Piper ARROW III, Руководство по обслуживанию

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Also in the system is a bypass or free-fall valve that allows the gear to drop should a malfunction in the
pump circuit occur. To prevent the gear from extending too fast, there is a special restrictor fitting on the side
of the valve. If your particular hydraulic system has the gear back-up extension device operation (refer to Piper
Service Bulletin 886A), this valve will operate one of two ways. First, manually by pushing the emergency
gear lever located on the forward center floor console between the front seats to the left of the flap handle, to
“Emergency Down” position. This method is the only way that the gear can be extended in an emergency if
you have complied with Piper Service Bulletin 886A. The second way of operating the free-fall valve is that if
you have not complied with Piper Service Bulletin 886A and opted to keep your gear back-up extension
system operational, the first method will apply, along with the operation of a pressure sensing device
incorporated in the back-up extension system. This pressure sensing device incorporated in the gear back-up
extension system which lowers the gear regardless of gear selector handle position, depends upon airspeed and
engine power (propeller slipstream). Gear extension occurs even if the selector is in the up position, at airspeed
below approximately 103 KIAS for the PA-28R-201T or 95 EUAS for PA-28R-201 with engine idled or in
power off. The device also prevents the gear from retracting at airspeed below approximately 78 KIAS for PA-
28R-201T or 75 KIAS for PA-28R-201 with full power, though the selector switch may be in the up position.
This speed increases with reduced power and/or increases altitude. The sensing device operation is controlled
by a differential air pressure across a flexible diaphragm which is mechanically linked to the hydraulic valve
and an electrical switch which actuates the pump motor. A high pressure and static air source for actuating the
diaphragm is provided in a mast mounted on the left side of the fuselage above the wing.
The emergency gear lever, used for emergency extension of the gear, manually releases hydraulic pressure
to permit the gear to “free-fall” with spring assistance on the nose gear. The lever must be held in the
downward position for emergency extension. This same level when held in the up position, can be used to
override the system, and gear position is controlled by the gear selector switch regardless of airspeed power
combinations. The lever must also be held in the raised position when hydraulic system operational checks are
being conducted. An override lock allows the emergency extension lever to be locked in the up override
position. A warning light is mounted below the gear selector lever and flashes to indicate whenever the lock is
in use. The lock is disengaged by pulling up on the extension lever.
For a description of the landing gear and electrical switches, refer to Section VII, Landing Gear and Brake
System.
6-3. TROUBLESHOOTING. Malfunctions of the hydraulic system obviously will result in failure of the
landing gear to operate properly. When problems occur, jack the airplane up (refer to Jacking, Section II) and
then proceed to determine the extent of the problem. Generally, hydraulic system problems fall into two types;
problems involving the hydraulic supplying system and problems in the landing gear hydraulic system. Table
VI-III at the back of this section, lists the problems which may be encountered and their probable cause and
suggestions to remedy the problem involved. A hydraulic system operational check may be conducted using
Figure 6-1 or 6-2. When the problem has been recognized, the first step in troubleshooting is to isolate the
cause. Hydraulic system problems are not always traceable to one cause. It is possible that a malfunction may
result of more than one difficulty within the system. Starting first with the obvious and most probable reasons
for the problem, check each possibly in turn and by process of elimination, isolate the problems.
Revised: 2/13/89
1H7
* CHEROKEE ARROW III SERVICE MANUAL
HYDRAULIC SYSTEM