stripped conditions. Inspect all parts for nicks,
NOTE: During piston travel a volume of fluid will
be displaced through the PMV port. Only the portion
scratches, scoring, corrosion, or other damage. Check
of displaced fluid that exceeds 10 cubic centimeters
all drilled passages for obstructions.
should be considered as leakage. No RET port fluid
Repair or Parts Replacement
displacement should be considered leakage.
This procedure completes the thermal crack test.
Replace any part that is damaged or does not
In preparation for the shuttle valve opening operation
function properly. During replacement and before
test that follows, block residual pressure in the
actual reassembly, lightly coat all parts with hydraulic
BRAKE port using a pressure gauge as the plug.
preservative fluid; assemble parts while they are wet.
With the RET port open and BRAKE port capped,
apply hand-pumped hydraulic pressure gradually to
Reassembly
the PMV port. There should be a simultaneous
R e a s s e m b l y i s e s s e n t i a l l y t h e r eve r s e o f
increase of BRAKE port pressure with PMV port
pressure. At a pressure of 60 to 80 psi in the PMV port,
disassembly. Directions for reassembly are provided in
pressure in the PMV port and BRAKE port should
the MIM and/or 03 manual.
become equal. A gradual increase in PMV port
pressure to 1,500 psi should result in a proportionate
Bench Test
increase in the BRAKE port pressure. Any
The bench test consists of a series of tests--proof
displacement at the RET port should not be considered
pressure, thermal crack, shuttle valve opening
leakage during this phase of the bench test.
operation, shuttle valve closing operation, and
The shuttle valve closing operation test begins
leakage. Perform these tests in the order listed on a test
with 1,500 psi from the previous phase still applied to
bench, and not while they are installed in the aircraft.
the PMV port. Reduce the pressure at the PMV port to
The test bench used must be capable of supplying
150 psi, and then rapidly to 0 psi. The closing
hydraulic fluid filtered through a 3-micron filter at a
operation is evidenced by the venting of hydraulic fluid
maximum pressure of 2,250 psi. Conduct the tests at a
from the RET port as PMV pressure decreases from 20
room temperature of 70 to 90F and a fluid
psi to 0 psi.
temperature of 70 to 110F. Before you start the test,
The final phase of the bench test is the test for
bleed all air from the unit. After completing the test,
leakage. This phase is started with 27-psi hydraulic
remove the valve from the bench. Flush with hydraulic
pressure trapped in the BRAKE port. There should be
preservative fluid, drip-drain, and plug the ports. The
no evidence of pressure decrease when it is measured
over a period of 3 minutes. Continue the test with the
cure date of the oldest sealing device should be
BRAKE port capped and the RET port of the valve in
rubber-stamped on the body of the valve, and the unit
an upright position. Fill the RET port cavity and a
tagged with the date and results of the test.
leakage measuring device with hydraulic fluid. Apply
To perform the proof pressure test, apply a
hand-pumped hydraulic pressure of 30 to 37 psi to the
hydrostatic proof pressure of 2,250 psi to the RET
PMV port. Leakage at the RET port must not exceed
(return) port with the BRAKE and PMV
0.5 cubic centimeter per minute. Immediately after
(power/manual valve) ports interconnected. Apply
application of pressure, measure the leakage for a
this pressure twice and hold for a 2-minute period each
3-minute period. Disregard volume displacement
time. There should be no evidence of external leakage,
because of shuttle valve transition if leakage is not in
failure, distortion, or permanent set.
excess of 0.5 cubic centimeter per minute. Increase the
pressure to 125 psi and maintain for a 3-minute period.
Perform the thermal crack test by applying
There should be no evidence of leakage. Further
pressure gradually to the BRAKE port with the RET
increase the pressure to 1,500 psi and maintain for
and PMV ports open until the valve cracks. The
another 3-minute period. There should be no leakage.
residual pressure should not be less than 27 psi. Again,
gradually increase pressure at the BRAKE port until
BRAKE SELECTOR VALVE
the valve cracks. The cracking pressure should be
between 30 and 37 psi. There should be no leakage
Repair o f t h e b r a k e s e l e c t o r va l v e a t t h e
from the PMV port.
intermediate level of maintenance is limited to the
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