Piper Navajo Chieftain PA-31-350 Service Manual page 286

NAVAJO CHIEFTAIN SERVICE MANUAL
The engine driven hydraulic pumps draw fluid from the power pack reservoir and pump it through the
system filters mounted on the engine side of the fire wall and check valves back to the pressure port of the
power pack. Within the power pack, fluid travels into the gear door solenoid valve and landing gear selector
pressure chamber. When the selector valve is in the neutral position, the fluid travels through the landing
gear selector valve back to the reservoir.
When the selector valve is moved either to the UP or DOWN position, it electrically actuates the door
solenoid valve to the open position, thus allowing fluid to flow through the door solenoid valve and opening
the doors. During the time the doors open, the gear priority valve remains closed as less pressure is required
to operate the doors. After the gear doors have opened, pressure continues to build up enough to allow the
priority valve to open and permit fluid to flow through the gear selector valve to the gear actuating
cylinders, thus allowing the gear to move to the up or down position.
After the gear has moved to the full up or down position, limit switches are actuated which cause the
electrically operated door solenoid valve to move to the closed door position, which allow the door
actuating cylinders to close the gear doors. When the doors have fully closed, pressure builds up in the time
delay valve operated by pressure in the closed door cylinders. The valve opens and allows fluid to flow to
the handle release valve, thus returning the selector lever to neutral. With the selector in neutral, fluid is
allowed to circulate back to the reservoir.
The main relief valve functions as a safety between the pump and selector valves. When the main relief
valve opens, fluid is directed back to the reservoir. The hand pump relief valve also serves as a secondary
relief valve. Valve operating pressures can be found in Table VI-I for Ozone Power Pack or Table VI-II for
Wiebel Tool Power Pack.
The thermal relief vent valve functions as a safety to relieve pressure due to thermal expansion in the
gear door actuating cylinders.
The hand pump serves as an emergency pump, should the engine driven pumps fail. The system check
valves prevent the fluid from backing up through the engine driven pumps into the reservoir. In the event of
severe leakage of the hydraulic fluid, the standpipe in the reservoir prevents the fluid level from dropping
below the emergency quantity required for the operation of the system by means of the hand pump. The
engine driven pumps are supplied with fluid through the standpipe, so that when the fluid level goes below
the top of the standpipe, no fluid will flow. Thus, even though the system may develop a break, and the
engine driven pumps continue to operate, devoiding the system of fluid, the standpipe insures enough fluid
in the system for hand pump operation.
In case of an electrical failure, the door solenoid valve will move to the door open position and remain
in that position.
Reissued: 9/23/80
HYDRAULIC SYSTEM
2A15