TM 55-2210-223-34
TO 45A2-2-14-22
4-11.
AUTOMATIC BRAKE VALVE (cont)
TEST (cont)
(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 regulating 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.
c.
SUPPRESSION Position. This portion of the brake handle is provided for reset of a safety control penalty
brake application. Although this position is to the right of FULL SERVICE position, no further reduction of
equalizing reservoir pressure will be made beyond that already attained at FULL SERVICE.
(1) When brake handle is placed in SUPPRESSION position, suppression valve spool will be displaced fully
inward by the handle cam.
(2) Main reservoir air pressure will be trapped in the spring chamber of the spool and port 3 will continue to be
vented.
(3) Main reservoir air pressure will be directed to port 26 and suppression pipe port 8; the lock-over pipe will
be blocked by the valve spool in suppression position.
(4) Air pressure on port 26 is used to suppress the safety control brake application valve, and blocking of port
8 will reset the safety control brake application valve.
d.
HANDLE-OFF Position. This position is provided to allow the brake valve to be cut out when the locomotive is
trailing.
(1) In HANDLE-OFF position, suppression valve is positioned as it is in SUPPRESSION position. The
regulating valve cam, however, is moved to allow the regulating valve spool to move fully away from its
adjustment spring tension.
(2) If the brake valve handle is placed in HANDLE-OFF position and removed, equalizing reservoir air
pressure will be reduced to atmosphere and safety control will be suppressed, allowing the brake valve to
be cut out and left unattended.
4-50
