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PIPER AIRCRAFT CORPORATION
SECTION 7
PA-31T2, CHEYENNE II XL
DESCRIPTION & OPERATION
7.17 HYDRAULIC SYSTEM
The hydraulic system consists of two hydraulic pumps, a power pack, an
emergency hand pump, actuating cylinders and filters. The hydraulic pumps
which supply the pressure required for gear operation are engine-driven. The
power pack is the central control unit for the hydraulic system. It comains
the valves, manifold, fluid reservoir, and necessary controls for operation of
the landing gear.
Fluid is taken from the reservoir by the pumps and is passed through a
filter to the power pack, which then directs the fluid to the appropriate
actuator, depending on the sequence and gear selector position.
The reservoir contains a stand pipe which retains sufficient fluid to
operate the emergency hand pump in case of a loss of fluid. The engine-
driven pumps are supplied through the standpipe; so ifthe fluid level is below
the standpipe, the only way to operate the gear is by using the hand pump.
A door solenoid valve is electrically operated and is spring-loaded to the
door open position. Should an electrical failure occur, the solenoid valve will
move to the door open position to allow the gear to be lowered either
normally or with the hand pump. For a more detailed description, refer to
the P A-31 T2 Service Manual.
To operate the gear, pull out the wheel shaped gear selector mounted on
the left instrument panel, and move it from the neutral position to the UP
landing gear or DOWN landing gear position. When the desired position of
the gear is obtained, the handle is forced back to the neutral position by a
spring. The hydraulic fluid then circulates freely between the pump and
control unit. Gear retraction or extension will occur normally in
approximately LO seconds.
NOTE
In the event of electrical failure or when the
battery master switch is OFF, the selector
handle will not return to neutral, the gear doors
will not close, and the gear down lights will not
illuminate.
ISSUED: APRIL 22, 1981
REPORT: 2272
7-13
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