The Governor

FIG. 47FIG. 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.

FIG. 48FIG. 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 theglands 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 atMandN, 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 theglands were leaking. These circulating valves may be used with any of the arrangements above described.

FIG. 49FIG. 49

On the right-hand end of the main shaft in Fig.34there will be seen a worm gear driving the governor. This is shown on a larger scale atA(Fig.50). At the left of the worm gear is a bevel gear driving the spindleDof the governor, and at the right an eccentric which gives a vibratory motion to the leverF. The crankCupon 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 leverF, 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.

FIG. 50FIG. 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This form of governor has been superseded by an improved type, but so many have been made that it will be well to describe its construction and adjustment.The two ballsW W(Fig.50) are mounted on the ends of bell cranksN, which rest on knife edges. The other end of the bell cranks carry rollers upon which rest a plateP, which serves as a support for the governor springS. They are also attached by links to a yoke and sleeveEwhich acts as a fulcrum for the leverF. The governor is regulated by means of the springSresting on the platePand compressed by a large nutGon the upper end of the governor spindle, which nut turns on a threaded quillJ, held in place by the nutHon the end of the governor spindle and is held tight by the lock-nutK. 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 platePrests upon ball bearings so that by simply bringing pressure to bear upon the hand-wheel, which is a part of the quillJ, 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 yokeEon the pin shown atI, the other end of which is fastened to the piston of a dash-pot so as to dampen the governor against vibration. Under the yokeEwill be noticed a small triggerMwhich 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 sleeveE, carrying with it the collarC, which is spanned bythe leverFupon the shaftH. 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 is shown in section in Fig.51, the main admission being shown atV1at the right, and the secondaryV2at the left of the steam inlet. The pilot valveFreceives a constant reciprocating motion from the eccentric upon the layshaft of the turbine through the leverF(Fig.50). These reciprocations run from 150 to 180 per minute. The space beneath the pistonCis in communication with the large steam chest, where exists the initial pressure through the portA; the admission of steam to the pistonCbeingcontrolled by a needle valveB. The pilot valve connects the portE, leading from the space beneath the piston to an exhaust portI.

FIG. 51FIG. 51

When the pilot valve is closed, the pressures can accumulate beneath the pistonCand 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 fulcrumE(Fig.50) of the leverFwere fixed the admission would be of an equal and fixed duration. But if the governor raises the fulcrumE, the pilot valveF(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 atG(Fig.51). The valve may be opened by hand by means of the leverK, 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 valvesM 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 pistonNand 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 exhaustL, relieving the pressureupon 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 pistonNwith the exhaust may be permanently closed by means of the hand valveQ, 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 chamberWby 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.

This device is mounted on the governor end of the turbine shaft, as shown in Figs.52and53. When the speed reaches a predetermined limit, the plungerA, having its center of gravity slightly displaced from the center of rotation of the shaft, is thrown radially outward and strikes the leverB. It will easily be understood that when the plunger starts outward, the resistance of springCis 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 strucka sharp blow. This releases the tripEon the outside of the governor casing, and so opens the steam valveF, 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.

FIG. 52FIG. 52

FIG. 53FIG. 53

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.

FIG. 54FIG. 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.

FIG. 55FIG. 55

FIG. 56FIG. 56

The oil cooler, shown in Fig.56, is of the counter-current type, the water entering atAand leaving atB, oil entering atC(opening not shown) and leaving atD. The coils are of seamless drawn copper, and attached to the cover by coupling the nut. The water manifoldFis divided into compartments by transverseribs, 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.

FIG. 57FIG. 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 atA(Fig.58), near the top of the blade, and has a groove shown atB(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 groovescut into the rotor drum or the concave surface of the casing, and spacing or packing piecesC(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 atA(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. Thebent-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 itsradial 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.

FIG. 58FIG. 58

FIG. 59FIG. 59

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 thecylinder, 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 caseG(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 theeffect 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, andthat 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 reciprocatingengine, 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.

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 beingremoved 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.

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 actas 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.

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 toclean 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 betaken 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.

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 theHolly 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 drawninto 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 thewater 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.

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.

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 goodqualities 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.

[3]Contributed toPowerby Thomas Franklin.

Thecondensing 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 necessarywith 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.

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