114 ENGINEER'S BRAKE VALVES 



Running Position. In running position, air from the main 

 reservoir passes through the feed-valve attachment into the 

 brake-pipe. The air continues to flow thus until the brake- 

 pipe pressure reaches 70 lb., when the feed- valve attachment 

 closes. As air passes through the feed- valve attachment, 

 some of it passes up into a cavity in the rotary valve and 

 down through a port into chamber D, the chamber above 

 the equalizing piston 18. Connection is thus maintained 

 between the brake pipe and chamber D, that is, between both 

 sides of the equalizing piston 17. The black gauge hand is 

 piped to the equalizing-reservoir connection at union swivel 1 7, 

 and, as in running position there is a port connection between 

 the brake pipe and chamber D through the cavity in the 

 rotary and a port, the black hand must, in this position, indi- 

 cate both chamber D and brake-pipe pressures. The same 

 movement that changes the rotary from full-release to running 

 position closes the warning port. 



Lap Position. In lap position, the rotary has been moved 

 around so as to close all connections. 



Service Position. In service position, the rotary has been 

 moved so that a groove in the face of the rotary valve connects 

 the preliminary-exhaust port in the rotary seat with a port, 

 which leads into the direct-application-and-exhaust port. A 

 direct connection is thus established between chamber D and 

 the atmosphere, and air from chamber D can pass to the 

 atmosphere. The reduction of the pressure in chamber D 

 causes the equalizing piston to rise and open the brake-pipe 

 exhaust valve, thus producing a brake-pipe reduction. 



Emergency Position. In emergency position, the rotary has 

 been moved around so that its cavity connects a large port 

 leading to the train pipe with the exhaust port leading to the 

 atmosphere. The opening of these large ports causes a sudden 

 brake-pipe reduction, which gives an emergency application 

 of the brakes. Also, a groove in the rotary valve connects a 

 port from chamber D with a groove leading to the atmosphere, 

 thus exhausting the air from chamber D and allowing the black 

 hand of the gauge to drop to zero. 



