Hydraulic System Information - Piper Navajo Chieftain PA-31-350 Service Manual

NAVAJO CHIEFTAIN SERVICE MANUAL
SECTION VI
HYDRAULIC SYSTEM
6-1. INTRODUCTION.
The hydraulic system components covered in this section consist of landing gear
actuating cylinders. hydraulic lines, filters, hand pump and power pack. The brake system, although
hydraulically operated. is not included in this section as it has its own hydraulic system independent of the
power pack. The brake system along with landing gear is covered in Section VII of this manual.
This section also 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: Principles of Operation.
for a basic understanding of the system; Troubleshooting. for a methodical approach in locating the difficulty:
Corrective Maintenance. for removal. repair and installation of components: and Adjustments and Tests. 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.)
6-2. DESCRIPTION AND PRINCIPLES OF OPERATION. The hydraulic power pack is located in the
fuselage nose section just aft of the nose baggage compartment, and is operated by a selector lever. in the shape
of a wheel mounted to the right of the left control column. The power pack contains the system reservoir and
assorted valves which control the system operation. The power pack works in conjunction with various
electrical switches and solenoid valves to perform the desired sequences of operation as selected by the control
lever in the cockpit. Movement of the selector lever operates a control arm on the power pack through the use
of a flexible cable assembly and connecting arms. A solenoid operated lock is located behind the instrument
panel as part of the selector assembly to prevent the lever from being moved to the up position while the
airplane is on the ground. This solenoid is spring-loaded to the locked position and activated by an anti-
retraction (squat) switch mounted on the left main gear, upper torque link. The anti-retraction switch will
also sound a warning horn if the selector lever is moved to the gear up position while the aircraft is on the
ground and the master switch is ON. If the selector handle can be moved to the up position with the airplane
on the ground. it is an indication of an improperly adjusted selector mechanism or the anti-retraction system
is inoperative. The anti-retraction switch is actuated by the last .250 inch of oleo extension. When the selector
is moved to either the up or down position, it is locked in place by action of the handle release valve at the
power pack. acting against the release mechanism detent. The handle will remain in this position until it is
manually released or until fluid pressure in the actuator and lock release reaches its designed pressure. (Refer
to Table VI-I or Vl-ll.) At this time, the pressure forces the plunger in the lock release down, allowing the
lever to return to UP or DOWN neutral position. An electrically operated door solenoid valve located in the
power pack will position itself in the door (main inboard gear doors) open position when the selector lever is
placed in the up or down position with the master switch on: this valve is spring-loaded in the open position
and requires electrical current to remain in the closed position. In the event of electrical failure, the valve will
position itself in the open position and allow the doors to open when the selector lever is actuated and
hydraulic pressure routed through the system.
Revised:
10/5/83
2A12
HYDRAULIC SYSTEM
2A 12