10. Failure of the feed-pumps, injector or check-valve. 11. Breaking or bursting of a cylinder, cylinder-head, steam-chest, or steam-pipe. 12. Breaking or getting loose of the piston or cross-head or bending of the piston-rod. 13. Breaking or bending of a connecting-rod or crank-pin. 14. Breaking of a tire, wheel or axle. 15. Breaking of a spring, spring-hanger or equalizer. 16. Breaking of a frame. 17. Breaking or getting loose of a part of the valve-gear. 18. Failure of the throttle-valve. 19. Breaking of a coupling. QUESTION 503. _What should be done to prevent a collision when two trains are approaching each other?_ _Answer._ The obvious thing to do is to stop the trains as soon as possible. This is done by applying the brakes at once with all their power, and then reversing the engine, although it is best not to do the latter until the train is somewhat checked, as there is always danger of bursting the cylinder or breaking the cylinder-heads, piston or connections if an engine is reversed suddenly at a high speed. Of course the higher the speed, the greater is the danger of injury from this cause, and therefore it is best, if there is time, first to check the speed of the train before reversing the engine. When the engine is reversed, the sand-valves should be opened so as to increase the adhesion of the wheels, so that when their motion is reversed they may check the speed of the train as soon as possible. On perceiving danger ahead the order of procedure should be as follows: 1. Shut the throttle-valve. 2. If the train is equipped with hand brakes alone, blow the danger signal for their application, or if the train has a continuous brake, apply it with its full force. 3. Reverse the engine and open the throttle and the sand valves. 4. If a collision is inevitable, shut the throttle-valve before the engines meet, because if it is left open, after the collision and when the speed of the train is checked, the engine, if not disabled, will by its own power crush through the wreck and thus do additional damage. QUESTION 504. _What should be done if a standing train should see another train approach it and there should be danger of a collision?_ _Answer._ The locomotive runner of the standing train should start his engine in the same direction as the approaching train is running, as quickly as possible, because the shock of the collision will be very much lessened if both trains are moving in the same direction compared with what it would be if one was standing still. QUESTION 505. _What should be done to avoid a collision at a railroad crossing?_ _Answer._ As was explained in answer to Question 485, trains should always come to a dead stop before crossing another railroad on the same level. If, however, through any means danger of such a collision should be incurred, then evidently the one train should be stopped and the other moved out of the way as soon as possible.