310 P C PASSENGER-BRAKE EQUIPMENT 



seat, to the application-chamber exhaust. As chamber-C pres- 

 sure reduces, chamber-0 pressure forces piston 78 forwards 

 to release position and exhausts the service-brake-cylinder air 

 through port n, chamber O, port k, and the service-cylinder 

 exhaust. The pressure in chamber M exhausts through the 

 ports em and en into port n and thence to the atmosphere. 



Graduate d-Release Position. With both piston 20 and 

 piston 3 in release position, the control valve is said to be 

 in graduated-release position, when the direct- and graduated- 

 release cap 18 is turned, so as to cut in the graduated-release 

 feature. If the cap 18 is turned into the position for direct 

 release, the control valve is said to be in direct-release posi- 

 tion. In both cases, the control valve is in release position, 

 but the term graduated or direct is prefixed to show whether 

 the cap 18 is turned so as to give a graduated or a direct 

 release of the brake. 



The application chamber and chamber C are open to the 

 atmosphere through ports I and V and the application-chamber 

 exhausts. If it were not for the graduated-release feature, the 

 release would be complete. However, the emergency reservoir 

 is connected with chamber E through port c, ports c and e of the 

 slide valve 22, port e, through the cap 18, port e, and port e of 

 the slide valve 8, into chamber E. Before this connection was 

 made, the chamber- pressure was reduced with the pressure- 

 chamber pressure when the brake application was made. The 

 emergency reservoir, on the other hand, is charged to normal 

 brake-pipe pressure. Therefore, air from the reservoir will flow 

 into chamber E, thence through port y, ports y and / of slide 

 valve 22, and port / of the seat, to the pressure chamber Z. 

 This pressure tends to increase the pressure in chambers E and 

 Z at the same time that brake-pipe air is increasing chamber- B 

 pressure. If chamber- .E pressure rises faster than chamber- .B 

 pressure, the differential pressure thus created on piston 3 will 

 tend to move the piston toward the graduated-release lap posi- 

 tion, and either wholly or partly stop the flow of air from the 

 application chamber to the atmosphere and from the emergency 

 reservoir to chamber E. If brake-pipe pressure increases very 

 slowly, the increase in differential pressure may be sufficiently 

 rapid to cause the release piston and graduating valve to 



