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diff --git a/27687.txt b/27687.txt new file mode 100644 index 0000000..fbcce9e --- /dev/null +++ b/27687.txt @@ -0,0 +1,4271 @@ +The Project Gutenberg EBook of Steam Turbines, by Hubert E. 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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