Q. To what does this point?

A. To the possibility-indeed, the necessity-of greater brake cylinder and brake shoe pressure with high speeds; provided this increased pressure can be reduced down as the speed decreases.

Q. How is this reduction effected?

A. By the automatic reducing valve.

Q. What effect does it have on a bridge to apply brakes when the train is thereon?

A. There is a force produced which tends to push the rails in the direction the train is running.

Q. What effect does it have on a bridge to apply brakes before reaching it, and to hold them on while the train is passing over the bridge?

A. Same as preceding answer.

Q. Will a cam driver-brake set the brake harder with a long or short piston travel, provided the air pressure is the same in the brake cylinder in both cases?

A. The brake will set tighter with the longer piston travel. The cam screws are brought more nearly horizontal where the greatest power of the brake is obtained. In other words, with the short travel the cams stand higher, and have a downward thrust as well as one towards the wheel center.

Q. Why is it that an engine air gage will show 70 pounds brake pipe and 90 pounds main reservoir with engine when not coupled to any cars, but as soon as coupled up to the train, the brake pipe hand may drop 5 pounds or more? When the engine is cut off afterward, the hands stand all right again. It is a D-5 (1892 model) brake valve.

A. As the brake pipe pressure approaches 70, the supply valve begins to close making a smaller opening through the brake valve to the brake pipe. If the brake pipe is tight, the supply valve will finally close and the brake pipe pointer on the gage will register full brake

pipe pressure. However, should the brake pipe leak, the supply valve cannot close, but must remain open and feed the leaks. If the leaks are heavy the valve will stay open, and the gage register short of full brake pipe pressure, in proportion to the leakage.

Q. What are the various causes for wheel sliding, which particularly concern the train and engine men? A. (1) Too high (over 70 pounds) brake pipe pressure. (2) Hand brake, especially if used with air brake. (3) Sticking brakes (triples, with poorly fitting packing rings). (4) Leakage by rubber seat of emergency valve. (5) Plugged up exhaust port of retaining valve in either of its positions. (6) Heavy brake applications, especially with empty cars or on a slippery rail. (7) Too short piston travel. (8) Unequal distribution of brake power where rigging has a short equalizing lever and same strikes, under brake application, on rod jaw by reason of slack being taken up too much on one end of the car. (9) Brake shoes freezing to wheels.

Q. What pressure should be carried in the signal line? A. Forty-five pounds.

Q. How would you know whether or not there was main reservoir pressure in the signal line?

A. (1) By the whistle blowing when brakes were released; (2) by the inspection gage.

Q. How would you repair a broken signal pipe line? A. Usually, plug it.

Q. How much of the weight of a passenger car should be braked?

A. 90 per cent for full service application.

Q. Is this usual?

A. Yes; in freight service 60 per cent of the light weight of the car is usually braked.

Q. With the very best brakes, how do stops at different speeds compare?

A. On a level, directly with the square of the speed.

Q. At 60 miles an hour, how many feet a second will a train move?

A. Eighty-eight.

Q. What is the effect of cutting out the engine-truck brake?

A. The train will run considerably farther before a stop can be accomplished.

Q. What about the position of the shoes and angle of the brake-beam hangers?

A. Practice in this respect is reasonably correct; but incorrect angle of the hanger may cause either considerable loss of power or such an increase as may slide the wheels.

Q. In what position will the best results be obtained? A. If when the brakes are on, the hanger is parallel to a tangent to the wheel at the middle point of the brake shoe contact.

Q. What may be said about loss of brake efficiency by reason of low brake and reservoir pressures?

A. This is getting to be less, by reason of the pressure used being increased; now where the road passes through a hilly country, over 70 pounds are used, generally 110 pounds.

Q. What may be said of piston travel in connection with the brake?

A. It is often too great, and more often unequal in the various cars; some may have six inches and some ten; which makes smooth stopping difficult.

Q. What about the tension of the cylinder release spring, as causing loss of brake efficiency?

A. This is quite considerable, and probably can never be eliminated.

Q. How about the loss of efficiency from beam release springs?

A. This is the least excusable of all; the shoes should fall off from the wheels by their own weight. Their tension should be made and kept as low as possible.

Q. How about the loss by friction in foundation brakes? A. The amount of such loss has never been properly determined.

Q. What about insufficient leverage?

A. This comes from one of two causes; either the adoption of low standards of brake power, or mistakes in putting up foundation brakes.

CHAPTER LXXXIX

EXAMINATION OF FIREMEN

Q. By whom will the examination of firemen for position as enginemen be conducted?

A. By the road foreman of engines on the subjects given hereafter; and the trainmaster on such subjects as are under their respective jurisdictions; and by such other persons as the superintendent may direct.

Q. From whom will candidates be selected?

A. From those who have served as firemen at least three years.

Q. By seniority?

A. No; firemen must not rely upon seniority; the best interests of the company demand that vacancies shall be filled with men who have shown themselves most worthy of promotion; loyal, faithful, intelligent, and economical performance.

Q. Are the examinations in writing?

A. The examination will be either written, oral, or both, as the examiners may elect.

The examiners may vary the arrangement of the questions, or add to them, as they see fit, and if any answers of the candidate are not satisfactory, he will be questioned further on the doubtful points.

Q. On what else will the candidate be examined? A. In addition to this, he may be required to pass a practical examination on the locomotive, its operation, and the uses of its parts and attachments. He may be required to disconnect certain parts, such as rods, crossheads, links, and eccentrics, and put them together; to explain the uses of the shoes and wedges and the proper