PC PASSENGER-BRAKE EQUIPMENT 305 



position, compressing the application-piston spring 93. In 

 this position, the exhaust valve closes the service-cylinder 

 exhaust ports k. The port in the application slide valve is 

 opened and permits air from the service reservoir to flow through 

 port g and chamber N into chamber O, and through port n to 

 the service-brake cylinder, applying the brake with the pressure 

 developed by that cylinder. The pressure in chamber M is 

 maintained equal to that in the service cylinder through the 

 port en, the cavity in the emergency slide valve, and the port 

 em. Air will continue to flow into the service cylinder and 

 chamber M until the pressure becomes about equal to the 

 application-chamber pressure on the other face of the piston 

 78, when the application-piston spring 93 returns the piston 78 

 and slide valve back to service lap position. This holds the 

 brakes applied with a service-brake-cylinder pressure about 

 equal to the pressure admitted to chamber C and the appli- 

 cation chamber. The operation of the application portion of 

 the control valve for all operations of this brake is exactly 

 the same as the operation of the application portion of the 

 distributing valve of the ET equipment. In service position, 

 the emergency-brake cylinder and the reduction-limiting cham- 

 ber are open to the atmosphere. 



Service Lap Position. As there is direct connection between 

 the chambers D, E, and Z in service position, it follows that any 

 reduction of pressure in chamber D will produce a like pressure 

 in chambers E and Z. When a brake-pipe reduction is made 

 to apply the brake and the parts move to service position, air 

 from chamber Z flows by way of chamber D into chamber C 

 and chamber X. The air continues to flow from chamber D 

 until the pressure is reduced sufficiently below brake-pipe pres- 

 sure to overcome the resistance of the piston 20, when the equal- 

 izing valve will be moved back to service lap position. It 

 makes no difference in the operation of the control valve whether 

 the piston S moves to lap position or not, because it is the equal- 

 izing graduating valve that laps port /, thus stopping the flow of 

 air into the application chamber X and holding the pressure that 

 was built up in chamber C. The pressure in chamber C deter- 

 mines the pressure in the brake cylinder, because brake-cylin- 

 der pressure is automatically maintained equal to chamber-C 

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