308 P C PASSENGER-BRAKE EQUIPMENT 



against the slide valve 22. The graduating valve 24 will then 

 cover or blank port / and thus close communication between the 

 chambers F and Z. Each succeeding reduction, provided it 

 does not produce equalization between chambers Y and Z, will 

 cause piston 20 to move to overreduction position and, finally, 

 back to overreduction lap position. Also, in this position, the 

 graduating valve 24 blanks the port v leading to chamber K. 

 Therefore, in case the brake is held applied in overreduction 

 position for a sufficient length of time and the leakage from the 

 application chamber is so great that sufficient service-reservoir 

 air cannot leak past the piston-packing ring, from chamber H 

 into chamber G, to supply it, the service-reservoir charging 

 valve will finally be moved upwards, opening direct connection 

 between the service reservoir and the application chamber 

 through port g, chamber H, ports v and y, port / in slide valve 

 22, and port /. Should an overreduction reduce the brake-pipe 

 pressure below the pressure of equalization of chambers Y and 

 Z, quick-action will result. 



Preliminary Release Position. In releasing brakes, a rise in 

 brake-pipe pressure above the pressure in chambers D and E 

 will cause the piston 20 to move toward release position. The 

 equalizing piston 20 moves first, because the release piston and 

 valves are designed so that they will require a greater differential 

 pressure to move them than is necessary to move the equalizing 

 piston and valves. When the equalizing slide valve 22 has been 

 moved to preliminary release position, it is held momentarily 

 with port z of the slide valve in register with port y of the seat. 

 In this position, the pressure chamber Z is connected with 

 chamber F by port /, ports w and i of the slide valve, and port i 

 of the seat. Chamber-Z pressure in chamber F and the force 

 of the equalizing-piston stop-spring 30 insure the slide valve 22 

 sufficient time in the preliminary release position to reduce 

 chamber- pressure below that in the brake pipe by an amount 

 that makes positive the return of piston 3 to release position. 

 Chamber-E air exhausts through port y, port z of the slide 

 valve, cavity dw of the graduating valve, and port w of the 

 slide valve, to the reduction-limiting-chamber exhaust w. 



Secondary Release Position. The reduction of chamber-^) 

 pressure results in the release piston moving to release position 



