4-13. 6-NFR DISTRIBUTING VALVE (cont)
Upon the first movement toward service position, the graduating valve severs communication between
brake pipe and pressure chamber.
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.
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 control choke.
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.
Brake cylinder air pressure also builds up in chamber C on the inner face of application piston and
diaphragm via the stabilizing choke.
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
During brake release the 6-NFR brake valve functions as follows:
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.
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.