TM-9-2330-356-14
SEMITRAILER, TANK: 5000 GALLON, BULK HAUL, SELF LOAD/UNLOAD M967 AND M967A1; SEMITRAILER, TANK: 5000 GALLON, FUEL DISPENSING, AUTOMOTIVE M969 AND M969A1; SEMITRAILER, TANK: 5000 GALLON, FUEL DISPENSING, UNDER/OVERWING AIRCRAFT M970 AND M970A1
TECHNICAL MANUAL; OPERATOR’S, UNIT, DIRECT SUPPORT, AND GENERAL SUPPORT MAINTENANCE MANUAL
OCTOBER 1990
TM-9-2330-356-14 - Page 233 of 528
TM 9-2330-356-14
Figure 4-80. Pressure Protection Valve.
b.
Removal.
(1) Block semitrailer wheels to prevent
movement.
(2) Exhaust air from system by opening drain
valves on bottom of air reservoirs.
(3) Remove air line (1, fig. 4-80) and adapter (2)
from end of valve.
(4) Unscrew valve (3) from nipple (6).
(5) Remove elbow (7) and bushing (8) from air
reservoir if replacement is necessary.
c.
Repair.
No repair is authorized for the pressure
protection valve. Replace valve if malfunction occurs.
d.
Installation.
(1)
Apply antiseize tape (item 28, Appendix E) to
male threads and install new nipple (6) in side port of
valve. Turn valve and nipple into elbow (7) on air reservoir.
(2)
(3)
(4)
Install air line (1) and adapter (2) on valve.
Test and adjust valve (step
a).
Remove blocking from semitrailer wheels.
4-47. Parking Brake Control Valve (Fig. 4-81)
a.
General. The
parking brake control valve is
basically an off-on, push-pull control valve. Its function is
to release the fail-safe (spring) brakes for semitrailer
movement by other than a towing vehicle.
(1) The valve can only be used when all air has
been exhausted from the rear (primary) reservoir.
(2) In the OUT position, the valve is closed,
allowing springs in the fail-safe chambers to apply braking
pressure.
(3) In the IN position, air is delivered from the
front (secondary) reservoir to the fail-safe chamber,
compressing the spring, and releasing the brakes.
(4) When the trailer is connected to a towing
vehicle, air from the emergency line is applied to the pilot
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
during normal towing operation.
b.
Test.
Internal leakage in the valve is indicated if
the spring brakes do not apply when the button is pulled
out and the system is at full pressure. External leakage can
be detected by applying soapy water around the valve
stem. No leakage is permitted. If the valve leaks or does
not operate, replace valve.
4-97
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