nal. He found that the car resistance in pounds per ton (2,240 pounds) of weight of train on straight and level track in good condition was for empty cars 14 pounds in starting, while for a loaded car it was equal to 18 pounds per ton in starting. When a speed of 10 miles per hour was attained, however, the resistance due to axle, tire and flange friction for the empty car was found to be 6 pounds per ton, while that of the loaded car was but 4 pounds per ton. The same relation holding good up to a speed of 30 miles per hour. The total resistance toward movement of the car increased, however, for an empty car with the increase in speed, so that at 30 miles per hour, the empty car showed a resistance of 14 pounds per ton, while the loaded car showed a resistance of but 11 pounds per ton, the additional resistance being due to oscillation and concussion

According

and the resistance of the air. to Professor Thurston, the coefficient of friction between a steel journal and a bronze bearing lubricated with sperm oil increases with the increase of pressure per square inch until the speed of the journal has reached about 1,000 feet per minute, after which it begins to reduce. From a number of tests that have been conducted recently, however, it would appear that, as per previous statement, the friction does not increase in proportion to the increase in load, and it is on this hypothesis only that we can explain the difference in resistance per ton of the 20-ton and 65-ton cars. The following is a table compiled by Edward C. Smith, of the University of Illinois Engineering Experiment Station, covering freight train resistance, and its relation to car weight, which gives the various resistances requested:

10.

8.2 7.3 6.5

5.2

4.7 4.3 4.0 3.7

11

8.3 7.4 6.6

12

8.4 7.5

6.7

6.0

13

8.6 7.6

• 6.8

6.1

14

8.7 7.8

9.0 8.0

26

10.5 9.4

8.4

7.5

6.8

6.1

5.6

6.6 6.0 5.5 5.1

The operation of the air signal is as follows: Assuming the air signal system is charged to 45 pounds, if a car discharge valve is opened for about a second, the proper interval, the consequent reduction in pressure will travel to the engine and, because of the more free opening to the upper than to the lower chamber in the signal valve, will reduce the pressure above the diaphragm below that beneath it. This will cause the diaphragm 12 to raise the stem 10, open the passage to the signal whistle and cause a blast at the latter.

The feed into the air signal system is purposely made slow, so much so that a considerable leak will prevent charging and, hence, operation. Not only is this necessary to insure accurate operation, particularly with long trains, but it has the great virtue that a bad leak developing when running, as from a burst signal hose, will not stop the train, as even a 9-inch pump in fair condition can supply it and the ordinary leakage from the air brake system.

Simple as the signal valve is, the accuracy of adjustment required for the

This same reduction causes the signal reducing valve to increase the feed into the signal line. As this increase in pressure enters chamber A at the top of the diaphragm and as the opening to the whistle is tending to reduce the pressure in chamber B below the diaphragm the higher pressure above forces it downward, seating its valve and ending the whistle blast.

As the car discharge valve should be left closed for two seconds or more after each opening of it, this allows the pressure to become equalized throughout the air signal system and insures correct operation even though the pressure may not be fully restored to 45 pounds between discharges.

best operation results in the manufacturers offering to repair without charge worn valves sent to them.

The proper location for the signal valve is the right, back corner of the cab, near the roof. The object is to protect it against extremes of heat or cold. In good weather the engineer keeps it reasonably cool by opening at least the side window, and in cold weather he prevents it from collecting frost, and thereby becoming inoperative, by closing the cab for his own comfort. This location was selected so he would not forget to care for the signal valve.

In this position of the signal valve, a short pipe bent U-shaped, omitting the ells shown in the illustration, is all that

is needed for the signal whistle, but the latter should be so located as to be shielded by the signal valve from strong wind, as the latter would weaken or prevent the whistle sound.

Ordinarily there are but two faults ever found with the whistle itself. One is such an accumulation of dirt in the narrow groove around the bowl of the whistle as to interfere with the air discharge. The other is wrong adjustment of the bel or upper portion. It is secured on a stem and can be raised or lowered by changing the position of the nut inside at the top of the bell and exposed by removing the latter.

If properly adjusted for the regular pressure and well secured it will remain so, but uninformed persons have been known to alter this adjustment when the defect sought was elsewhere. Before altering the whistle adjustment see whether the pressure carried is right. If the whistle is taken apart to clean the bowl, be careful not to change the adjustment of the bell.

823. Pump Stops.-"If a pump merely stops on a stormy winter day, where would you first look for the trouble?"C. F. R.

Answer.-Usually the first indication the engineer would observe of something wrong would be insufficient pressures shown by the air gauge. His next duty

would be to see whether the air pump was working properly. If stopped or working very slow, even under weather conditions as mentioned, first open the pump drain cocks so as to judge whether or not it is getting a good supply of steam. If it is and there is reason to believe the pump air discharge pipe is "frozen up," filled with an accumulation of frost, it can be determined definitely by slacking the union at the pump end of this pipe, thereby making a leak. (This is not advised with a soft gasket joint in the union unless a new gasket can be applied quickly if needed.) the pump starts freely or increases in speed with the leak made, stop the leak and heat the portion of the discharge pipe where the frost is liable to be. This will be near the main reservoir end and particularly a sharp turn in this portion and where it is most exposed to the cold when the engine is running. A shovelfull of coals or a torch of oil-soaked

If

waste or rags on a packing hook will soon loosen the frost.

If the air blows strong when the leak is made and the pump does not start it shows that the discharge pipe is not frozen up and that the trouble is with the pump or the governor.

Most roads now follow more or less the recommendations of the Air Brake Association to use a long pump discharge pipe and so arranged as to cool the air. On different roads this will vary from 25 to nearly 50 feet. At least two main reservoirs are recommended and about 50 feet of connecting pipe between them, also in a cool location. Each of these pipes should drain in the direction that the air flows, commencing within about ten feet of the inflow end, where the air enters it.

The object sought is to cool the air (it is raised to a high temperature by compression in the pump) and thereby deposit all surplus moisture. If this is not accomplished, more or less moisture will reach the brake pipe, which is liable to stop the latter with frost in freezing weather and is always detrimental to triple valves and distributing valves.

How much moisture will reach the brake pipe depends mainly on (1) how moist the air is on entering the pump (steam leaks near the suction opening load it with moisture); (2) how thoroughly the air is cooled before it passes from the last main reservoir to the brake valve; and the quantity of air used by the train.

Avoid steam leaks near the pump suction opening. Locating the latter in the cab and near the roof is bad, as all steam from boiler head leaks goes to this point promptly. In very cold weather the cab is kept as well closed as practicable, thus bottling up the steam leaks and thereby greatly increasing the liability of the discharge pipe freezing up with suction opening in the cab.

In very cold weather the air is naturally dry and if it can be kept so until it has entered the pump there will be little liability of a frozen discharge pipe if the latter is put up right. But better a frozen discharge pipe than a frozen brake pipe. The air gauge shows the former, by the gradually falling pressures, and the brakes can be applied on the entire train, but the engineer has no such warning with a frozen brake pipe and cannot apply the air brakes back of the point closed by frost.

824. Bleeding Brake With Empty Brake Pipe. "If a car auxiliary reservoir and brake pipe were charged to 70 pounds, the angle cock then opened and left so, no more air being admitted to the brake pipe, and you were to bleed this brake, what path would the air use in getting out of the brake cylinder?"-N. V. C.

Answer. The triple valve would be in emergency position, thereby maintaining a connection between the auxiliary reservoir and the brake cylinder. Hence, on opening the release valve or "bleeder" on the auxiliary reservoir the air in the brake cylinder would flow back into the auxiliary reservoir, passing through the small port in the end of the triple valve slide valve, and thence through the release valve to the atmosphere.

This would continue until the pressure in the auxiliary reservoir and brake cylinder was low enough to permit the graduating spring in the triple valve to move the piston and the slide valve in the latter to lap position. Owing to the large area of the triple valve main piston (9 square inches) against which the auxiliary reservoir pressure acts and to the resistance of the slide valve, the pressure will be so low by the time this action cuts off communication between the auxiliary reservoir and the brake cylinder that there will be no effective holding power remaining on the brake. Usually the brake cylinder piston will be back far enough for the leakage groove to discharge the remaining pressure. Unless the triple slide valve spring were unnecessarily strong the slide valve would raise slightly as the auxiliary reservoir was finally emptied of air and aid in discharging the last of the brake cylinder pressure. If this spring were strong the pressure in the auxiliary reservoir and the brake cylinder would be lower before the graduating spring could move the slide valve back toward lap position. The brake cylinder release spring moves its piston back as the pressure gets low.

825. Why Quick Service With K Triple Valve. -"As the quick service feature of the K triple valve merely increases the rate of brake pipe reduction by discharging air from the brake pipe into the brake cylinder in service reductions, why could not the same results be obtained more simply by enlarging the service exhaust port in the brake valve? Is it because it would be more liable to cause undesired quick action?"-A. D. T.

Answer. Answering the last question first, the service exhaust port could be materially increased in size without in

creasing undesired quick action. In fact, before the K triple valve was perfected a brake valve with this feature was de

signed and thoroughly tested out in service. It caused no undesired quick action, but one day when the train of about 50 cars had just been well started a stop signal was given, the engineer shut off and made a moderate service reduction. It will be appreciated that there was nothing very unusual in this, but the result was seven pretty thoroughly wrecked cars. To do as the engineer did is not good practice at any time and it is occasionally the cause of considerable damage to draft rigging, but not to the extent just related. Why?

The reason is because the more rapid discharge at the brake valve increased the rate of reduction toward the head end of the train but could not do so to the rear because of the friction of the air on the long brake pipe. The slack of the train had been drawn out heavily, the coupler springs compressed (they are compressed when the couplers are pulled on as well as when pushed on). Shutting off and making the service reduction was the usual deliberate action, not hurried, and as soon as the engine stopped pulling the coupler springs started the slack in from both ends of the train. Then, with the more rapid service reduction on the head cars and the slow speed, where the holding power of the brakes is high, the head end stopped suddenly, "anchored," bunching the slack solidly on the forward portion of the train as it stopped.

Bear in mind also that while the coupler springs were helping the brakes to stop the forward end of the train, by pulling it toward the rear, they were pulling the rear end of the train forward and at the same time closing up its slack. The result was a small sized collision of two well bunched portions of the train and without having been uncoupled. The standard size of service exhaust opening has the same tendency, but cannot reduce the head end of the brake pipe so much faster than the rear end. Hence, the results under similar circumstances, while at times bad enough, would not be near as serious.

If the slack is in when a reduction is begun there is no noticeable effect; if it was out light just before it will be run in from the head to the rear end largely one car at a time and there is no liability of serious draft rigging damage,