PC PASSENGER-BRAKE EQUIPMENT 315 



108 to the atmosphere through port p and cavity * in slide 

 valve 4- Emergency-reservoir pressure in chamber R forces 

 the emergency piston 108 and the slide valve 110 to their emer- 

 gency positions, thereby connecting the emergency-brake cyl- 

 inder with the emergency reservoir through port c, chamber 

 R, and port o and allowing the pressure to equalize in the cylin- 

 der and reservoir; also, chamber R is connected to the service 

 cylinder through port en and port n, thus allowing all the ser- 

 vice- and emergency-brake cylinders and reservoirs to equalize 

 with one another. 



Chamber M, behind piston 78, is connected to the atmosphere 

 through ports em, the cavity in the emergency slide valve, 

 port o', and the emergency-cylinder exhaust. This is done to 

 assist the pressure in chamber C moving the piston 78 quickly 

 and positively to emergency position. It will be noted that in 

 emergency position the pressure chamber Z is connected to 

 chambers D and E, and chamber D is connected to chamber Y. 

 The purpose of this is to equalize the pressure in all the cham- 

 bers and reservoirs and to insure sufficient pressure on all the 

 slide valves and graduating valves to hold them to their seats. 



Quick- Action Valve Closed. The closing of the quick-action 

 valve 133, after making a local vent to the atmosphere to trans- 

 mit quick action serially throughout the train, is accomplished 

 as follows: As soon as quick action occurs, emergency-cylinder 

 pressure and, therefore, chamber- T pressure, begins to rise, 

 while the pressure in chamber W and the emergency reservoir 

 begins to fall. When the pressures in chambers T and IV 

 become nearly equal, the spring of valve 139 closes the valve 

 and stops the flow of air into chamber W. The air thus trapped 

 in chamber W escapes through the leakage hole Ih in the piston 

 131 to the atmosphere through port qx and the quick-action 

 exhaust. This balances the pressure on the two faces of piston 

 131, and the spring of valve 133 and brake-pipe pressure closes 

 the valve 133 and stops the escape of brake-pipe air to the 

 atmosphere. If the brake-pipe pressure is entirely depleted, 

 the spring of valve 133 will close the valve and thus insure 

 against a loss of brake-pipe air when a release is made imme- 

 diately after the quick-action application. 



