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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 Chart 2901. To prevent excessive buildup of pressure in the hydraulic system due to expansion, a thermal relief valve is incorporated in the pump. The pump’s relief valve opens at 3000 ± 200 to 300 psi. Other valves in the pump channel fluid to the proper outlet during retraction or extension of the 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 Chart 2901.)
Also in the system is a bypass or free-fall valve, operated by the emergency gear release knob, that releases hydraulic pressure to permit the gear to free fall, with spring assistance on the nose gear, should a malfunction in the pump system occur. The knob must be pulled out for emergency extension. To prevent the gear from extending too fast, there is a special restriction elbow on the nose gear retraction line. The knob must be pushed in when the hydraulic system operational checks are being conducted. The emergency gear knob is located on the instrument panel to the left of the control quadrants.
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AIRPLANE MAINTENANCE MANUAL

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THE NEW PIPER AIRCRAFT, INC.
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AIRPLANE MAINTENANCE MANUAL

— CAUTION —
TO PREVENT THE BUILDUP OF UNNECESSARY PRESSURE ON THE ACTUATING CYLINDERS AND CONNECTING HYDRAULIC LINES, WHEN THE GEAR IS RAISED OR LOWERED MANUALLY WITH THE AIRPLANE ON JACKS, PULL THE EMERGENCY GEAR RELEASE KNOB OUT. FAILURE TO COMPLY WITH THIS PROCEDURE COULD RESULT IN THE BUILDUP OF SUFFICIENT PRESSURE TO UNLOCK THE DOWN LOCK, ALLOWING THE GEAR TO COLLAPSE WHEN THE WING JACKS ARE REMOVED. PRIOR TO REMOVING THE AIRPLANE FROM THE JACKS, PUSH THE EMERGENCY EXTENSION KNOB IN, TURN THE MASTER SWITCH ON, AND SELECT GEAR DOWN. OBSERVE THAT ALL THREE GREEN LIGHTS ARE ENERGIZED, INDICATING THAT THE LANDING GEARS ARE DOWN AND LOCKED. TURN THE MASTER SWITCH OFF.
TROUBLESHOOTING.
If trouble develops in the landing gear, place the airplane on jacks (refer to Jacking, 7-10-00), and proceed to find the cause of the trouble. A hydraulic system operational check may be conducted using Figures 1 or 2 and the Landing Gear Retraction System Functional Test, 32-30-00. When the trouble has been recognized, the first step is to isolate the cause. After isolation of a particular cause or problem, refer to the individual Chapter pertaining to that subject matter, i.e. Landing Gear: Chapter 32.
Hydraulic system troubles are not always traceable to one cause. A malfunction may be the result of more than one trouble in the system. Start with the most obvious and most probable reasons for the trouble, check each possibility and, by process of elimination, isolate the fault.
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THE NEW PIPER AIRCRAFT, INC.
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AIRPLANE MAINTENANCE MANUAL

CHART 2901.  LEADING PARTICULARS, HYDRAULIC SYSTEM

HYDRAULIC PUMP  Piper P/N 481 879 - OILDYNE PUMP 
High Pressure Low Pressure Flow Rate @ 1000 psi Hydraulic Fluid Thermal Relief Valve Shuttle Valve Delivered Pressure  2400 ± 200 psi 600 ± 200 psi 60 cu. in. per min. MIL-H-5606 3000 + 300 / -200 psi 400 - 800 psi 
Pressure Switch Open (OFF) Pressure Close (ON) Pressure  1800 ± 100 psi 300 ± 100 psi 
Electrical Characteristics Voltage Rotation Polarity Operating Current Operating Time Overload Protection Automatic Reset Time Location, Automatic Reset  14 VDC Reversible Negative ground 18 amps, max at 14 volts(both rotations) 5 - 10 sec. (current load = 100 amps @ 77° F) Thermal circuit breaker 12 seconds, max. Commutator end head of motor 

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AIRPLANE MAINTENANCE MANUAL

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MAIN.

— WARNING —
FAILURE TO CONSULT APPLICABLE VENDOR PUBLICATION(S), WHEN SERVICING OR INSPECTING VENDOR EQUIPMENT INSTALLED IN PIPER AIRCRAFT, MAY RENDER THE AIRCRAFT UNAIRWORTHY. (SEE INTRODUCTION - SUPPLEMENTARY PUBLICATIONS.)
HYDRAULIC PUMP.
— Note — No repair is authorized of the Oildyne Hydraulic Pump. REMOVAL OF HYDRAULIC PUMP (Refer to Figure 29-2, Sheet 1 of 2)
The hydraulic pump with reservoir incorporated is located in the aft section of the fuselage between stations 156 and 191. Access to the pump is through the access panel in the baggage compartment.
　
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