162 TRIPLE VALVES 



brake is a vastly different proposition from controlling an 

 eighty-car part-air train. The length as well as the volume 

 of the brake pipe is practically twice that of the original 

 fifty-car train." Therefore, the difficulty experienced in 1887 

 in emergency applications with the plain automatic brake is 

 now experienced in service applications of the automatic brake; 

 that is, the interval between the application of the brake on 

 the first car and that on the last car is so great in service 

 applications that if a heavy reduction is made without taking 

 due precautions a terrific shock will be caused by the rear 

 cars running in the amount of the slack and colliding with 

 the front cars held by a good application of the brake. In 

 addition, the recoil of the rear cars after the shock, aided by 

 the action of the compressed springs and the application of 

 the brake taking hold on them, tends to snap the train in two. 

 Another serious difficulty, due to the increased brake-pipe 

 volume (which is twice as great as with a fifty-car train) and 

 to the increased back flow of air into the brake pipe from the 

 auxiliaries, due in turn .to the slower reduction, is that the 

 time necessary to make a given brake-pipe reduction is doubled. 

 This makes the time of application twice as long, which makes 

 the application qf the rear brakes more uncertain and very 

 materially lengthens the distance required to make a stop. 

 Every second lost at high speed in getting the brake fully 

 applied adds many feet to the length of the stop. 



In releasing brakes, the interval between the release of the 

 first brake and the last brake is so great that the brakes on a 

 good portion of the train release and the slack runs out before 

 the brakes on the rear portion release, tending to break the 

 train in two. Also, the brake is slow in releasing, and the 

 rear brakes are especially slow on account of the increased 

 brake-pipe volume to be discharged and the increased size of 

 the auxiliary reservoirs of the large capacity cars that are 

 taking air from the brake pipe during recharge. As the brakes 

 are slow in applying and releasing, both the danger and the 

 time of making a stop and a start are increased. 



The difficulty of brake control increased with the length 

 of the train above the limit of fifty cars. However, the 

 brake manufacturers, profiting by their experience, foresaw 



