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* Flow limiter in the up pressure line limits the flow to 8 gpm
(30 lpm) from the volume fuse to the frangible fitting and MLG
actuator
* Volume fuse in the up pressure line closes when the
hydraulic flow through the frangible fitting increases to 180-
250 cubic inches (3-4 liters). This stops the loss of fluid from
the hydraulic system.
MLG EXTENSION AND RETRACTION - FRANGIBLE FITTING
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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MLG EXTENSION AND RETRACTION - FRANGIBLE FITTING
MLG EXTENSION AND RETRACTION - FRANGIBLE FITTING
EFFECTIVITY
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737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
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THIS PAGE IS INTENTIONALLY LEFT BLANK
MLG EXTENSION AND RETRACTION - FRANGIBLE FITTING
32-32-00
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BOEING PROPRIETARY - Copyright#- Unpublished Work - See title page for details.
737-600/700/800/900 AIRCRAFT MAINTENANCE MANUAL
General
The extension and retraction sequence is the same for the left
and the right main landing gear.
The MLG extension and retraction system includes these
hydraulic components:
* Main landing gear actuator
* Downlock actuator
* Uplock actuator
* Transfer cylinder
* Frangible fitting.
Extension
The landing gear selector valve supplies down pressure when
the landing gear lever moves to the down position.
Down pressure goes to the transfer cylinder. This sets the
piston in the transfer cylinder to move to the up side. This gives
a time delay to let the uplock actuator unlock the uplock
mechanism. The restrictor/check valve controls the transfer
cylinder rate.
Down pressure also goes to the uplock actuator. The uplock
actuator retracts and this unlocks the uplock mechanism.
The shimmy damper decreases main landing gear shimmy.
The shimmy damper connects to the return line between the
landing gear selector valve and the landing gear transfer valve.
See the MLG and doors section for more information about the
shimmy damper. (SECTION 32-10)
When the transfer cylinder piston comes to the end of the up
side, down pressure goes to the down side of the gear actuator.
The gear actuator applies an extension force on the main
landing gear and moves it down.
Down pressure goes to retract the downlock actuator. The
downlock actuator moves the downlock strut to the locked
position as the main landing gear extends.
Retraction
The landing gear selector valve supplies up pressure when the
landing gear lever moves to the up position.
A flow limiter in the up pressure line limits the flow to the main
landing gear actuator to 8 gpm (30 lpm). The flow limiter makes
sure hydraulic system pressure stays normal for other airplane
systems that also use hydraulic pressure. The flow limiter also
controls the transfer cylinder rate and the main landing gear
extension and retraction rate.
MLG EXTENSION AND RETRACTION - FUNCTIONAL DESCRIPTION
EFFECTIVITY
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Up pressure goes to the transfer cylinder. This sets the piston in
the transfer cylinder to move to the down side. This gives a time
delay to let the downlock actuator extend to unlock the
downlock strut.
Up pressure goes to the downlock actuator. The downlock
actuator extends and unlocks the downlock strut.
When the transfer cylinder piston comes to the end of the down
side, up pressure goes to the up side of the gear actuator. The
gear actuator applies a retraction force on the main landing
gear and moves it up.
As the gear uplock roller moves into the hook of the uplock
mechanism, the uplock mechanism moves to the locked
position. The uplock actuator does not get up pressure.
The frangible fitting removes up pressure from the main landing
gear actuator if a damaged, spinning tire moves into the main
landing gear wheel well. This prevents damage to components
in the wheel well. A volume fuse in the up pressure line closes
when the hydraulic flow from the frangible fitting increases to
180-250 cubic inches (3-4 liters). This prevents hydraulic fluid
loss if there is a leak in the system.
Up pressure also goes to the alternate and gear retract brake
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