4-11. AUTOMATIC BRAKE VALVE (cont) TEST (cont)
(c) From port 15, equalizing reservoir air pressure flows to the equalizing reservoir, to the air gages, and to
(d) Equalizing reservoir air pressure is directed through an orifice from the charging passage to the
diaphragm of the regulating valve.
(e) Through port 5, the equalizing reservoir air pressure is directed to the outer side of the relay valve
(3) Brake pipe air pressure is developed as follows:
(a) Equalizing reservoir air pressure on the outer side of the relay valve diaphragm forces the diaphragm
and valve stem inward. Inward movement of the valve stem opens the supply valve seat, and main
reservoir air enters the brake pipe charging passage.
(b) The brake pipe charging pressure flows to the brake pipe cutoff valve, which opens when the charging air
pressure is about 25 psi (172 kPa). Air then flows around the sealed vent valve, into the brake pipe
passage, and out port 1.
(c) Brake pipe charging air pressure is also directed through an orifice to the inner face of the relay valve
diaphragm, where it develops a counteracting force to the equalizing reservoir force on the outer face of
the diaphragm. When these forces are equal, brake pipe charging cuts off.
(d) Brake pipe air pressure is also connected through a passage in the brake valve to spillover check valve
B on the bottom of the handle portion, where is is made available to the spool of the cutoff pilot valve in
(4) Lap position is maintained as follows:
(a) When the equalizing reservoir charging air pressure in pipe 15 and on the inner face of the regulating
valve diaphragm are equal to the adjustment spring tension of the regulator valve, the valve spool
moves toward the adjustment spring. This moves the supply valve against its seat and stops charging of
the equalizing reservoir. This is selflapping. If a leak in the equalizing reservoir occurs, the diaphragm
pressure weakens and the regulator valve moves to supply and the equalizing reservoir pressure is
brought back up to make the adjustment spring tension. This is equalizing reservoir pressure