260 NO. 6 ET LOCOMOTIVE BRAKE 



Automatic Service Position. When making an automatic 

 service application of the brakes, brake-pipe pressure is 

 reduced. This reduces the pressure in chamber p of the 

 distributing valve, and as the feed-groove is very small, the 

 pressure in chamber p can reduce faster than the air can pass 

 back through the feed-groove v. The greater pressure in the 

 equalizing- valve chamber will then move the equalizing pis- 

 ton 26 to the right. This movement cuts off communication 

 between the equalizing-valve chamber and chamber p, by 

 closing the feed-groove v. The graduating valve 28, which 

 fits snugly between the shoulders on the piston stem, is also 

 moved on the back of the equalizing valve so as to uncover 

 the upper end of port z in the equalizing valve, and cavity t in 

 the graduating valve 28 connects the ports r and 5 in the 

 top of the equalizing valve. By this time, the shoulder on the 

 end of the piston stem has engaged the equalizing valve, and a 

 further movement of piston 26 carries the equalizing valve with 

 it and all these parts will assume service position. When the 

 valves are in this position, cavity k in the face of the equalizing 

 valve is moved from over ports h and w, so that these ports are 

 no longer connected with the exhaust port i. Cavity n in the 

 face of the equalizing valve connects ports h and w in the valve 

 seat, thus opening communication between the application cyl- 

 inder and the application chamber; also, port r is moved 

 over port h, and port 5 over port I. As ports r and 5 are con- 

 nected through cavity t in the graduating valve 28, this opens 

 communication between the application cylinder, the applica- 

 tion chamber, and the safety valve. Port z in the equalizing 

 valve registers with port h in the valve seat. This allows air 

 from the equalizing- valve chamber and the pressure chamber 

 to flow through ports z and h into passage h, thence to the 

 application cylinder, and also through port h, cavity n, and 

 port w into the application chamber. The equalizing piston 

 stands against the graduating sleeve, but does not compress 

 the graduating spring, because of its resistance and the fact 

 that the slightly greater pressure in the equalizing- valve cham- 

 ber is gradually reduced by the air passing through port z. If 

 the pressure in the equalizing- valve chamber should be greatly 

 in excess of the pressure in chamber p, the graduating spring 



