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LANDING GEAR CONTROL SYSTEM - LANDING GEAR TRANSFER VALVE - FUNCTIONAL DESCRIPTION - ELECTRICAL
EFFECTIVITY
GUN ALL 32-31-00
Page 19
D633A101-GUN Feb 10/2003
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
32-31-00-009
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LANDING GEAR CONTROL SYSTEM - LANDING GEAR TRANSFER VALVE - FUNCTIONAL DESCRIPTION - ELECTRICAL
32-31-00
Page 20
D633A101-GUN Oct 10/2002
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
General
Hydraulic system A normally supplies pressure for landing gear
extension and retraction. Hydraulic system B supplies pressure
for retraction only, through the landing gear transfer valve.
Landing Gear Transfer Valve
The landing gear transfer valve has these components:
* Solenoid valve
* Slide valve
* Position switch.
When the solenoid valve does not receive a signal, pressure
from hydraulic system A moves the slide valve to the normal
position. In the normal position, the landing gear transfer valve
sends hydraulic system A pressure to the landing gear selector
valve.
When the solenoid valve receives a signal from the proximity
switch electronics unit (PSEU), the solenoid valve opens. This
sends hydraulic system B pressure to move the slide valve to
the alternate position. In the alternate position, the landing gear
transfer valve sends hydraulic system B pressure to the landing
gear selector valve.
When the slide valve moves to the alternate position, the
position switch on the landing gear transfer valve closes. This
sends a ground to the built-in-test equipment (BITE) of the
PSEU.
See the Air/Ground System Section for more information about
the PSEU. (SECTION 32-09)
Landing Gear Selector Valve
The landing gear lever operates the landing gear selector
valve. These are the three positions of the landing gear selector
valve:
* UP (retract)
* OFF
* DOWN (extend).
The landing gear selector valve has these components:
* Slide valve
* Manual extend solenoid valve
* Bypass valve.
When you move the landing gear control lever to the OFF
position, the selector valve moves to the off position. Extension
and retraction components do not pressurize.
LANDING GEAR CONTROL SYSTEM - FUNCTIONAL DESCRIPTION - HYDRAULIC
EFFECTIVITY
GUN ALL 32-31-00
Page 21
D633A101-GUN Oct 10/2002
BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
32-31-00-010
When the landing gear control lever moves to the DOWN
position, the selector valve moves to the down position. Down
pressure goes to the landing gear components for landing gear
extension. Down pressure also moves the bypass valve to the
normal position.
When the landing gear control lever moves to the UP position,
the selector valve moves to the up position. Up pressure goes
through the bypass valve to the landing gear components for
landing gear retraction.
The manual extend solenoid valve has a normal position and an
alternate position. When the coil on the manual extend solenoid
valve does not receive a signal, a spring moves the manual
extend solenoid valve to the normal position.
The bypass valve has a normal and a bypass position. Pressure
from the slide valve or the manual extend solenoid valve
operates the bypass valve. During normal landing gear
operation, the bypass valve moves to the normal position.
When you open the manual extension access door, the manual
extend solenoid valve energizes. The manual extend solenoid
valve moves to the alternate position. When the manual extend
solenoid valve moves to the alternate position, pressure goes to
move the bypass valve to the bypass position.
When the bypass valve moves to the bypass position, up
pressure does not go to the landing gear. Also, the bypass
valve connects the landing gear retraction up pressure lines to
the hydraulic system return. This lets the manual extension
system extend the gear if the slide valve of the selector valve
jams in the up position.
Nose Wheel Steering
The pressure for nose wheel steering comes from the nose
landing gear extension pressure only. Hydraulic system A
normally supplies pressure to the nose wheel steering system.
When you move the alternate nose wheel steering switch on the
P1 panel to the ALT position, the landing gear transfer valve
moves to the alternate position. When you operate the alternate
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