Again out of the Sararatoga manual, the Hydraulic system, but it will be more or less the same system throughout the Piper range. REMEMBER ON BOTH OF MY REPLIES, parts locations and types as well as systems can and will vary. This will just give you an over view on how it works and you can use that to understand your systems from the information you have, for more ask your engineers, they will gladly show you the manual for your aircraft............ well I would.
This chapter provides an overview of the main hydraulic system which is used for landing gear extension
and retraction. Detailed information on the combination hydraulic pump and reservoir and the hydraulic
lines are provided herein. See 32-30-00 for detailed information on landing gear extension and retraction
components and operation.
The brake system, although hydraulically operated, is not included in Chapter 29 as it is entirely
independent of the gear retraction system. The brake system and its components are covered in Chapter 32.
A. Description
Hydraulic fluid is supplied to the landing gear actuating cylinders by an electrically powered,
reversible, pump located below the raised floor in the forward baggage compartment at F.S. 45. A
reservoir is also an integral part of the pump. The pump is controlled by the landing gear selector
switch located on the instrument panel to the left of the throttle quadrant. As the switch is placed in
either the up or down position, the pump directs fluid through the particular pressure line to each
individual actuating cylinder. As fluid pressure increases at one side of a cylinder piston, fluid at the
other side is directed back through the other line to the pump. Both lines serve either as pressure or
return passages depending on the rotation of the pump to retract or extend the gear. (Refer to
Figure 29-1.)
A pressure switch is installed on a cross fitting connected to the pump mount assembly. During
landing gear retraction the pressure switch is the primary means to shut down the pump. This switch
opens the electrical circuit to the pump solenoid when the gear fully retracts and the pressure in the
system increases to 1800 ± 100 psi. As long as the gear selector handle is in the up position the switch
will continue to hold the circuit open until system pressure drops to 200 to 400 psi. At that time, the
pump will again operate to build up pressure to prevent the gear from free falling. The pressure switch
has no effect on the system when the gear selector is in the down position.
The hydraulic pump is a gear type unit, driven by a 28-volt reversible motor,
designed to operate in a pressure range of 2000 - 2500 psi.
To prevent excessivebuildup of pressure in the hydraulic system due to expansion, a thermal relief valve is incorporated in the pump.
The relief valve will open at 3000 ± 500 psi. Other
valves in the pump channel fluid to the proper outlet during retraction or extension of landing gear. A
shuttle valve located in the base of the pump allows fluid displaced by the cylinder pistons to return to
the reservoir without back-pressure. (Refer to Figure 29-1 and Chart 2901for specific pressures.)
A by-pass or free-fall valve allows the gear to drop should a malfunction in the pump system occur.
This valve is manually controlled by the Emergency Gear Extension Knob, located on the instrument
panel, below the gear selection switch. A special restrictor nipple on the main gear retraction line
prevents the gear from extending too fast.
Pulling the emergency gear extension knob out manually releases hydraulic pressure, permitting the
gear to free-fall, with spring assistance on the nose gear.
How's that for an answer 