4-11. AUTOMATIC BRAKE VALVE (cont)
(2) Brake pipe air pressure reduces as follows:
(a) Pressure reduction in the equalizing reservoir will be felt on the outer side of the relay valve diaphragm.
With the inner face of the diaphragm at brake pipe pressure, the pressure difference will force the
diaphragm outward, pulling the valve stem with it.
(b) The valve stem will open the exhaust seat of the relay valve. Brake pipe air pressure will be vented out
relay valve exhaust port, causing a brake pipe pressure reduction at service rate.
(c) Brake pipe air pressure will continue to vent until pressure on the inner face of relay valve diaphragm
and in the brake pipe balances with the pressure of the equalizing reservoir. Relay valve will then
assume lap position.
(d) Equalizing reservoir air pressure can be reduced in steps, by handle movement, in about 2-psi (14 kPa)
increments until a pressure reduction of 23 to 26 psi (159 to 179 kPa) is attained at FULL SERVICE
(3) Lap position will be maintained as follows:
(a) Reduction of equalizing reservoir air pressure through regulating valve exhaust will continue until
pressure on the valve diaphragm balances with the adjusting spring tension which has been weakened
by handle cam movement.
(b) The valve will then move to close the exhaust seat and assume lap position.
(4) Release of service brake application functions as follows:
(a) Movement of brake handle toward RELEASE position will cause regulating valve cam on the handle to
move the regulating valve assembly toward the adjustment spring, increasing the spring tension and
opening the supply seat of the valve.
(b) Equalizing reservoir charging air pressure will increase at the re
gulating valve; however, it will not
increase in equalizing reservoir charging pipe 15 because the check on the equalizing reservoir cutoff
valve remains seated until the brake valve handle is placed in RELEASE position.