conditions inside the condenser. It does, however, increase +the quantity of water to be handled from the hot-well, and incidentally +lowers the temperature there, which, whether the feed-water pass through +economizers or otherwise, is not advisable from an economical +standpoint. Thus there is an economical minimum of circulating water to +be aimed at, and, as previously stated, it can best be arrived at by +running the turbine under normal load and adjusting the flow of the +circulating water by regulating the main valve and the tension upon the +spring T. Under abnormal conditions, the breakdown of an air pump, or +the sudden springing of a bad leak, for instance, the amount of +circulating water can be increased by a farther opening of the main +valve if necessary, and a relaxation of the spring tension by hand; or, +the spring tension might be automatically changed immediately upon the +vacuum falling. + +The absolute freedom of all moving parts of the spraying mechanism +should be one of the tester's first assurances. To facilitate this, it +is customary to construct the parts, with the exception of the springs, +of brass or some other non-corrosive metal. The spraying cone must be +thoroughly clean in every channel, to insure a well-distributed stream +of water. Nor is it less important that careful attention be given to +the setting and operation of the relief valve, as will be seen later. +The obvious object of such a valve is to prevent the internal condenser +pressure ever being maintained much higher than the atmospheric +pressure. A number of carefully designed rubber flap valves, or one +large one, have been found to act successfully for this purpose, +although a balanced valve of more substantial construction would appear +to be more desirable. + + +Importance of Relief Valves + +The question of relief valves in turbine installations is an important +one, and it seems desirable at this point to draw attention to another +necessary relief valve and its function, namely the turbine atmospheric +valve. As generally understood, this is placed between the turbine and +condenser, and, should the pressure in the latter, owing to any cause, +rise above that of the atmosphere, it opens automatically and allows the +exhaust steam to flow through it into the atmosphere, or into another +condenser. + +A general diagrammatic arrangement of a steam turbine, condenser, and +exhaust piping is shown in Fig. 73. Connected to the exhaust pipe B, +near to the condenser, is the automatic atmospheric valve D, from which +leads the exhaust piping E to the atmosphere. The turbine relief valve +is shown at F, and the condenser relief valve at G. The main exhaust +valve between turbine and condenser is seen at H. We have here three +separate relief valves: one, F, to prevent excessive pressure in the +turbine: the second, D, an atmospheric valve opening a path to the air, +and, in addition to preventing excessive pressure accumulating, also +helping to keep the temperature of the condenser body and tubes low; the +third, the condenser relief valve G, which in itself ought to be capable +of exhausting all steam from the turbine, should occasion demand it. + +[Illustration: FIG. 73] + +Assuming a plant of this description to be operating favorably, the +conditions would of necessity be as follows: The valves F, D, and G, all +closed; the valve H open. Suppose that, owing to sudden loss of +circulating water, the vacuum fell to zero. The condenser would at once +fill with steam, a slight pressure would be set up, and whichever of the +three valves happened to be set to blow off at the lowest pressure would +do so. Now it is desirable that the first valve to open under such +circumstances should be the atmospheric valve D. This being so, the +condenser would remain full of steam at atmospheric pressure until the +attendant had had time to close the main hand-or motor-operated exhaust +valve H, which he would naturally do before attempting to regain the +circulation of the condensing water. Again, assume the installation to +be running under the initial conditions, with the atmospheric valve D +and all remaining valves except H closed. + +Suppose the vacuum again fell to zero from a similar cause, and, +further, suppose the atmospheric valve D failed to operate +automatically. The only valves now capable of passing the exhaust steam +are the turbine and condenser relief valves F and G. Inasmuch as the +pressures at exhaust in the turbine proper, on varying load, vary over a +considerably greater range than the small fairly constant absolute +pressures inside the condenser, it is obviously necessary to allow for +this factor in the respective setting of these two relief valves. In +other words, the obvious deduction is to set the turbine relief valve to +blow off at a higher pressure than the condenser relief valve, even +when considering the question with respect to condensing conditions +only. In this second hypothetical case, then, with a closed and disabled +atmospheric valve, the exhaust must take place through the condenser, +until the turbine can be shut down, or the circulating water regained +without the former course being found necessary. + +There is one other remote case which may be assumed, namely, the +simultaneous refusal of both atmospheric and condenser relief valves to +open, upon the vacuum inside the condenser being entirely lost. The +exhaust would then be blown through the turbine relief valve F, until +the plant could be closed down. + +Although the conditions just cited are highly improbable in actual +practice, it can at once be seen that to insure the safety of the +condenser, absolutely, the turbine relief valve must be set to open at a +comparatively low pressure, say 40 pounds by gage, or thereabouts. To +set it much lower than this would create a possibility of its leaking +when the turbine was making a non-condensing run, and when the pressure +at the turbine exhaust end is often above that of the atmosphere. From +every point of view, therefore, it is advisable to make a minute +examination of all relief valves in a system, and before a test to +insure that these valves are all set to open at their correct relative +pressures. + +It must be admitted that the practice of placing a large relief valve +upon a condenser in addition to the atmospheric exhausting valve is by +no means common. The latter valve, where surface condensing is adopted, +is often thought sufficient, working in conjunction with a quickly +operated main exhaust valve. Similarly, with a barometric condenser as +that illustrated in Fig. 72, the atmospheric exhaust valve D (seen in +Fig. 73) is sometimes dispensed with. This course is, however, +objectionable, for upon a loss of vacuum in the turbine, all exhaust +steam must pass through the condenser body, or the entire plant be +closed down until the vacuum is regained. The simple construction of the +barometric condenser, however, is in such an event much to its +advantage, and the passage of the hot steam right through it is not +likely to seriously warp or strain any of its parts, as might probably +happen in the case of a surface condenser. + +The question of the advisability of thus adding to a plant can only be +fairly decided when all conditions, operating and otherwise, are fully +known. For example, if we assume a large turbine to be operating on a +greatly varying load, and exhausting into a condenser, as that in Fig. +72, and, further, having an adequate stand-by to back it up, one's +obvious recommendation would be to equip the installation with both a +condenser relief valve and an atmospheric valve, in addition, of course, +to the main exhaust valve, which is always placed between the +atmospheric valve and condenser. There are still other considerations, +such as water supply, condition of circulating water, style of pump, +etc., which must all necessarily have an obvious bearing upon the +settlement of this question; so that generalization is somewhat out of +place, the final design in all cases depending solely upon general +principles and local conditions. + + +Other Necessary Features of a Test + +In connection with the condenser, of any type, and its auxiliaries, +there remain a few necessary examinations and operations to be +conducted, if it is desired to obtain the very best results during the +test. It will be sufficient to just outline them, the method of +procedure being well known, and the requirement of any strict routine +being unnecessary. These include: + +(1) A thorough examination of the air-pump, and, if possible, an equally +careful examination of diagrams taken from it when running on full +load. Also careful examination of the piping, and of any other +connections between the air pump and condenser, or other auxiliaries. It +will be well in this examination to note the general "lay" of the air +pipes, length, hight to which they rise above condenser and air pump, +facilities for drainage, etc., as this information may prove valuable in +determining the course necessary to rectify deficiencies which may later +be found to exist. + +(2) In a surface condenser, inspection of the pumps delivering condensed +steam to the measuring tanks or hot-well; inspection of piping between +the condenser and the pump, and also between the pump and measuring +tanks. If these pumps are of the centrifugal type it is essential to +insure, for the purposes of a steam-consumption test, as much regularity +of delivery as possible. + +(3) In the case of a consumption test upon a turbine exhausting into a +barometric condenser, and where the steam consumed is being measured by +the evaporation in the boiler over the test period, time must be devoted +to the feed-pipes between the feed-water measuring meter or tank and the +boilers. Under conditions similar to those operating in a plant such as +that shown in Fig. 72, the necessary boiler feed might be drawn from the +hot-well, the remainder of the hot-well contents probably being pumped +through water coolers, or towers, for circulating through the condenser. +With the very best system, it is possible for a slight quantity of oil +to leak into the exhaust steam, and thence to the hot-well. In its +passage, say along wooden conduits, to the measuring tank or meter, this +water would probably pass through a number of filters. The efficiency of +these must be thoroughly insured. It is unusual, in those cases where a +simple turbine steam-consumption test is being carried out, and not an +efficiency test of a complete plant, to pass the measured feed-water +through economizers. Should the latter course, owing to special +conditions, become necessary, a careful examination of all economizer +pipes would be necessary. + +(4) The very careful examination of all thermometer pockets, steam- and +temperature-gage holes, etc., as to cleanliness, non-accumulation of +scale, etc. + + +Special Auxiliaries Necessary + +Having outlined the points of interest and importance in connection with +the more permanent features of a plant, we arrive at the preparation and +fitting of those special auxiliaries necessary to carry on the test. + +[Illustration: FIG. 74] + +It is customary, when carrying out a first test, upon both prime mover +and auxiliaries, to place every important stage in the expansion in +communication with a gage, so that the various pressures may be recorded +and later compared with the figures of actual requirement. To do this, +in the case of the turbine, it is necessary to bore holes in the cover +leading to the various expansion chambers, and into each of these holes +to screw a short length of steam pipe, having preferably a loop in its +length, to the other end of which the gage is attached. Fig. 74 +illustrates, diagrammatically, a complete turbine installation, and +shows the various points along the course taken by the steam at which it +is desirable to place pressure gages. The figure does not show the +high-pressure steam pipe, nor any of the turbine valves. With regard to +these, it will be desirable to place a steam gage in the pipe, +immediately before the main stop-valve, and another immediately after +it. Any fall of pressure between the two sides of the valve can thus be +detected. To illustrate this clearly, Fig. 75 is given, showing the +valves of a turbine, and the position of the gages connected to them. +The two gages E and F on either side of the main stop-valve A are also +shown. The steam after passing through the valve, which, in the case of +small turbines, is hand-operated, goes in turn through the automatic +stop-valve B, the function of which is to automatically shut steam off +should the turbine attain a predetermined speed above the normal, the +steam strainer C, and finally through the governing valve D into the +turbine. As shown, gages G and H are also fitted on either side of the +strainer, and these, in conjunction with gages E and F, will enable any +fall in pressure between the first two valves and the governing valve to +be found. Up to the governing-valve inlet no throttling of the steam +ought to take place under normal conditions, i.e., with all valves open, +and consequently any fall in pressure between the steam inlet and this +point must be the result of internal wire-drawing. By placing the gages +as shown, the extent to which this wire-drawing affects the pressures +obtainable can be discovered. + +[Illustration: FIG. 75] + +On varying and even on normal and steady full load, the steam is more or +less reduced in pressure after passing through the governing valve D; a +gage I must consequently be placed between the valve, preferably on the +valve itself, and the turbine. Returning to Fig. 74, the gages shown are +A, B, C, D, and E, connected to the first, second, third, fourth, and +fifth expansions; also F in the turbine and exhaust space, where there +are no blades, G in the exhaust pipe immediately before the main exhaust +valve E (see Fig. 73), and H connected to the condenser. On condensing +full load it is probable that A, B, and C will all register pressures +above the atmosphere, while gages D, E, F, and G will register pressures +below the atmosphere, being for this purpose vacuum gages. On the other +hand, with a varying load, and consequently varying initial pressures, +one or two of the gages may register pressure at one moment and vacuum +at another. It will therefore be necessary to place at these points +compound gages capable of registering both pressure and vacuum. With the +pressures in the various stages constantly varying, however, a gage is +not by any means the most reliable instrument for recording such +variations. The constant swinging of the finger not only renders +accurate reading at any particular moment both difficult and, to an +extent, unreliable, but, in addition, the accompanying sudden changes of +condition, both of temperature and pressure, occurring inside the gage +tube, in a comparatively short time permanently warp this part, and thus +altogether destroy the accuracy of the gage. It is well known that even +with the best steel-tube gages, registering comparatively steady +pressures, this warping of the tube inevitably takes place. The quicker +deterioration of such gage tubes, when the gage is registering quickly +changing pressures, can therefore readily be conceived, and for this +reason alone it is desirable to have all gages, whatever the conditions +under which they work, carefully tested and adjusted at short intervals. +If it is desired to obtain reliable registration of the several +pressures in the different expansions of a turbine running on a varying +load, it would therefore seem advisable to obtain these by some type of +external spring gage (an ordinary indicator has been found to serve well +for this purpose) which the sudden internal variations in pressure and +temperature cannot deleteriously affect. + +In view of the great importance he must attach to his gage readings, the +tester would do well to test and calibrate and adjust where necessary +all the gages he intends using during a test. This he can do with a +standard gage-testing outfit. By this means only can he have full +confidence in the accuracy of his results. + +In like manner it is his duty personally to supervise the connecting and +arrangement of the gages, and the preliminary testing for leakage which +can be carried out simultaneously with the vacuum test made upon the +turbine casing. + + +Where Thermometers are Required + +Equally important with the foregoing is the necessity of calibrating and +testing of all thermometers used during a test. Where possible it is +advisable to place new thermometers which have been previously tested +at all points of high temperature. Briefly running them over, the points +at which it is necessary to place thermometers in the entire system of +the steam and condensing plant are as follows: + +(1) A thermometer in the steam pipe on the boiler, where the pipe leaves +the superheater. + +(2) In the steam pipe immediately in front of the main stop-valve, near +point E in Fig. 75. + +(3) In the main governing valve body (see I, Fig. 75) on the inlet side. + +(4) In the main governing valve body on the turbine side, which will +register temperatures of steam after it has passed through the valve. + +(5) In the steam-turbine high-pressure chamber, giving the temperature +of the steam before it has passed through any blades. + +(6) In the exhaust chamber, giving the temperature of steam on leaving +the last row of blades. + +(7) In the exhaust pipe near the condenser. + +(8) In the condenser body. + +(9) In the circulating-water inlet pipe close to the condenser. + +(10) In the circulating-water outlet pipe close to the condenser. + +(11) In the air-pump suction pipe close to the condenser. + +(12) In the air-pump suction pipe close to the air pump. + +It is not advisable to place at those vital points, the readings at +which directly or indirectly affect the consumption, two thermometers, +say one ordinary chemical thermometer and one thermometer of the gage +type, thus eliminating the possibility of any doubt which might exist +were only one thermometer placed there. + +There is no apparent reason why one should attempt to take a series of +temperature readings during a consumption test on varying load. The +temperatures registered under a steady load test can be obtained with +great reliability, but on a varying load, with constantly changing +temperatures at all points, this is impossible. This is, of course, +owing to the natural sluggishness of the temperature-recording +instruments, of whatever class they belong to, in responding to changes +of condition. As a matter of fact, the possibility of obtaining +correctly the entire conditions in a system running under greatly +varying loads is very doubtful indeed, and consequently great reliance +cannot be placed upon figures obtained under such conditions. + +A few simple calculations will reveal to the tester his special +requirements in the direction of measuring tanks, piping, etc., for his +steam consumption test. Thus, assuming the turbine to be tested to be of +3000 kilowatt capacity normal load, with a guaranteed steam consumption +of, say, 14.5 pounds per kilowatt-hour, he calculates the total water +rate per hour, which in this case would be 43,500 pounds, and designs +his weighing or measuring tanks to cope with that amount, allowing, of +course, a marginal tank volume for overload requirements. + + + + +VIII. TROUBLES WITH STEAM TURBINE AUXILIARIES[7] + +[7] Contributed to _Power_ by Walter B. Gump. + + +The case about to be described concerns a steam plant in which there +were seven cross-compound condensing Corliss engines, and two Curtis +steam turbines. The latter were each of 1500-kilowatt capacity, and were +connected to surface condensers, dry-vacuum pumps, centrifugal, hot-well +and circulating pumps, respectively. In the illustration (Fig. 76), the +original lay-out of piping is shown in full lines. Being originally a +reciprocating plant it was difficult to make the allotted space for the +turbines suitable for their proper installation. The trouble which +followed was a perfectly natural result of the failure to meet the +requirements of a turbine plant, and the description herein given is but +one example of a great many where the executive head of a concern +insists upon controlling the situation without regard to engineering +advice or common sense. + +[Illustration: FIG. 76. TURBINE AUXILIARIES AND PIPING] + + +Circulating Pump Fails to Meet Guarantee + +Observing the plan view, it will be seen that the condensers for both +turbines receive their supply of cooling water from the same supply +pipe; that is, the pipes, both suction and discharge, leading to No. 1 +condenser are simply branches from No. 2, which was installed first +without consideration for a second unit. When No. 1 was installed there +was a row of columns from the basement floor to the main floor extending +in a plane which came directly in front of the condenser. The column P +shown in the plan was so located as to prevent a direct connection +between the centrifugal circulating pump and the condenser inlet. The +centrifugal pump was direct-connected to a vertical high-speed engine, +and the coupling is shown at E in the elevation. + +Every possible plan was contemplated to accommodate the engine and pump +without removing any of the columns, and the arrangement shown was +finally adopted, leaving the column P in its former place by employing +an S-connection from the pump to the condenser. It should be stated that +the pump was purchased under a guarantee to deliver 6000 gallons per +minute under a head of 50 feet, with an impeller velocity of 285 +revolutions per minute. The vertical engine to which the pump was +connected proved to be utterly unfit for running at a speed beyond 225 +to 230 revolutions per minute, and in addition the S-bend would +obviously reduce the capacity, even at the proper speed of the impeller. + +Besides these factors there was another feature even more serious. It +was found that when No. 2 unit was operating No. 1 could not get as +great a quantity of circulating water as when No. 2 was shut down. This +was because No. 2 was drawing most of the water, and No. 1 received only +that which No. 2 could not pull from the suction pipe A. This will be +clear from the fact that the suction and discharge pipes for No. 1 were +only 16 inches, while those of No. 2 were 20 inches and 16 inches, +respectively. The condenser for No. 2 had 1000 square feet less cooling +surface than No. 1, which had 6000 square feet and was supplied with +cooling water by means of two centrifugal pumps of smaller capacity +than for No. 1 and arranged in parallel. These were each driven by an +electric motor, and were termed "The Siamese Twins," due to the way in +which they were connected. + +The load factor of the plant ranged from 0.22 to 0.30, the load being +almost entirely lighting, so that for the winter season the load factor +reached the latter figure. The day load was, therefore, light and not +sufficient to give one turbine more than from one-fourth to one-third +its rated capacity. Under these conditions No. 1 unit was able to +operate much more satisfactorily than when fully loaded, because of the +fact that the cooling water was more effective. This was, of course, all +used by No. 1 unit when No. 2 was not operating. At best, however, it +was found that the vacuum could not be made to exceed 24 inches, and +during the peak, with the two turbines running, the vacuum would often +drop to 12 inches. A vacuum of 16 inches or 18 inches on the peak was +considered good. + + +An Investigation + +Severe criticism "rained" heavily upon the engineer in charge, and +complaints were made in reference to the high oil consumption. An +investigation on the company's part followed, and the firm which +furnished the centrifugal pump and engine was next in order to receive +complaints. Repeated efforts were made to increase the speed of the +vertical engine to 285 revolutions per minute, but such a speed proved +detrimental to the engine, and a lower speed of about 225 revolutions +per minute had to be adopted. + +A thorough test on the pump to ascertain its delivery at various speeds +was the next move, and a notched weir, such as is shown in the +elevation, was employed. The test was made on No. 2 cooling tower, not +shown in the sketch, and showed that barely 3000 gallons per minute were +being delivered to the cooling tower. While the firm furnishing the pump +was willing to concede that the pump might not be doing all it should, +attention was called to the fact that there might be some other +conditions in connection with the system which were responsible for the +losses. Notable among these was the hydraulic friction, and when this +feature of the case was presented, the company did not seem at all +anxious to investigate the matter further; obviously on account of +facing a possible necessity for new piping or other apparatus which +might cost something. + +Approximately 34 feet was the static head of water to be pumped over No. +2 cooling tower. Pressure gages were connected to the suction, +discharge, and condenser inlet, as shown at G, G' and G'' respectively. +When No. 1 unit was operating alone the gage G showed practically zero, +indicating no vacuum in the suction pipe. Observing the same gage when +No. 2 unit was running, a vacuum as high as 2 pounds was indicated, +showing that No. 2 was drawing more than its share of cooling water from +the main A and hence the circulating pump for No. 1 was fighting for all +it received. Gage G' indicated a pressure of 21 pounds, while G'' +indicated 18.5 pounds, showing a difference of 2.5 pounds pressure lost +in the S-bend. This is equivalent to a loss of head of nearly 6 feet, +0.43 pound per foot head being the constant employed. The total head +against which the pump worked was therefore + + G' + G = 21 + 2, +or + 23 + ---- = 53 + 0.43 + +feet approximately. Since the static head was 34 feet, the head lost in +friction was evidently + + 53-34 = 19 +feet, or + 1900 + ---- = 36 + 53 + +per cent., approximately. + + +Supply of Cooling Water Limited + +In addition to this the supply of cooling water was limited, the vacuum +being extremely low at just the time when efficient operation should be +had. The natural result occurred, which was this: As the load on the +turbine increased, the amount of steam issuing into the condenser +increased, beating [Transcriber: heating?] the circulating water to a +temperature which the cooling tower (not in the best condition) was +unable to decrease to any great extent. The vacuum gradually dropped +off, which indicated that the condenser was being filled with vapor, and +in a short time the small centrifugal tail-pump lost its prime, +becoming "vapor bound," and the vacuum further decreased. The steam +which had condensed would not go into the tail-pump because of the +tendency of the dry-pump to maintain a vacuum. When a certain point was +reached the dry-vacuum pump started to draw water in its cylinder, and +the unit had to be shut down immediately. + + +Vapor-bound Pumps + +As the circulating water gradually rose in temperature the circulating +pump also became "vapor bound," so that the unit would be tied up for +the rest of the night, as this pump could not be made to draw hot water. +The reason for this condition may be explained in the following way. +When the circulating pump was operating and there was a suction of 2 +pounds indicated at G, the water was not flowing to the pump of its own +accord, but was being pulled through by force. This water would flow +through the pump until a point was reached when the water became hot +enough to be converted into vapor, this occurring at a point where the +pressure was sufficiently reduced to cause the water to boil. Naturally +this point was in the suction pipe and vapor was thus maintained behind +the pump as long as it was operating. In this case the pump was merely +maintaining a partial vacuum, but not drawing water. After the vacuum +was once lost, by reason of the facts given, it could not be regained, +as the circulating water, piping and condenser required a considerable +period of time in which to cool. + +Before any radical changes were made it was decided that a man should +crawl in the suction pipe A, and remove such sand, dirt, or any other +obstacles as were believed to cause the friction. After this had been +done and considerable sand had been removed, tests were resumed with +practically the same results as before. The investigation was continued +and the dry-vacuum pumps were overhauled, as they had been damaged by +water in the cylinders, and furthermore needed re-boring. In short, the +auxiliaries were restored to the best condition that could be brought +about by the individual improvement of each piece of apparatus. As this +was not the seat of the trouble, however, the remedy failed to effect a +"cure." It was demonstrated that the steam consumption of the turbines +was greatly increased due to priming of the boilers, as well as +condensation in the turbine casing; hence, the ills above mentioned were +aggravated. + + +Changes in Piping + +After a great deal of argument from the chief engineer, and the firm +which furnished the pump, both making a strong plea for a change in the +piping, the company accepted the inevitable, and the dotted portion +shows the present layout. The elbow M was removed, and a tee put in its +place to which the piping D was connected. The circulating pump was +removed to the position shown, and a direct connection substituted for +the S-bend. The discharge pipe C was carried from No. 1 unit separately, +as shown in the elevation, and terminated at No. 1 cooling tower +instead of No. 2, which shortened the distance about 60 feet, the total +length of pipe (one way) from No. 1 unit being originally 250 feet. In +this way the condensing equipment was made practically separate for each +turbine, as it should have been in the first place. + +With the new piping a vacuum of 24 inches on the peak could be reached. +While this is far from an efficient value, yet it is better than the +former figure. The failure to reach a vacuum of 28 inches or better is +due primarily to a lack of cooling water, but an improvement in this +regard could be made by reconstructing the cooling towers, which at +present do not offer the proper amount of cooling surface. The screens +used were heavy galvanized wire of about 3/16-inch mesh, which became +coated in a short time, and must be thoroughly cleaned to permit the +water to drop through them. The supply of cooling water was taken from a +30-inch pipe line several miles long and fed from a spring. The amount +of water varied considerably and was at times quite insufficient for the +load on the plant. Instead of meeting this condition with the best +apparatus possible, a chain of difficulties were added to it, with the +results given. + + + + +INDEX + + +Acceleration, rate of, 147 + +Adjustment, axial, 65 + making, 66 + +Air-pump, examining, 163 + +Allis-Chalmers Co. steam turbine, 41 + +Auxiliaries, 2, 154 + special, 165 + +Auxiliary plant for consumption test, 137 + spring on governor dome, 28 + +Axial adjustment, 65 + + +Baffler, 36 + functions, 39 + +Bearings, main, 69 + +Blades, construction details, 44 + inspecting, 104 + +Blading, Allis-Chalmers turbine, 48 + Westinghouse-Parsons turbine, 59, 92 + +Blueprints, studying, 11 + +Buckets, moving, 14 + stationary, 14 + +Bushings, 36 + + +Carbon packing, 19 + ring, 20 + +Central gravity oiling system, 111 + +Circulating pump fails to meet guarantee, 172 + +Clearance, 15, 150 + adjusting, 18 + between moving and stationary buckets, 4 + gages, 17 + measuring, 18 + radial, 63 + +Comma lashing, 95 + +Condensers, 108, 131 + jet, 154 + +Conditions for successful operation, 105 + +Cooling water supply limited, 177 + +Coupling, 127 + +Cover-plate, 4 + -plate, lowering, 9 + +Curtis turbine, 11 + turbine in practice, 1 + setting valves, 31, 32 + + +De Laval turbines, 118 + +Draining system, 105 + +Dummy leakage, 115 + pistons, 63, 65 + rings, 43, 113, 114 + + +Equalizing pipes, 64 + +Exhaust end of turbine, 107 + pipe, 107 + +Expanding nozzles, 14 + + +Feed-pipes, 164 + +Flow, rate, 38 + +Foundation drawings, 2 + rings, 44, 46 + +Fourth-stage wheel, 14 + +Franklin, Thomas, 112, 137, 154 + + +Gages, calibrating and adjusting, 169 + clearance, 17 + for test work, 165 + +Generator, 53 + +Glands, examination for scale, 104 + packing, 71, 77 + regulation, 148 + +Governor, Allis-Chalmers turbine, 48 + Curtis turbine, 27, 31 + improved, Westinghouse-Parsons turbine, 83 + -rods, adjusting, 35 + safety-stop, 86 + Westinghouse-Parsons turbine, 80 + +Grinding, 38 + +Guide-bearing, lower, 9 + +Gump, Walter B., 172 + + +Holly draining system, 106 + +Horseshoe shim, 8 + +Hot-well regulation, 148 + + +Inspection, 103 + +Intermediate, 14 + + +Jacking ring, 8 + +Jet condenser, 154 + +Johnson, Fred L., 1, 31 + + +Leakage, 118 + +Load variation, 144 + +Lower guide-bearing, 9 + +Lubrication, 51 + + +Measuring tanks, 171 + +Mechanical valve-gear, 32 + + +Nozzles, expanding, 14 + + +Oil, 57, 103, 109 + amount passing through bearings, 122 + consumption, high, 175 + detecting water in, 122 + pressure, 122 + -temperature curve, 123 + +Oil, testing, 110 + velocity of flow, 122 + +Oiling, 87 + system, importance, 119 + +Operation, Allis-Chalmers turbine, 54, 55 + successful, 105 + +Operations in handling turbine plant, 146 + +Overload valve, 28 + + +Packing, carbon, 19 + glands, 71 + ring, self-centering, 14 + +Parsons type of turbine, 41 + +Passage in foundation, 2 + +Peep-holes, 15, 18 + +Piping, 171 + changing, 179 + inspection, 164 + +Pressure, 63 + gages, 166 + in glands, 57 + +Pump, circulating, fails to meet guarantee, 172 + inspection, 164 + + +Radial clearance, 63 + +Rateau turbines, 118 + +Relief valves, 31 + valves, importance, 159 + +Ring, carbon, 20 + +Rotor, Westinghouse-Parsons turbine, 59 + +Running, 99 + + +Safety-stop, 22 + -stop governor, 86 + +Saucer steps, 39 + +Screw, step-bearing, 18 + step-supporting, 4 + +Separators, 105 + +Setting spindle and cylinder for minimum leakage, 115 + valves in Curtis turbine, 31, 32 + +Shaft, holding up while removing support, 8 + +Shield-plate, 26, 36 + +Shim, horseshoe, 8 + +Shroud rings, 44, 46 + +Shrouding on buckets and intermediates, 18 + +Shutting down, 101 + +Special turbine features, 127 + +Spindle, lifting, 96 + removing, 104 + +Spraying mechanism, 158 + +Stage valves, 28, 31 + +Starting up, 54, 95 + +Step-bearing, lowering to examine, 8 + -bearing screw, 18 + -blocks, 4 + -lubricant, 4 + -pressure, 38 + -supporting screw, 4 + -water, flow, 38 + +Stopping turbine, 56 + +Sub-base, 8 + +Superheated steam, 105 + + +Test loads, 141 + necessary features, 163 + +Testing oil, 110 + preparing turbine for, 145 + steam turbine, 112, 137, 152 + +Thermometer, calibrating and testing, 169 + oil, 125 + +Thrust-block, 118 + +Top block, 4 + +Troubles with steam turbine auxiliaries, 172 + +Turbine features, special, 127 + + +Vacuum, 152 + raising, 107 + test, 135 + +Valve-gear, 83 + -gear, mechanical, 22, 32 + operation during consumption test, 138 + overload, 28 + relief, 31 + importance, 159 + setting in Curtis turbine, 31, 32 + stage, 28,31 + +Vapor bound pumps, 178 + + +Water, cooling, limited, 177 + in oil, detecting, 122 + -measurement readings, 148 + pressure, 101 + service, 126 + importance, 119 + tests of condenser, 133 + used in glands, 57, 76 + +Westinghouse-Parsons steam turbine, 58 + +Wheels, 14 + lower or fourth-stage, 14 + position, 18 + + + + + +End of the Project Gutenberg EBook of Steam Turbines, by Hubert E. 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