Piper ARROW III Service Manual Download

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SECTION VI

HYDRAULIC SYSTEM

6-1. INTRODUCTION. The hydraulic system components covered in this section consist of the combination
hydraulic pump and reservoir (both Prestolite and Oildyne), gear back-up extender actuator assembly (if
operational), actuating cylinders and hydraulic lines. The brake system, although hydraulically operated, is not
included in this section because it incorporates its own hydraulic system which is independent of the gear
retraction system. The brake system along with the landing gear and components are covered in Section VII.

This section provides instructions for remedying problems 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 problems;
Corrective Maintenance, for the removal, repair and installation of components; Adjustments and Checks, for
the operation of the repaired system.

CAUTION

Prior to any investigation of the hydraulic system, properly place the
airplane on jacks. (Refer to Jacking, Section II.)

6-2. DESCRIPTION. Hydraulic fluid is supplied to the landing gear actuating cylinders by an electrically
powered reversible pump located aft of the baggage compartment at right side station 156.00. There are two
vendors that supply pumps that are incorporated in the PA-28R-201/201T airplane. One pump, which has been
installed in Piper airplanes for years is the Prestolite. The latest that has been installed, is the Oildyne. Both are
interchangeable, and are similar in that they both have reservoirs that are an integral part of the pump. Both
pumps are controlled by a selector handle located on the instrument panel to the left of the control quadrant. As
the handle is selected to either the up or down position, the pump directs fluid through a single line to a
manifold and from that manifold to each individual actuating cylinder. As fluid pressure increases at one side
of a cylinder piston, fluid at the opposite side is directed back through another manifold to the pump reservoir.
The two manifolds and their connecting lines serve either as pressure or return passages depending on the
rotation of the pump to retract or extend the gear.

On the manifold through which pressured fluid passes during gear retraction, there is located a pressure

switch which opens the electrical circuit to the pump solenoid when the gear fully retracts and pressure in the
system increases to 1800 plus or minus 100 psi. The switch will continue to hold the circuit open until pressure
in the system drops to 1500 plus or minus 100 psi, which at this point the pump will again operate to build up
the pressure as long as the gear selector handle is in the up position. The down position of the gear handle has
no effect on the pressure switch

The hydraulic pump is a gear type unit driven by a 14 volt reversible motor. To prevent excessive pressure

on the hydraulic system due to fluid expansion, there is a thermal relief valve incorporated in the Prestolite
pump that will open at 2250 plus or minus 250 psi, and the Oildyne pump at 3000 plus 300 or minus 200 psi,
thus allowing fluid to flow to the pump reservoir. Other valves in the pump system channel fluid to the proper
outlets during gear retraction or extension. In the base of the pump is a shuttle valve that allows fluid displaced
by the cylinder piston rods to return to the reservoir without back pressure. This shuttle valve has a delivery
pressure of 400 to 800 psi during the extension cycle.

Piper ARROW III, Service Manual

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