LANCE
II SERVICE
MANUAL
The hydraulic pump
is a gear type
unit driven by a 14-volt
reversible motor
designed to
operate in a pressure
range of 2000 to 2500 psi. To prevent
excessive buildup of pressure in
the hydraulic system due to expansion, a thermal relief valve is incorporated in the pump.
This relief valve will
open at 2250 250 psi and allow fluid
to flow into the reservoir. Other
valves in the pump,
channel fluid to the proper outlet during
retraction or extension of 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 pressure refer to Table
VI-I.)
Also in the system is a by-pass or free-fall valve that allows the gear to drop should a
malfunction in the pump system occur.
To prevent the gear from extending
too fast, there is
a special restrictor
nipple on the main gear retraction line.
The valve is controlled manually
or by a gear back-up extension
device that is operated by a pressure
sensing device which
lowers the gear regardless of gear
selector handle position, depending
upon airspeed and
engine
power (propeller slipstream). Gear
extension occurs even if the selector
is in the up
position, at airspeeds below approximately 103 KIAS with engine power off. The device
also prevents
the gear from retracting at airspeeds
below approximately 81 KIAS at sea level
with full power, though the selector switch may be in the up position. This speed increases
with
reduced power and/or increased 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. Manual
override of the
device is provided
by an emergency
gear lever located between the
front seats to the right of the
flap handle.
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 lever,
when held in the raised position,
can be used to override the system,
and gear position is
controlled by the 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 latch allows the emergency extension lever to be retained in the up
override position. The latch is disengaged by pulling up on the extension lever. The lever
includes a centering device to return the handle to neutral, when not latched in override. An
auto extension off light is mounted below the gear selector switch, and flashes to indicate
whenever the
latch is in use. The auto extension
off light is controlled by a switch
and
flasher
mounted behind the
instrument panel.
For a description of the landing
gear and electrical switches, refer
to Section VII,
Landing Gear
and Brake System.
SEE
CAUTION
NOTE
ON GRID
1H18
Issued:
1/3/78
HYDRAULIC
SYSTEM
1H15
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