III. ALLIS-CHALMERS COMPANY STEAM TURBINE

FIG. 23FIG. 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 possibleto 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.

FIG. 24FIG. 24

InFig.25may 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.

FIG. 25FIG. 25

Fig.26is a longitudinal cross-section cut of rotor and both lower and upper casing. Referring to Fig.26the steam comes in from the steam-pipe atCand passes through the main throttle or regulating valveD, which is a balanced valve operated by the governor. Steam enters the cylinder through the passageE.

Turning in the direction of the bearingA, it passes through alternate stationary and revolving rows ofblades, finally emerging atFand going out by way ofGto the condenser or to atmosphere.H,J, andKrepresent three stages of blading.L,M, andZare the balance pistons which counterbalance the thrust on the stagesH,J, andK.OandQare 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.

FIG. 26FIG. 26

Rindicates a small adjustable collar placed inside the housing of the main bearingBto 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.

AtSandTare glands which provide a water seal against the inleakage of air and the outleakage of steam.Urepresents the flexible coupling to the generator.Vis the overload or by-pass valve used for admitting steam to intermediate stage of the turbine.Wis the supplementary cylinder to contain the low-pressure balance piston.XandYare 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, andZ. 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,LandM, 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 cylinderW. 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 pistonM, 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.25between 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 pistonZhas, 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.

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 atAin 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.31and atBin Fig.27. Fig.31shows the cylinder blading separate, and Fig.27shows both with the shrouding. In these, holes are punched to receivethe projections on the tips of the blades, which are rivetted over pneumatically.

FIG. 27FIG. 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 atCin Fig.27. Each keypiece, when driven in place, is upset into an undercut groove, indicated byDin 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.

FIG. 28FIG. 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.

FIG. 29FIG. 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 theblades 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.

FIG. 30FIG. 30

The blading is made up and inserted in half rings, and Fig.30shows two rings of different sizes ready to be put in place. Fig.31shows a number of rows of blading inserted in the cylinder of an Allis-Chalmers steam turbine, and Fig.32gives view of blading in the same turbine after nearly three years' running.

FIG. 31FIG. 31

FIG. 32FIG. 32

Next in importance to the difference in blading and balance piston construction, is the governing mechanismused 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 anoil 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 importanceis 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 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.33shows 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.

FIG. 33FIG. 33

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.

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 revolvingvery 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 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 oilflowing 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 turbineis 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.

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.

Whilethe 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 ofwhich 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.

FIG. 34FIG. 34

Fig.34is a sectional view of the standard Westinghouse-Parsons single-flow turbine. A photograph of the rotorR R Ris reproduced in Fig.35, while in Fig.36a 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 atA(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 pressurePto the slightly lower pressureP1, 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 pressureP1toP2and 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.

FIG. 35FIG. 35

FIG. 36FIG. 36

FIG. 37FIG. 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.

FIG. 38FIG. 38

In the passageA(Fig.34) exists the initial pressure; in the passageBthe pressure after the steam has passed the first section or diameter of the rotor; in the passageCafter 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 Prevolving with the shaft and exposing in the annular spacesB1andC1the same areasas those of the blade sections which they are designed to balance. The same pressure is maintained inB1as inB, and inC1as inCby connecting them with equalizing pipesE E. The third equalizing pipeconnects 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 fromA,B1andC1to 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.

FIG. 39FIG. 39

The axial adjustment is controlled by the device shown atTin Fig.34and on a larger scale in Fig.40. The thrust bearing consists of two parts,T1T2. Each consists of a cast-iron body in which are placed brass collars. These collars fit into groovesC, turned in the shaft as shown. The halves of the block are brought into position by means of screwsS1S2acting on leversL1L2and 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.

FIG. 40FIG. 40

The upper screwS2is set so that when the rotorexerts 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 screwS1is 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 latchL3. To do this the pinP4must 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 tocease. 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 theear 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 thrustbearingitself, 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.

The bearings which support the rotor are shown atF Fin Fig.34and in detail in Fig.41. The bearing proper consists of a brass tubeBwith proper oil grooves. It has a dowel armLwhich 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 nutF, and this nut, in turn, is held by the small set-screwG. The bearing with the surrounding tubes is placed inside of the cast-iron shellA, which rests in the bearing pedestal on the block and linerH. The packing ringMprevents 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.

FIG. 41FIG. 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 obtainedon 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 rotoris 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.42aand42b. These bearings are self-alining and have the same liner adjustment as the concentric-sleeve bearings just described. Oil is supplied through a holeDin the lower liner pad, and is carried to the oil grooveFthrough the tubesE 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.

FIG. 42AFIG. 42A

FIG. 42BFIG. 42B

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 packingW 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 atA(Fig.44), pass over the projecting ringsB, the function of which is to throw off any water which may be creeping along the shaft by centrifugal force into the surrounding spaceC, whence it escapes by the drip pipeD, hence over the five rings of the labyrinth packingEand thence over the top of the revolving blade wheel, it being apparent from Fig.43that 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 thepipe 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 impossiblefor 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 waterto leak outward through the labyrinth packing either into the vacuum or the atmosphere.

FIG. 43FIG. 43

FIG. 44FIG. 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.

FIG. 45FIG. 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 theboilers 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.

FIG. 46FIG. 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 bedescribed in detail later, the coils may be attached to either of the above arrangements as shown in Fig.47.

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