relief valve should be connected to the brake port. See
figure 12-44. Operation of the manual lever through five
full strokes should pump hydraulic fluid through the
relief valve. Leakage at the piston rod gland should not
exceed 1 drop at this time. Not less than 0.75 cubic inch
of fluid should flow from the relief valve during anyone
complete stroke cycle of the manual lever. There should
be no evidence of binding at any time during these tests.
BRAKE SHUTTLE VALVE
Shuttle valve maintenance is generally limited to
repairing leakage. External leakage may usually be
repaired by tightening the end caps. If this does not stop
the leakage, the end cap O-ring should be replaced.
Internal leakage can usually be repaired by
removing and flushing the unit with clean, hydraulic
fluid. Excessive heating is a good indication of internal
leakage through a shuttle valve. Excessive cycling of the
emergency system pump is also an indication of a leaky
After an emergency system has been operated, all
emergency system pressure should be bled off as soon
as possible and the normal system restored to operation.
AUTOMATIC BRAKE ADJUSTER VALVE
Tests are not required on the individual adjuster
valve parts. After disassembly, cleaning, inspection,
repair or parts replacement, and complete reassembly
have been accomplished, perform a bench test to
determine whether the brake adjuster valve satisfies the
required minimum specifications.
The brake adjuster valve should be disassembled in
accordance with instructions contained in the MIM
and/or 03 manual. Check the safety wiring before
disassembly to expedite rewiring after reassembly.
Clean all parts except the nylon insert and O-rings
with P-D-680 cleaning solvent. The insert and O-rings
will normally be replaced upon each disassembly of the
valve. Dry parts with dry, clean, filtered, compressed air.
Do not inhale solvent vapors or direct
compressed air against the skin. Failure to
observe proper safety precautions could
result in injury to personnel.
Perform inspections under a strong light and with
magnification. Inspect all threads for crossed, filled, or
stripped conditions. Inspect all parts for nicks, scratches,
scoring, corrosion, or other damage. Check all drilled
passages for obstructions.
Repair or Parts Replacement
Replace any part that is damaged or does not
function properly. During replacement and before actual
reassembly, lightly coat all parts with hydraulic
preservative fluid; assemble parts while they are wet.
Reassembly is essentially the reverse of dis-
assembly. Directions for reassembly are provided in the
MIM and/or 03 manual.
The bench test consists of a series of testsproof
pressure, thermal crack, shuttle valve opening
operation, shuttle valve closing operation, and leakage.
Perform these tests in the order listed on a test bench,
and not while they are installed in the aircraft. The test
bench used must be capable of supplying hydraulic fluid
filtered through a 3-micron filter at a maximum pressure
of 2,250 psi. Conduct the tests at a room temperature of
70° to 90°F and a fluid temperature of 70° to 110°F.
Before you start the test, bleed all air from the unit. After
completing the test, remove the valve from the bench.
Flush with hydraulic preservative fluid, drip-drain, and
plug the ports. The cure date of the oldest scaling device
should be rubber-stumped on the body of the valve, and
the unit togged with the date and results of the test.
To perform the proof pressure test, apply a hydro-
static proof pressure of 2,250 psi to the RET (return) port
with the BRAKE and PMV (power/manual valve) ports
interconnected. Apply this pressure twice and hold for a
2-minute period each time. There should be no evidence
of external leakage, failure, distortion, or permanent set.
Perform the thermal crack test by applying pressure
gradually to the BRAKE port with the RET and PMV
ports open until the valve cracks. The residual pressure
should not be less than 27 psi. Again, gradually increase
pressure at the BRAKE port until the valve cracks. The
cracking pressure should be between 30 and 37 psi.
There should be no leakage from the PMV port.
NOTE: During piston travel a volume of fluid
will be displaced through the PMV port. Only
the portion of displaced fluid that exceeds 10
cubic centimeters should be considered as
leakage. No RET port fluid displacement
should be considered leakage.