TM 9-2330-388-14
Figure 4-55. Pressure Protection Valve
b.
Removal.
(1) Block semitrailer to prevent movement.
a.
General. The parking brake control valve is
basically an off-on, push-pull control valve. Its function is
(2) Exhaust air from system by opening drain
to release the fail-safe (spring) brakes for semitrailer
valves on bottom of air reservoirs.
movement by other than a towing vehicle.
(1) The valve can only be used when all air has
adapter (2) from end of valve.
been exhausted from the rear (primary) reservoir.
(4) Unscrew valve (3) from nipple (6).
(2) In the OUT position, the valve is closed, al-
lowing springs in the fail-safe chambers to apply braking
(5) Remove elbow (7) and bushing (6) from air
pressure.
reservoir if replacement is necessary.
(3) In the IN position, air is delivered from the
c.
Repair. No repair is authorized for the pressure
front (secondary) reservoir to the fail-safe chamber,
protection valve. Replace valve if malfunction occur
compressing the spring and releasing the brakes.
d.
Installation.
(4) When the trailer is connected to a towing
vehicle, air from the emergency line is applied to the pilot
(1) Apply antiseize tape (item 28, Appendix to
port of the valve, maintaining the OUT position.
male threads and install new nipple (6) in side port valve.
However, air from the emergency line is also directly
Turn valve and nipple into elbow (7) on air reservoir.
applied to the fail-safe chamber, compressing the spring
during normal towing operation.
(2) Install air line (1) and adapter (2) on vale
b.
Test. Internal leakage in the valve is indicated if
(3) Test and adjust valve (step a)
the spring brakes do not apply when the button is pulled
out and the system is at full pressure. External
(4) Remove blocking from semitrailer wheels.
4-118