Checking Engine-Driven Hydraulic Pump Operation; Checking Powerpak Main Relief Valve - Piper APACHE PA-23-235 Service Manual

PIPER AZTEC SERVICE MANUAL
6-13. CHECKING
ENGINE-DRIVEN HYDRAULIC
PUMP(S)
OPERATION. To
determine the operational condition of the hydraulic system, the following checks may be
conducted to determine condition of the engine-driven hydraulic pump(s).
a. Start the left engine and allow it to warm up.
b. With the engine operating at 1200 RPM, move the landing gear selector lever to the
DOWN position. The engine-driven hydraulic pump should build up pressure in the system
and return the selector lever to the neutral position within a few seconds.
c. Should it be found that the selector lever is abnormally slow during the check, it can
be assumed that the hydraulic pump or powerpak is at fault.
d. To determine which of the two units is defective, proceed with the following steps:
1. Shut down the engine and select gear DOWN.
2. Operate the powerpak hand pump until the gear selector lever returns to the
neutral position.
3. If the time is shorter than the engine-driven time, it is an indication of a defective
engine-driven pump. (Refer to paragraph 6-27.)
4. If the time is approximately the same as the engine-driven time, it is an indication
that the powerpak is at fault and requires further checks to isolate the trouble. (Refer to
paragraph 6-16.)
e. On airplanes with Serial Nos. 27-7854051 and up, an engine-driven pump has also been
installed on the right engine. Check this pump by shutting down the left engine and repeating
the preceding steps with the right engine operating. Should it be found that the selector handle
is abnormally slow for one pump, but will return normally with the other pump, then it can be
assumed that the pump is at fault and it should be removed to determine the cause of the
malfunction.
6-14. CHECKING POWERPAK MAIN RELIEF VALVE. The cracking pressure that the
main relief valve opens within the powerpak may be determined as follows:
a. Connect a test unit in accordance with instructions given in paragraph 6-7.
b. Open the hydraulic test unit by-pass valve.
c. Hold the landing gear selector lever full DOWN.
d. Operate the test unit, and slowly close the by-pass valve, observing pressure build-up
and point at which the pressure stabilizes on test unit gauge. Stabilization indicates relief
valve setting. (Refer to Table VI-II for powerpak and its pressure requirement.)
e. The powerpak must be removed (refer to paragraph 6-38) and partially disassembled
to adjust the relief valve. (Refer to paragraph 6-61.)
f.
If no further checks are desired, remove the hydraulic test unit per instructions in
paragraph 6-8.
HYDRAULIC SYSTEM
2B12
Reissued: 2/18/81
2B12