6-NFR DISTRIBUTING VALVE (cont)
(4) Application cylinder on the outer face of application piston is exhausted via passage 2a, through No. 24-A
double check valve, passages 26, 2, then 4 in the distributing valve, to exhaust.
(5) The release spring holds application piston in release position against application cylinder cover.
(6) The inner end of application piston, which is machined to form the exhaust valve seat, is moved away from
the rubber supply and exhaust valve to vent the brake cylinder passage.
(7) Main reservoir air is constantly present in the chamber and to application cylinder on the outer face of
application piston via passage No. 2, 26, No. 24-A double check valve, and passage 2a.
During a service brake application, the 6-NFR distributing valve functions as follows:
(1) Brake pipe pressure reduces, causing a difference in pressure between brake pipe and pressure chamber.
(2) The higher pressure in the pressure chamber and equalizing slide valve chamber causes the equalizing
piston and slide valve to move upward to service position where slide valve port connections are made.
(3) Upon the first movement toward service position, the graduating valve severs communication between brake
pipe and pressure chamber.
(4) Communication between pressure chamber and passage 2 is then made, allowing pressure chamber air to
flow to application chamber and to application cylinder on outer face of application piston via passages 2 and
26, 24-A double check valve, and passage 2a.
(5) Flow of pressure chamber air is continued until pressure has been reduced to slightly below brake pipe
pressure on the opposite side of the equalizing piston, at which time the piston and graduating valve are
moved to service lap position, terminating further flow of pressure chamber air to passage 2. Maximum
pressure in passage 2 is limited by the safety valve, which is connected to passage 2 by the safety valve
(6) Pressure that is developed in passage 2 and the application cylinder on the outer face of the application
piston causes the piston to move upward against the force of the release spring, first to seal the exhaust seat
against the underside of the supply and exhaust valve, and then to raise this valve from its supply seat to
allow main reservoir air to flow to brake cylinder cavity B and passage BC.
(7) Brake cylinder air pressure also builds up in chamber C on the inner face of application piston and
diaphragm via the stabilizing choke.