6-NFR DISTRIBUTING VALVE (cont)
(8) As brake cylinder pressure in chamber C approaches application cylinder pressure on the opposite side of
the diaphragm and piston, the application piston is moved downward to allow the supply and exhaust valve
to be seated on its supply valve seat to terminate further flow of main reservoir air to the brake cylinder.
During brake release the 6-FNR brake valve functions as follows:
(1) An increase in brake pipe pressure moves the equalizing piston and slide valve to release position to connect
passage 2 and the application chamber to exhaust at port 4.
(2) Reduction of pressure in passage 2 and the application cylinder permits the higher brake cylinder pressure in
chamber C to move the piston out of contact with the exhaust valve seat, allowing brake cylinder air to flow
through chamber B, past the exhaust valve seat, to atmosphere through the brake cylinder exhaust passage.
During an emergency application, the 6-NFR distributing valve functions in the same manner as during a service
application, with the addition of the following:
(1) Main reservoir is connected to port 12 via the brake valve emergency valve.
(2) From port 12, main reservoir air flows through check valve and choke fitting to passage 2, past equalizing
piston, to the outer face of the application piston via passages 2 and 2b, 24-A double check valve, and
(3) Main reservoir pressure will increase to the value of the safety valve setting, where it is maintained by the
safety valve control choke and blowdown of the safety valve.
(4) Should the brake valve handle be moved out of EMERGENCY position, control pressure in passage 2 is
prevented from escaping from vent pipe No. 12 by a check valve. The pipe 12 choke ensures a positive
brake release when an emergency brake application is bailed off.
During the independent brake application, air pressure from passage 20 of the 26-C brake valve flows directly to
the outer face of the application piston via 24-A double check valve and passage 2a.