124 ENGINEER'S BRAKE VALVES 



and allows a small quantity of air to escape into the exhaust 

 cavity ex which makes sufficient noise to attract the engineer's 

 attention to the position in which the valve handle is standing. 

 The small groove in the face of the rotary valve that connects 

 with port 5, extends to port p in the valve seat, allowing main- 

 reservoir pressure to flow to the excess-pressure head of the 

 pump governor. 



Running Position. The running position is the proper posi- 

 tion of the handle when the brakes are charged and ready 

 for use, when the brakes are not being operated, and when the 

 locomotive brakes are to be released. In this position, cavity / 

 in the rotary valve connects ports b and d in the valve seat, 

 affording a large direct passage from the feed-valve pipe to 

 the brake pipe, so that the latter will charge up as rapidly as 

 the feed-valve can supply the air, but cannot attain a pres- 

 sure above that for which the feed-valve is adjusted. Cavity k 

 in the rotary valve connects ports c and g in the valve seat, 

 so that chamber D and the equalizing reservoir charge uni- 

 formly with the brake pipe, keeping the pressure on the two 

 sides of the equalizing piston equal. Port 5 in the rotary 

 valve registers with port p in the valve seat, permitting main- 

 reservoir pressure, which is present at all times above the 

 rotary valve, to pass to the excess-pressure head of the pump 

 governor. Port h in the rotary valve registers with port / in 

 the seat, connecting the distributing-valve release pipe through 

 the exhaust cavity ex with the atmosphere. 



Service Position. The service position gives a gradual reduc- 

 tion of brake-pipe pressure to cause a service application. 

 Port h in the rotary valve registers with port e in the valve seat, 

 allowing air from chamber D and the equalizing reservoir to 

 escape to the atmosphere through cavities o, in the rotary valve, 

 and ex, in the valve seat. Port e is restricted so as to make 

 the pressure in the equalizing reservoir and chamber D fall 

 gradually. As all other ports are closed, the fall of pressure 

 in chamber D allows the brake-pipe pressure under the equal- 

 izing piston to raise it, and unseat its valve, allowing brake- 

 pipe air to flow to the atmosphere gradually through the open- 

 ing marked exhaust, Fig. 1. When the pressure in chamber D 

 is reduced the desired amount, the handle is moved to lap 



