necessary to resort to the jacking gear and jack the engine into a position from which it will start. A vacuum having been generated in the condenser beforehand, the pressure in the receiver acting on the low-pressure piston causes the engine to start promptly, even though the high-pressure crank may be on its center.

Compound slide-valve engines, whether condensing or non-condensing, are stopped by closing the throttle, and, if a reversing engine, throwing the valve gear into mid-position. If the stop is a permanent one, the usual practice of draining the engine, steam chests, and receiver, closing stop-valves, stopping the oil feed, etc. should be followed. If the engine is intended to run in both directions in answer to signals, as in the cases of hoisting, rolling-mill, and marine engines, the operator, after stopping the engine on signal, should immediately open the throttle very slightly, in order to keep the engine warm, and stand by for the next signal. If the engine is fitted with an independent or adjustable cut-off gear, it should be thrown off; that is, set for the greatest cut-off, for the reason that the engine may have stopped in a position in which the cut-off valves in their early cut-off positions would permit little or no steam to enter the cylinders, in which case the engine will not start promptly, and perhaps not at all. While waiting for the signal, the cylinder drain valves should be opened and any water that may be in the cylinders should be blown out. When dry steam blows through the drains, the cylinders are clear of

water.

When the signal to start the engine is received, it is only necessary to throw the valve gear into the go-ahead or backing position, as the signal requires, and to operate the throttle according to the necessities of the case, for which no rule can be laid down beforehand, as the position of the throttle will depend on the load on the engine at the time.

Starting and Stopping Compound Corliss Engine. The operation of starting and stopping a compound Corliss engine is precisely similar to that of starting and stopping a simple Corliss engine. The high-pressure valve gear only is worked by hand in starting, the low-pressure eccentric hook having been hooked on previously. The low-pressure valve gear is worked by hand only while warming up the low-pressure cylinder. The directions given for operating the simple condensing engine apply to the condensing Corliss engine, so far as the treatment of the air pump, circulating pump, and condenser is concerned.

POUNDING OF ENGINES

Faulty Bearings.-Loose journal brasses are the most frequent cause of pounding in engines. The remedy for pounding of this nature is obvious. The engine should be stopped and the brasses set up gradually until the pounding ceases. In the case of shaft journals, they may be set up without stopping the engine, provided the engineer can reach them without danger of being caught in the machinery.

It may so happen that the boxes or brasses are worn down until the edges of the upper half and those of the lower half are in contact and cannot be set up on the journal any farther; they are then said to be brass and brass, or brassbound. In a case of this kind, the journal must be stripped, as it is called, when the cap and brasses are removed from a journal. The edges of the brasses are then chipped or filed off, in order to allow them to be closed in.

It is a most excellent plan in practice to reduce the halves of the brasses so that they will stand off from each other when in place for a distance of to in. and to fill this space with hard sheet-brass liners from No. 20 to No. 22 Birmingham wire gauge in thickness, or even thinner. Should the journal become brass-bound, the cap may be slacked off and a pair of the liners slipped out without the necessity of stripping the journal.

In some instances journal-boxes are fitted with keepers, or chipping pieces, as they are sometimes called. These usually consist of cast-brass liners from toin. in thickness, having ribs or ridges cast on one side, for convenience of chipping and filing. These keepers are sometimes made of hardwood and are capable of being compressed slightly by the pressure exerted upon them during the setting-up process. When the boxes are babbitted, the body of the box is occasionally made of cast iron, in which case iron liners and keepers are used instead of brass ones.

In engines fitted with some types of friction couplings, there is a thrust exerted upon the shaft in the direction of its length. This will necessitate having a thrust bearing, or thrust block, as it is sometimes called. There are a number of types of thrust bearings, but the most common is the collar thrust, which

consists of a series of collars on the shaft that fit in corresponding depressions in the bearing. If these collars do not fit in the depressions rather snugly the shaft will have end play and there probably will be more or less pounding or backlash at every change of load on the engine. This can be remedied only by putting in a new thrust bearing and making a better fit with the shaft collars, unless the rings in the bearing are adjustable, in which case the end play may be taken up by adjusting the rings.

Pounding in Cylinders.-Pounding in the cylinders is frequently caused by water due to condensation or to that carried over from the boilers. This may be a warning that priming is likely to occur in the boilers or has already commenced. If the cylinders are not fitted with automatic relief valves, the drain cocks should be opened as quickly as possible and the throttle closed a little to check the priming.

Another source of pounding in the cylinder is a piston loose on the rod; this will result if the piston-rod nut or key backs off or the riveting becomes loose, permitting the piston to play back and forth on the piston rod. If due to backing off of the nut, the engine should be shut down instantly. There is generally very little room to spare between the piston-rod nut and the cylinder head; therefore, it cannot back off very far before it will strike and break the cylinder head. After the engine is stopped and the main stop-valve is closed, the cylinder head should be taken off and the piston nut set up as tightly as possible. As a measure of safety, a taper split pin should in all cases be fitted through the piston rod behind the nut or a setscrew should be fitted through the nut.

A slack follower plate or junk ring will cause pounding in the cylinder. It seldom happens that all the follower bolts back out at one time, but not infrequently one of them works itself out altogether. This is a very dangerous condition of affairs, especially in a horizontal engine. If the bolts should get end on between the piston and cylinder head, either the piston or the cylinder head is bound to be broken. Therefore, if there is any intimation that a follower bolt is adrift in the cylinder, the engine should be shut down instantly, the cylinder head taken off, the old bolt removed, and one having a tighter fit put in.

Broken packing rings and broken piston springs will cause noise in the cylinder, but it is more of a rattling than a pounding, and the sound will easily be recognized by the practiced ear. There is not so much danger of a breakdown from these causes as may be supposed, from the fact that the broken pieces are confined within the space between the follower plate and the piston flange.

Pounding in the cylinders of old engines is often produced by the striking of the piston against one or the other cylinder heads, due to the wearing away of the connecting-rod brasses. Keying up the brasses from time to time has the effect of lengthening or shortening the connecting-rod, depending on the design, and this change in length destroys the clearance at one end of the cylinder by an equal amount. The remedy is to restore the rod to its original length by placing sheet-metal liners behind the brasses; this obviously will move the piston back or ahead and restore the clearance. A rather rare case of the piston striking the cylinder head is due to the unscrewing of the piston rod from the crosshead, in case it is fastened by a thread and check-nut. To obviate any danger, the check-nut should be tried frequently.

Improper Valve Setting. The primary cause of another source of pounding is the improper setting of the steam valve, or possibly its improper design. In the case of improper setting of the valve, insufficient compression, insufficient lead, cut-off too early, and late release may all cause pounding on the centers.

Reversal of Pressure.-The effect of a reversal of pressure is clearly shown in the accompanying illustration. With the crankpin at a and the engine running in the direction indicated by the arrow, the connectingrod is subjected to a pull, but after the crankpin has passed the dead center c, the connecting-rod is subjected to a push, in which case the rear brass, as shown at b, bears against the crankpin, while in the former case, as shown at a, the front brass bears against the crankpin. By giving a sufficient amount of compression, the lost motion in the pins and journals is transferred gently from one side to the other before the crankpin reaches the dead center. If the compression is insufficient, there will be pounding.

Insufficient Lead.-Insufficient lead causes an engine to pound because the piston has then little or no cushion to impinge on as it approaches the end of its stroke, and it is brought to rest with a jerk. A similar effect will be produced by a late release; the pressure is retained too long on the driving side of the piston. The ideal condition is that the pressures shall be equal on both sides of the piston at a point in its travel just in advance of the opening of the steam port. The position of this point varies with the speed of the piston and other conditions that only the indicator card can reveal.

Pounding at Crosshead.-The crosshead is a source of pounding from various causes, of which the loosening of the piston rod is one of the most common. There are several methods of attaching the piston rod to the crosshead. The rod may pass through the crosshead with a shoulder or a taper, or both, on one side of the crosshead and a nut on the other; or the rod may be secured to the crosshead by a cotter, instead of the nut; or the end of the rod may be threaded and screwed into the crosshead, having a check-nut to hold the rod in place. In the case first mentioned, the nut may work loose, which will cause the crosshead to receive a violent blow, first, by the nut on one side and then by the shoulder or taper on the other, at each change of motion of the piston; the remedy is to set up the nut. A similar effect will be produced if the cotter should work loose and back out. In case the piston rod is screwed into the crosshead and the rod slacks back, the danger is that the piston will strike the rear cylinder head. The check-nut should be closely watched. Pounding at the crosshead may be due to loose wristpin brasses, in which case they should be set up, but not too tightly. In case a crosshead works between parallel guides, pounding may be caused if the crosshead is too loose between the guides, and the crosshead shoes should therefore be set out.

If pounding results from the wearing down of the shoe of a slipper crosshead, a liner should be put between the shoe and the foot of the crosshead or the shoe should be set out by the adjustment provided.

Pounding in Air Pump.-Pounding in the air pump is generally produced by the slamming of the valves, caused by an undue amount of water in the pump, which will usually relieve itself after a few strokes. The pump piston, however, may be loose on the piston rod or the piston rod may be loose in the crosshead. A broken valve may also cause pounding in the air pump, all of which must be repaired as soon as detected.

Pounding in Circulating Pump. In a circulating pump of the reciprocating type, pounding may be caused by admitting too little injection water, and the pounding may be stopped by adjusting the injection valve to admit just the right quantity. It may so happen, however, that the injection water is very cold, and to admit enough of it to stop the pounding in the circulating pump will make the feedwater too cold. To meet this contingency, an air check-valve is often fitted to the circulating pump to admit air into the barrel of the pump as a cushion for the piston; this check-valve may be kept closed when not needed to admit air. A broken valve, a piston loose on its piston rod, and a piston rod loose in the crosshead will all cause pounding in the circulating pump; they should be treated in the same manner as was specified for similar troubles in the air pump.

HOT BEARINGS

Should any of the bearings show an inclination to heat to an uncomfortable point when felt by the hand, the oil feed should be increased. If the bearing continues to get hotter, some flake graphite should be mixed with the oil and the mixture should be fed into the bearing through the oil holes, between the brasses, or wherever else it can be forced in.

If, after trying the remedies just mentioned, the bearing continues to grow hotter, to the extent, for instance, of scorching the hand or burning the oil, it indicates that the brasses have been expanded by the heat and that they are gripping the journal harder and harder the hotter they get. At this stage, if the engine is not stopped or if the heating is not checked, the condition of the bearing will continue to grow worse, and may become so bad as to slow down and eventually stop the engine by excessive friction. By this time the brasses and journal will be badly cut and in bad condition generally, and the engine must be laid up for repairs.

After the simple remedies previously given have been tried and failed to produce the desired results, the engine should be stopped and the cap or key of the hot bearing should be slacked back and the engine allowed to stand until the bearing has cooled off. If necessary, the cooling may be hastened by pouring cold water on the bearing, though this is objectionable, as it may

cause the brasses to warp or crack. Putting water on a very hot bearing should be resorted to only in an emergency, that is, when an engine must be kept running. Water may be used on a moderately hot bearing without doing very much harm. It is quite common in practice, when sprinklers are fitted to an engine, to run a light spray of water on the crankpins when they show a tendency to heat, with very beneficial results.

Dangerous Heating. Should a bearing become so hot as to scorch the hand or to burn the oil before it is discovered it is imperative that the engine should be stopped, at least long enough to loosen up the brasses, even though it is necessary to start up again immediately; otherwise the brasses will be damaged beyond repair and deep grooves will be cut into the journals. If the brasses are babbitted, the white metal will melt out of the bearing at this stage. engine will then be disabled, and if there is not a spare set of brasses on hand, it will be inoperative until the old brasses are rebabbitted or until a new set is made and fitted.

The

If it is absolutely necessary in an emergency to keep the engine running while a bearing is very hot, the engineer must exercise his best judgment as to how he shall proceed. After slacking off the brasses, about the best he can do is deluge the inside of the bearing with a mixture of oil and graphite, sulphur, soapstone, etc., and the outside with cold water from buckets, sprinklers, or hose, taking the chances of ruining the brasses and cutting the journal.

Refitting Cut Bearing.-The wearing surfaces of the brasses and journal must be smoothed off as well as circumstances will permit; but if the grooves are very deeply cut, it will be useless to attempt to work them out entirely, and if the brasses are very much warped or badly cracked, it will be best to put in spare ones, if any are on hand. If not, the old ones must be refitted and used until a new set can be procured. As for the journal, it is permanently damaged. Temporary repairs can be made by smoothing down the journal and brasses; but at the first opportunity the journal should be turned in a lathe and the brasses properly refitted or replaced with new ones.

Newly Fitted Bearings. The bearings of new engines are particularly liable to heat, as the wearing surfaces of the brasses and journal have just been machined and hence are comparatively rough. The conditions just mentioned also exist with new brasses and the journals of an old engine. If a new engine, or one with new brasses is run moderately, in regard to both speed and load, and with rather loose brasses, there will be little danger of hot bearings, provided proper attention is given to adjustment and lubrication. This is what is familiarly termed wearing down the bearings.

Faulty Brasses.-When the brasses of an engine bearing are set up too tight, heating is inevitable. Often, an attempt is made to stop a pound in an engine by setting up the brasses when the thump should be stopped in some other way. The brasses should be slacked off as soon as possible. As a matter of fact, hot bearings should never occur from this cause.

Bearings may heat because the brasses are too loose. The heating is caused by the hammering of the journal against the brasses when the crankpin is passing the dead centers. The derangement is easily remedied, however, by setting up the cap nuts or the key. Most engineers have their own views regarding the setting up of bearings. One method is to set up the cap nuts or key nearly solid and then slack them back half way; if the brasses are still too loose, they are set up again and slacked back less than before, repeating this operation until there is neither thumping nor heating.

Another method of setting up journal brasses is to fill up the spaces between the brasses with thin metal liners, from No. 18 to No. 22 Birmingham wire gauge in thickness, and a few paper liners for fine adjustment. Enough of these should be put in to cause the brasses to set rather loosely on the journal when the cap nuts or keys are set up solid. The engine should be run for a while in that condition; then a pair of the liners should be removed and the brasses set up solid again. This operation should be repeated until there is neither thumping nor heating. It may require a week or more, and with a large engine longer, to reach the desired point. If this system is carefully carried out, there will be very little danger of heating. In removing the liners, great care should be exercised not to disturb the brasses any more than is absolutely necessary.

Warped and cracked brasses will cause heating, because they do not bear evenly on the journal, and hence the friction is not distributed evenly over the entire surface. If the distortion is not too great, the brasses may be refitted to the journal by chipping, filing, and scraping; but if they are twisted so much that they cannot be refitted, nothing will do but new brasses.

Brasses and journals that have been hot enough to be cut and grooved are liable to heat up again any time on account of the roughness of the wearing surfaces. As long as the grooves in the journal are parallel and match the grooves in the brasses, the friction is not greatly increased; but if a smooth journal is placed between brasses that are grooved and pressure is applied, the journal crushes the grooves in the brasses and becomes brazed or coated with brass, and then heating results. The way to prevent heating from this cause is to work the grooves out of the journal and brasses by filing and scraping as soon as possible after they occur.

Faulty workmanship is a common cause of the heating of crankpins, wristpins, and bearings. The brasses in that case do not bear fairly and squarely, even though they appear all right to the eye. A crankpin brass must fit squarely on the end of the connecting-rod and the rod itself must be square. If the key, when driven, forces the brasses to one side or the other and twists the strap on the rod, it will draw the brasses slantwise on the pin and make them bear harder on one side than on the other, thus reducing the area of the bearing surfaces. The same is true of the shaft bearings. If the brasses do not bed fairly on the bottom of the pillow-block casting or do not go down evenly, without springing in any way, heating will result

If the brasses are too long and bear against the collars of the journal when cold, they will most surely heat after the engine has been running a while. It is hardly possible to run bearings stone cold. They will warm up a little and the brasses will be expanded thereby, which will cause them to bear still harder against the collars. This, in turn, will induce greater friction and more expansion of the brasses. The evil may be obviated by chipping or filing a little off each end of the brasses until they cease to bear against the collars while running. A little side play is a good thing because it also promotes a better distribution of the oil and prevents the journal and brasses from wearing into concentric parallel grooves.

Edges of Brasses Pinching Journal.-Brasses, when first heated by abnormal friction, tend to expand along the surface in contact with the journal; this would open the brass and make the bore of larger diameter were it not prevented by the cooler part near the outside and by the bedplate itself. If the brass has become hot quickly and excessively, the resistance to expansion produces a permanent set on the layers of metal near the journal, so that on cooling, the brass closes and grips the journal. This is why some bearings always run a trifle warm and will not work cool. A continuance of heating and cooling will set up a bending action at the middle of the brass, which must eventually end in cracking it. Heating produced in this way may be prevented by chipping off the brasses at their edges parallel to the journal, as shown at a in the accompanying illustration, in which b is a section of the journal and c and d represent the top and bottom_brasses, respectively.

Hot Bearings Due to Faulty Oiling. It does not take long for a bearing to get very hot if it is deprived of oil. The two principal causes of dry bearings are an oil cup that has stopped feeding, either by

reason of being empty or by being clogged up from dirt in the oil, and oil holes and oil grooves stopped up with dirt and gum.

The effect produced upon a bearing by an insufficient oil supply is similar to that of no oil, but in a less degree. Of course, it will take longer for a bearing to heat with insufficient oil than with none at all, and the engineer has more time in which to discover and remedy the difficulty.

Oils that contain dirt and grit are prolific sources of hot bearings. There is a great deal of dirt in lubricating oils of the average quality; therefore, all oil should be strained through a cloth or filtered, no matter how clear it looks. All oil cups, oil cans, and oil tubes and channels should be cleaned out frequently. Oil may be removed from the cups by means of an oil syringe, and all oil removed from the cups and cans should be strained or filtered before being used.

There are on the market many lubricating oils whose quality cannot be definitely decided on without an actual trial, and it is difficult to avoid getting a bad lot of oil sometimes. About the only safe way to meet this trouble is to pay a fair price to a reputable dealer for oil that is known to be of good quality, unless the purchaser is expert in judging oils or is able to pay a competent chemist to test them.