PC PASSENGER-BRAKE EQUIPMENT 309 



while the equalizing piston still momentarily remains in position 

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

 This position is called the secondary release position. With 

 piston 3 in release position, chamber F is connected with the 

 emergency-piston exhaust port Ex by port * and cavity i 

 of the release slide valve. At the same time, the pressure 

 chamber Z is connected to the same port * and chamber F by 

 the port /, ports / and i in the slide valve 22, and port *. The 

 exhaust of chamber-Z air through port i tends to maintain 

 the pressure in chamber F temporarily while slide valve 4 is 

 increasing the port opening from chamber F to the atmosphere 

 to insure the exhaust from chamber E being held open until 

 after the release piston is in release position. As the movement 

 of the release slide valve toward release position increases the 

 size of the opening of port *, the pressure in chamber F gradually 

 decreases until it is low enough for the differential pressure 

 acting on the piston 20 to start the piston toward release 

 position. This movement of the slide valve 22 gradually 

 restricts and, finally, closes port /, thereby stopping the flow 

 of chamber-Z air into port i and chamber F. Chamber-/ 5 " air 

 then exhausts to the atmosphere, and the equalizing piston is 

 moved to release position and held there. When the slide 

 valve 4 assumes release position, and before the slide valve 22 

 moves to release position, a second passage is made for the 

 exhaust of chamber- .E air to the atmosphere. 



In the release position of slide valve 4> port e of the slide 

 valve registers with port e of the valve seat; therefore, cham- 

 ber-E air can pass through the ports e, the cavity w of the slide 

 valve, and the reduction-limiting-chamber exhaust w. This 

 connection, like the connection between ports z and y, is but 

 momentary and is simply a second, or additional, opening from 

 chamber E to the atmosphere. It should be understood that a 

 brake-pipe pressure of from 1J to 2 Ib. above that in the appli- 

 cation chamber X is all that is necessary to move the parts 

 through the momentary successive positions of preliminary and 

 secondary release to release position. 



With release slide valve 4 in release position, chamber-C and 

 application-chamber air exhaust to the atmosphere through 

 the port /, ports / and I' in slide valve 22, and port /' in the 



