158 TRIPLE VALVES 



of brake-pipe air. Ordinarily, a braKe-pipe reduction of about 

 20 Ib. will cause a full application of the brakes. 



Releasing Brakes. To release brakes, either the brake-pipe 

 pressure must be increased above auxiliary pressure, or auxiliary 

 pressure must be reduced below brake-pipe pressure. The 

 usual method is for the engineer to allow the air stored in the 

 main reservoir to feed quickly into the brake pipe. When 

 the pressure on the brake-pipe side of piston 5 is sufficient to 

 overcome auxiliary pressure and the friction of the working 

 parts, the piston is forced upwards to release position, carrying 

 the graduating and slide valves with it. In this position, the 

 feed -groove is opened, and air from the brake pipe feeds through 

 to recharge the auxiliary. At the same time, the pressure in 

 the brake cylinder escapes through the exhaust port into the 

 atmosphere. 



Emergency Application. To apply brakes in an emergency, 

 it is necessary to make a sudden and heavy brake-pipe reduc- 

 tion. This sudden reduction causes piston 5 to move down 

 very quickly and, compressing the graduating spring, to trav- 

 erse the full length of its stroke. In this position, a direct 

 connection is established between the auxiliary and brake 

 cylinder across the upper end of the slide valve. Auxiliary 

 air passes direct into the brake cylinder without having first 

 to pass through the service ports of the slide valve. As the 

 large ports are used only in emergency position, they allow 

 the pressure in the auxiliary and brake cylinder to equalize 

 more quickly than do the smaller ports used in the service 

 position. With a plain triple, the brake sets more quickly 

 in emergency than in service, but not with greater force. To 

 get the full emergency action of the brakes with plain triple 

 valves, it is necessary to make a sudden reduction of over 

 20 Ib. in train-pipe pressure. After an emergency application, 

 the release of the brakes is accomplished in the same way as 

 after a service application. 



