182 TRIPLE VALVES 



into the auxiliary until the pressures are equalized near enough 

 for the check- valve spring to seat the check- valve, after which 

 the auxiliary charges through the feed-groove alone. 



Quick-Service Position. When a service reduction is made 

 in the brake-pipe pressure at the brake valve, the pressure on 

 the brake-pipe side of the triple piston is reduced faster than 

 auxiliary-reservoir pressure can reduce through the feed-groove. 

 This produces a difference of pressure on the two faces of the 

 piston, and when this difference becomes about 2 Ib. per 

 sq. in., the auxiliary-reservoir pressure, being the greater, 

 forces the piston forwards to application position, taking the 

 graduating valve 7 with it and closing the feed groove. This 

 movement of the triple piston first causes the graduating 

 valve to uncover the graduating port and to connect two ports 

 in the back of the slide valve through the cavity in the valve; 

 then the shoulder on the triple -piston stem engages the slide 

 valve and moves it to application position. If the difference 

 in pressure on the two faces of the triple piston is not sufficient 

 to compress the graduating spring 22, these parts will be held 

 in quick-service position. 



In this position, the triple piston is close to or against the 

 graduating stem but does not compress the graduating spring. 

 The slide valve cuts off the connection between the exhaust 

 ports so that brake-cylinder pressure cannot pass to the 

 atmosphere. Auxiliary -reservoir air now flows into the brake 

 cylinder and applies the brakes; also, brake-pipe pressure, 

 raising check- valve 15, passes to the chamber above the emer- 

 gency piston, from which place it can pass the emergency 

 piston, which fits loosely in its cylinder, to the brake cylinder. 

 Ports' leading to the chamber above the emergency piston 

 are so restricted that the flow of air through them, when con- 

 nected, is not great enough to raise sufficient pressure above 

 the emergency piston to force it down and cause an emergency 

 action of the triple, but the air that passes to the brake cylinder 

 reduces the brake-pipe pressure locally at each triple valve 

 just enough to cause the next triple valve to operate promptly. 

 This local reduction acts to transmit quickly and uniformly 

 the brake-valve reduction from car to car in a manner similar 

 to the serial action during an emergency application, only the 



