117.

Answers by W. G. Wallace.

Friction."Upon what does the amount of friction depend?”—A. T. M. Answer.-Friction is the resistance that a body meets with from the surface on which it moves, and depends on the pressure between the surfaces and the condition of same. A body moving over a smooth surface will produce less friction than when moving over a rough surface, and is greater between soft bodies than hard ones. It is proportional to the perpendicular pressure between two faces in contact.

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118. Oil and Frictional Surfaces.-"What is the effect of introducing oil between frictional surfaces?"-A. T. M.

Answer. Reduction of friction, less wear on the bearings, and separating the metals of same by placing a film of oil between them. If we had a heavy box to slide on a platform and could not move it, the reason would be that the friction was greater than the power. If we had a layer of grease or a film of oil between the surfaces in contact it could be moved more easily. This would be sliding friction. Then if we put rollers under it we could roll it easier than we could slide it. This would be rolling friction, and the film of oil introduced between two bearings acts as rollers in reducing the friction and keeping the metals apart.

119. Abuse of Engines.-"What would you consider abuse of engines?"—A. T. M.

Answer-Slipping engine when taking her from the roundhouse track without opening the cylinder cocks to let the water out of the cylinders; slipping her at any time and catching her on sand at any time without closing the throttle; reversing engine with brake set, sliding drivers and flattening tires; poor pumping, knocking the steam pressure down by too much injector, and pulling out of stations without having fire in proper condition; working engine harder than necessary to handle train and make time; working water and wet steam through valves and cylinders; imperfect lubrication; firing engine without getting coal on forward section of grates, causing flues to leak; failure to tighten a nut or drive

a key where needed, and not reporting necessary work on arrival at terminals, all go toward the abuse of an engine.

tion of the eccentrics on the shaft or axle are directly opposite to the position that they would be in if this was an outside admission valve. Instead of being advanced toward the pin the amount of lap and lead, they are advanced away from the pin. The internal or external admission valves make this change of position of the eccentrics necessary with an indirect rocker. This illustration is a view of an indirect motion or rocker, because the valve is traveling in one direction and the eccentric is traveling in the

opposite direction. Fig. 2 shows the same kind of a valve with inside admission, but with a direct motion or rocker, and the eccentric and valve both move in the same direction. In this illustration the eccentrics are placed on the shaft in the same position as if you had an indirect rocker with an outside admission valve.

The front steam port must be opened to admit steam to the cylinder in both illustrations. If your engine is put up

as shown in Fig. 2 you have a directmotion engine. Fig. 3 shows an indirect rocker on the left and a direct rocker on the right, or a rocker with a link arm and the valve arm opposite each other is a direct rocker.

122. Troublesome Boiler Checks. - "I am firing an eight-wheel wagon-top boiler engine equipped with No. 8 Monitor injectors on both sides. The

boiler checks are in the barrel of the boiler and set about level with the center of same. The injectors are on a level with the top of the tank and they work in good shape until the tank is one-half empty and less. Then every time the injector on either side is shut off the boiler checks stick up, and they give no trouble at any other time when the tank is over half full of water. Both checks have been ground in, examined and pronounced all right and give no sign of leaking when injectors are not in use. What is the trouble?"-H. E. B.

Answer. From the description given of the action of the checks, it is the opinion of experts that the trouble is from sediment deposited on the valve and interior of the cage and passage to boiler through check, and that the check valve may be fitted too close to allow any deposit without interfering with the free action of the check. The height of water in the tank would in no way influence the boiler check if in proper condition. Possibly the valve and seat may be battered sufficiently to cause too tight a fit for free action of the valve. This case would require a personal examination in order to render a definite conclusion, and we would recommend that the check be made sufficiently loose so that the valve would find its seat readily at all times when the injector was shut off.

123. Injector Worked by Air Pressure.-"Can an injector be worked on a boiler with air pressure on it instead of steam? If not, why not? I have consulted several

Answer. No, it can not. The injector is an instrument that will force water into a boiler against a pressure equal to that of the steam that is used in its operation. Steam in forcing water through the injector and into a boiler gives up heat and imparts a velocity to the water, and starts it with a momentum sufficient to overcome a pressure even higher than the original pressure of steam. A great deal of the velocity of the steam is given up to the water, and gives the water sufficient energy to open the check valve and enter the boiler. As the steam condenses in imparting its heat and velocity to the water the pipe is solid full of water. When the water will not condense the steam or is too high a temperature (too hot) the injector will not work. Therefore, the reason that the injector will not work with air pressure is that the mixture of air and water would make bubbles and it would not be a solid body of water to absorb the velocity or mix with the air, as you could not have air and water occupying the same space at the same time. Our experience has been when reversing an engine and opening the throttle to prevent striking the rear end of a preceding train that the injector always broke on account of the air mixing with the steam.

124. Per Cent. of Heat Used.-"Will you kindly give me the per cent. of heat used and the per cent. of heat that escapes from the stack of a locomotive while working?"-S. W. D.

Answer.-In order to make this clear we will have to take an example and work out the answer. Conditions vary so much that the answer will only be approximately correct for this specific case.

We will assume that we have an engine with 22x27-inch cylinders; driving wheels 56 inches in diameter, with a boiler pressure of 175 pounds, and running at a speed of 12 miles per hour. Allowing a mean effective pressure in the cylinders of 78 per cent. of the boiler pressure we would obtain a tractive power of 33,000 pounds, or the locomotive would develop one horse-power per foot run, and at 12 miles per hour it would be equal to 1,056 horse-power. If the engine run 15 miles per ton of coal at 12 miles per hour she would burn twenty-six and six-tenths (26.6) pounds of coal per minute. Now all the energy that we are to get from the engine is stored in the coal, and is called heat units. The mechanical equiv

thermal unit (B. T. U.), when changed to work is equal to 778 foot-pounds of work. Then, figuring that one pound of coal contains 11,660 B. T. U., or heat units, we would have stored in twenty-six and six-tenths (26.6) pounds of coal 7,320 horse-power if all the heat units could be converted into work. But as they can not we will have the difference between the energy taken from or liberated from the coal by combustion and the energy delivered to the drawbar to overcome the train resistance, which would be 7,320 and 1,056 horse-power, respectively, or about fourteen and four-tenths (14.4) per cent. of the heat in the coal used.

125. Temperature.-"How was the degree of temperature first found and determined."-W. H. M.

Answer.-Dr. Joule, of England, found by tests and a series of careful experiments that a British thermal heat unit was equal to 778 foot-pounds of work. A British thermal heat unit is a quantity of heat that will raise the temperature of one pound of water one degree, or from 62 degrees to 63 degrees Fahrenheit. The Fahrenheit thermometer is the kind generally used in this country, and is an instrument used for measuring temperature. It consists of a thin glass tube, at one end of which there is a bulb filled

with mercury. Upon being heated, the mercury expands in proportion to its temperature. The Fahrenheit thermometer is graduated to show the degrees of heat, as follows:

Take the glass tube and surround it with melting ice at a temperature of 32° and mark the tube at the height of the mercury. Then surround the tube with a temperature of boiling water at sea level which is 212°, the mercury expanding in the tube and rising higher than when it was at the temperature of melting ice. Now mark the tube where the mercury stands at the temperature of boiling water and divide the distance into 180 parts, called degrees, as shown by the height of the mercury in the tube on a Fahrenheit thermometer.

126. Broken Piston Valve.-"I wish to ask the Magazine how to get at it to bring in a piston-valve engine with a piston valve on one side broken and nothing to do it with, only the tool equipment that is necessary to get an engine over the road?"-J. W. B.

Answer. First get the good side on the eighth or quarter so you can start engine

92-inch, was run very fast, but did not get hot. The weather was very cold. It took over an hour to get 60 pounds pressure, with which the first stop was made. The train crew claimed the brakes were well inspected at the terminal and that there were no leaks, but I noticed at this stop that the brakes took hold pretty severe for the reduction I made.

"At the end of the trip I looked for leaks on the engine, but could find none; so reported the pump air cylinder examined. The machinist said he found both discharge ports choked with gum and that the lower one had only a small hole through it. Coming back we had about fifty cars, but had no trouble to keep up full pressure. What do you think the trouble was?"-T. S.

Answer-As the pump ran fast and

did not overheat, it is evident that the discharge ports were not sufficiently choked up to materially affect its operation. When discharge ports are so small as to cause trouble the pump will overheat and will not run very fast, unless the air-piston-packing rings are very leaky. That this pump did not overheat, ran fast and maintained full pressure with a much longer train on the return trip is sufficient evidence that little, if any, of the fault was with it. On the other hand, the severe holding of the brakes with the first train was apparently due to train-pipe leakage added to the reduction made with the brake valve.

Train men and inspectors are not so anxious to look for leaks on a cold night as to ever warrant accusing them of making a train so tight as to cause the pump to freeze up from running slow. Watch both gauge hands when applying the brakes on a train that is difficult to "pump up." If the red hand moves up about as fast as usual with such a pump speed, and if the black hand keeps reducing below the pressure left after the reduction, the fault is neither in the pump, the main reservoir or any of the connections to the latter. But before charging it to the train be sure it is not train-pipe leakage on the engine or the tender. However, any fault on the engine or tender should be noticed at the roundhouse, or, at the latest, between there and where the train is coupled to.

178. What Ailed the Pump?-"A new pump was put on an engine here. The engine went out on a local run and when about seventeen miles out of the division point the pump stopped and the engineer tried every way possible to start it. I was sent to the terminal where the engine laid up overnight, and I examined the air end first, but found everything all right. Then I examined the steam end, and

everything there was O. K. Went into the governor and found it in good order. Steam entered the cylinder all right. Where do you suppose I found the trouble?"-K. O. P.

Answer. The circumstances as ex

plained seem to indicate a stoppage in the exhaust pipe. In the days of air

brakes on only the engine and tender in freight service it has been claimed that with the pump shut off for several trips sufficient cinders accumulated and packed in the end of the pump exhaust pipe to prevent the pump from running when steam was turned on.

In the case you mention the writer can suggest only the possibility of some obstruction having entered the pipe before the pump was connected and was later driven along by the steam until it lodged.

179. Should Driver Brake Leverage Vary With Diameter of Wheels?-"Will you kindly explain through the columns of the technical department why the size of the wheel is not taken into consideration when figuring brake leverage? For example, suping wheels, equipped with a driver brake, pose we have an engine with 60-inch driv

the leverage of which is such that when a full application is made the adhesion between the wheels and the rails is just sufficient to prevent the wheels from sliding. Now, without changing the weight of the engine or the length of the brake levers, let us change the driving wheels, replacing the 60-inch with 80-inch wheels.

"Next, let us consult the accompanying illustration. It is plain to be seen

that with the 60-inch wheels the brake shoes have 30 inches of leverage, while with the 80-inch wheels the leverage is 40 inches. Now, as the adhesion between the wheels and the rails is the same in both cases, should not the 10-inch inslide? Or, in other words, should not the creased leverage cause the wheels to

size of the wheels be taken into consideration when figuring brake leverage? In my judgment it should be, but I have never noticed in any rules of brake leverwould be very thankful for an explanaage where it was considered; therefore,

tion."-T. E. L.

Answer. By adding to the illustration, as has been done, the figures indicating the distance from the rails to the center of the axles, the reason why the large wheels will be no easier to slide than will the smaller ones can readily be seen.

In braking there are two opposing forces, the friction between the brake shoes and the wheels, which resists turning or rotation, and the friction or adhesion between the wheels and the rails, which, when the engine is in motion or is standing on a steep grade, tends to cause