Piper Navajo PA-31 Service Manual page 297

PIPER NAVAJO SERVICE MANUAL
SECTION VI
HYDRAULIC SYSTEM
6-1. INTRODUCTION. The hydraulic system components covered in this section consist of Power
Pack.
hand pump, actuating cylinders, hydraulic lines, filters and hydraulic pump. The brake
system, although
hydraulically operated, is not included in this section. The brake system along with landing
gear is covered
in Section VII.
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 an interconnecting rod mechanism for early airplanes
or flexible cable
assembly on later airplanes. 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 of an 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 a preset
pressure. 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 failures
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: 10/12/83
HYDRAULIC SYSTEM
2A15