Piper Cherokee LANCE, Service Manual

Page: 203 / 854

PIPER CHEROKEE SIX / LANCE SERVICE MANUAL
07/15/06 VA - HYDRAULIC SYSTEM
1I23
SECTION VA
HYDRAULIC SYSTEM
PA-32R-300
5A-l. INTRODUCTION. The PA-32R-300 hydraulic system components covered in this section consist of
the combination hydraulic pump and reservoir, gear back-up extender actuator assembly, actuating
cylinders and hydraulic lines. The brake system, although hydraulically operated, is not included in this
section as it has its own hydraulic system independent of the gear retraction system. The brake system
along with the landing gear and components is covered in Section VIA.
This section provides instructions for remedying difficulties which may arise in the operation of the
hydraulic system. The instructions are organized so that the mechanic can refer to: Description of the
System, for a basic understanding of the system; Troubleshooting, for a methodical approach in locating
difficulty; Corrective Maintenance, for the removal, repair and installation of components; and
Adjustments and Checks, for the operation of the repaired system.
CAUTION: PRIOR TO STARTING ANY INVESTIGATION OF THE HYDRAULIC SYSTEM,
PLACE THE AIRPLANE ON JACKS. (REFER TO JACKING, SECTION II.)
5A-2. DESCRIPTION. Hydraulic fluid to the landing gear actuating cylinders is supplied by an electrically
powered reversible pump located below the raised floor in the forward baggage compartment at station
45. A reservoir is also an integral part of the pump. The pump is controlled by a selector switch on the
instrument panel to the left of the control 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.
A pressure switch is installed on a cross fitting connected to the pump mount assembly. During
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. The switch will continue to hold the circuit open until pressure in the system drops when at
that time the pump will again operate to build up pressure as long as the gear selector handle is in the up
position. The down position of the selector does not affect the pressure switch. (For Specific Pressures
refer to Table VA-I.)
The hydraulic pump is a gear type unit driven by a 12 to 14 volt reversible motor designed to operate in a
pressure range as given in Table VA-I. A relief valve is incorporated in the pump, which when open
allows fluid to flow into the reservoir. Also incorporated in the system on earlier models is a primary
thermal relief valve which prevents excessive buildup of pressure in the hydraulic system due to
expansion. Other valves in the pump, channel fluid to the proper outlet during retraction or extension of
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. (For specific pressures refer to Table VA-I.)