312 PC PASSENGER-BRAKE EQUIPMENT 



main-reservoir air supply through the brake valve. Connec- 

 tion is then made between the service reservoir, the emergency 

 reservoir, the pressure chamber, and the brake pipe, and the 

 final stage of the recharging of all these parts is accomplished 

 by air from the main reservoir passing through the brake valve. 



As main-reservoir air has the brake pipe alone to recharge 

 during the first stage of the recharge, the rise in brake-pipe 

 pressure is much more rapid than with the older types of 

 brakes; hence, the release of the brakes throughout the length 

 of the train is much more sure and positive than with the 

 other types. 



Release Lap Position. The release of the brake is accom- 

 plished by placing the brake valve in release position so as to 

 raise brake-pipe pressure, recharge the brake pipe, and move 

 the pistons 20 and 3 to release position. If the handle of the 

 brake valve is left in release position, the brake will release 

 in one continuous exhaust of brake-cylinder air without any 

 graduations of brake-cylinder pressure. On the other hand, 

 if the brake valve is moved to release position for a time and is 

 then moved to lap, only part of the brake-cylinder pressure 

 will be exhausted, and by repeating the movement of the brake 

 valve from release to lap positions the brake can be gradu- 

 ated off. In graduating off the brake, while the brake pipe is 

 recharging through the brake valve, the pressure chamber and 

 chamber E are recharging with air from the emergency reser- 

 voir. If, the brake-valve handle is moved to lap position when 

 the brake pipe is only partly recharged, the continued flow of 

 air from the emergency reservoir with chamber E will raise the 

 pressure in chamber E above that in chamber B, which is now 

 stationary, and cause the release piston 3 to move to graduated- 

 release lap position. In this position, the shoulder of the stem 

 of piston 3 is against the slide valve 4, the flow of air into cham- 

 ber E ceases, and the graduating valve blanks port I and stops 

 the exhaust of air from chamber C and the application chamber. 

 This holds chamber-C pressure constant, and the application 

 portion maintains brake-cylinder pressure constant and equal 

 to chamber-C pressure. If the brake valve is again moved to 

 release position and then back to lap position, piston 3 will be 

 moved to release position and then back to rele&se lap position, 



