TRIPLE VALVES 183 



amount of the reduction is not so great. As a result of this 

 serial action, the time interval between the operation of the 

 first and last brakes on a long train is greatly reduced; also, 

 with a long train of K triples, the time required for the air 

 to exhaust from the brake-pipe exhaust valve of the brake 

 valve for a given reduction will be greatly reduced below the 

 time required with a train of H triples. The venting of brake- 

 pipe air into the brake cylinder results in a pressure on equali- 

 zation that is about 1 Ib. higher. 



After the triple piston has moved the slide valve to quick- 

 service position, the slide valve does not move again until 

 the brake is released or a sufficient reduction is made in brake- 

 pipe pressure to move it to full-service or emergency position; 

 the graduating valve controls the quick-service ports in the 

 slide valve, so that they are opened each time the graduating 

 valve opens the service port and closed each time the piston 

 moves the graduating valve to lap position. 



The quick-service feature of the K triple valve operates 

 only when the brake-pipe reduction is being made at less than 

 the proper rate, as when the train is long. With a short train, 

 the brake valve can reduce brake-pipe pressure as fast as is 

 necessary, and the local reduction is not desirable; hence, 

 under such conditions, the quick-service feature automatically 

 goes out of service by the triple valve going to full-service 

 position. 



Full-Service Position. The strength of the graduating 

 spring 22 is such that when the reduction in the brake pipe 

 is being made at the proper rate, the difference in pressure 

 on the triple piston will be great enough to compress the gradu- 

 ating spring sufficiently to permit the slide valve to assume 

 full-service position. Thus, as the quick-service feature is 

 not needed, it is automatically cut out of commission. 



When the brake-pipe reduction is slower than it should be, 

 as when the train is long or during moderate reductions, the 

 service port is opened sufficiently to prevent enough differ- 

 ence of pressure from being formed to compress the graduating 

 spring 8. 



With the triple valve in full -service position, the graduating 

 port and brake-cylinder port register fully. The quick-service 



