NO. 6 ET LOCOMOTIVE BRAKE 269 



maintained in the locomotive-brake cylinders, regardless of the 

 length of piston travel or the ordinary brake-cylinder leakage. 

 This is due to the fact that the supply of air for the locomotive- 

 brake cylinders is taken from the main reservoir, and when the 

 application piston 10 is in service lap position, due to either an 

 automatic or an independent application, a leak that reduces 

 brake-cylinder pressure will also reduce the pressure in the 

 exhaust-valve chamber of the distributing valve, which will 

 cause the application piston 10 and valve 5 to be moved to the 

 right by the greater pressure in the application cylinder. As 

 the application valve 5 is moved to the right, it will open com- 

 munication between chamber a and the brake cylinders through 

 port b in the application-valve seat and allow main-reservoir 

 air to pass to the locomotive-brake cylinders until the pressure 

 in the exhaust-valve chamber, and consequently in the brake 

 cylinders, is equal to that in the application cylinder, when the 

 application piston 10 will move valve 5 to the left far enough 

 to close port b. This action of the distributing valve will be 

 repeated each time the leaks reduce brake-cylinder pressure 

 below that in the application cylinder. It is possible for the 

 leaks from the brake cylinder to cause the application piston 

 10 and valve 5 to be moved to the right just far enough to 

 supply main-reservoir air to the brake cylinders through port b 

 as fast as it can escape through the leaks, in which case piston 

 10 would not move valve 5 back to lap position until the brakes 

 were released through the brake valves. 



If there are any leaks from the application cylinder of the 

 distributing valve, this maintaining feature will be destroyed, 

 because, with the brakes applied and the brake Valve in lap 

 position, the leak will continue to reduce the pressure in the 

 application cylinder. This will allow the greater pressure in 

 the exhaust-valve chamber to move the application piston 10 

 and its valves to release position and exhaust brake-cylinder 

 air. In such a case, however, it will be possible to hold on the 

 brakes by placing the independent brake valve in slow-applica- 

 tion position. 



Automatic Emergency Position With Quick-Action Cylinder 

 Cap. The valves in the quick-action cylinder cap do not 

 operate during a service application, but when an automatic 



