TM 9-2330-356-14
b.
Removal.
a.
General. The parking brake control valve is
(1) Block semitrailer wheels to prevent
basically an off-on, push-pull control valve. Its function is
movement.
to release the fail-safe (spring) brakes for semitrailer
movement by other than a towing vehicle.
(2) Exhaust air from system by opening drain
valves on bottom of air reservoirs.
(1) The valve can only be used when all air has
been exhausted from the rear (primary) reservoir.
(3) Remove air line (1, fig. 4-80) and adapter (2)
from end of valve.
(2) In the OUT position, the valve is closed,
allowing springs in the fail-safe chambers to apply braking
(4) Unscrew valve (3) from nipple (6).
pressure.
(5) Remove elbow (7) and bushing (8) from air
(3) In the IN position, air is delivered from the
reservoir if replacement is necessary.
front (secondary) reservoir to the fail-safe chamber,
compressing the spring, and releasing the brakes.
c. Repair. No repair is authorized for the pressure
protection valve. Replace valve if malfunction occurs.
(4) When the trailer is connected to a towing
vehicle, air from the emergency line is applied to the pilot
Installation.
d.
port of the valve, maintaining the OUT position.
However, air from the emergency line is also directly
applied to the fail-safe chamber compressing the spring
male threads and install new nipple (6) in side port of
during normal towing operation.
valve. Turn valve and nipple into elbow (7) on air reservoir.
Test. Internal leakage in the valve is indicated if
b.
(2) Install air line (1) and adapter (2) on valve.
the spring brakes do not apply when the button is pulled
out and the system is at full pressure. External leakage can
(3) Test and adjust valve (step a).
be detected by applying soapy water around the valve
stem. No leakage is permitted. If the valve leaks or does
(4) Remove blocking from semitrailer wheels.
not operate, replace valve.
