NLG EXTENSION-RETRACTION -NLG LOCKING MECHANISM AND NLG LOCK ACTUATOR -FUNCTIONAL DESCRIPTION
EFFECTIVITY BEJ ALL 32-34-00
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NLG EXTENSION-RETRACTION -NLG-OPERATED SEQUENCE VALVE
Purpose
The NLG-operated sequence valve makes sure that the doors move only if the NLG is in the retracted or the extended position. It makes sure that the doors do not move if the NLG is in-transit.
Physical Description
The NLG-operated sequence valve is a three position valve. The positions are:
*
Gear up
*
Gear in transit
*
Gear down.
A linkage from the nose landing gear locking mechanism moves the sequence valve.
Location
The NLG-operated sequence valve is on the aft bulkhead in the nose wheel well.
EFFECTIVITY BEJ ALL 32-34-00
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NLG EXTENSION-RETRACTION -NLG-OPERATED SEQUENCE VALVE
EFFECTIVITY BEJ ALL 32-34-00
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NLG EXTENSION-RETRACTION -NLG DOOR ACTUATOR AND NLG DOOR-OPERATED SEQUENCE VALVE
Purpose
The NLG door actuator opens and closes the NLG forward doors. A lock in the actuator holds the doors closed.
The NLG door-operated sequence valve controls the hydraulic flow to the NLG lock and retract actuators. This makes sure the NLG extends or retracts only when the NLG doors are open.
Physical Description
The NLG door actuator is a two-position hydraulic actuator. The actuator extends to open the doors and retracts to close the doors.
Flow restrictors at the head and rod ends of the actuator control actuator speed.
An internal lock engages when the NLG doors close. During normal operation, hydraulic pressure to open the NLG doors unlocks this lock.
The NLG door-operated sequence valve is a two position valve -OPEN and CLOSED. The sequence valve moves to the OPEN position when the doors are four degrees from the fully open position. A linkage from a hinge on the left forward NLG door operates the sequence valve.
Location
The NLG door actuator is in the forward, left side of the nose wheel well. The head end of the actuator attaches to a bracket on the wheel well ceiling. The rod end attaches to a crank. The crank moves both forward doors through rods.
The NLG door-operated sequence valve is on the left NLG wheel well wall.
EFFECTIVITY BEJ ALL 32-34-00
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NLG EXTENSION-RETRACTION -NLG DOOR ACTUATOR AND NLG DOOR-OPERATED SEQUENCE VALVE
EFFECTIVITY BEJ ALL 32-34-00
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777 AIRCRAFT MAINTENANCE MANUAL
THIS PAGE IS INTENTIONALLY LEFT BLANK
32-34-00
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NLG EXTENSION-RETRACTION -RETRACTION SEQUENCE
Initial Position
These are the initial positions for NLG components:
*
NLG -DOWN AND LOCKED
*
NLG doors -CLOSED
*
NLG-operated sequence valve -GEAR DOWN
*
NLG door-operated sequence valve -CLOSED.
Control
When you select UP with the landing gear control lever, the NLG selector/bypass valve moves to the up position. Hydraulic pressure then goes to the retract lines.
Gear Unlocks -Doors Open
Hydraulic pressure goes to the NLG lock actuator. The actuator starts to retract to unlock the downlock.
Pressure also goes through the NLG-operated sequence valve to the NLG door actuator. The actuator extends and opens the forward doors.
Gear Retracts
When the doors are almost fully open, the NLG door-operated sequence valve moves to OPEN. Pressure then goes to the NLG retract actuator and the NLG starts to retract.
EFFECTIVITY
BEJ ALL
After the NLG starts to retract, the NLG-operated sequence valve moves to the GEAR IN TRANSIT position. This keeps pressure on the open side of the door actuator. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：777 AMM 飞机维护手册 起落架 Landing Gear(21)
