132 ENGINEER'S BRAKE VALVES 



valve can pass through the distributing-valve release pipe to 

 the independent brake valve, thence into the release pipe, and 

 out to the atmosphere through the automatic brake valve, 

 provided the latter also is in running position. To release the 

 locomotive brakes through the automatic brake valve, both 

 brake valves must be in running position. If the automatic 

 brake valve is in running position and the locomotive brakes 

 are being operated by the independent brake valve, they can 

 be released by placing the independent brake valve in running 

 position, because air from the application cylinder of the dis- 

 tributing valve can then pass through the release pipe and 

 automatic brake valve to the atmosphere. 



Lap Position. The lap position is used when it is desired 

 to blank all ports in the rotary-valve seat and prevent air from 

 passing through the brake valve. When the valve handle is 

 in this position, all ports are blanked so that air cannot pass 

 through the brake valve. With the independent brake valve 

 in lap position, the locomotive brakes can be applied by means 

 of the automatic brake valve by reducing brake-pipe pressure, 

 but they cannot be released through the automatic brake valve. 



Slow-Application Position. The slow-application position 

 is to be used when it is desired to apply the locomotive brakes 

 lightly or gradually and independently of the train brakes. 

 Also, when the locomotive is standing, this position is used to 

 maintain brake-cylinder pressure so as to prevent the locomo- 

 tive brakes from leaking off through brake-cylinder leakage 

 and thus allow the engine to start when standing on a grade 

 or when the throttle is leaking. When the handle of the valve 

 is placed in this position, the ports in the rotary valve and 

 its seat are still blanked as in lap position, except that one port 

 in the face of the rotary valve registers with a port in the rotary- 

 valve seat. This allows air at a pressure of 45 Ib. to pass 

 from the reducing- valve pipe into the application-cylinder pipe 

 and the application cylinder of the distributing valve, thus 

 applying the locomotive brakes slowly. To graduate the 

 application of the locomotive brakes, the handle should be 

 moved to slow-application position until the desired pressure 

 is obtained in the application cylinder, when it should be 

 returned to lap position. The red hand on the duplex gauge 



