MLG EXTENSION-RETRACTION -MLG TRUCK POSITIONER ACTUATOR -FUNCTIONAL DESCRIPTION
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MLG EXTENSION-RETRACTION -MLG TRUCK POSITIONER ACTUATOR FUSES
Purpose
The MLG truck positioner actuator fuses prevent loss of center hydraulic system fluid if there is a leak in the hydraulic lines to the MLG truck positioner actuator.
There are fuses in the tilt and stow hydraulic pressure lines that go to each MLG truck positioner actuator.
Location
The truck positioner actuator fuses are above the MLG truck near the main landing gear beam.
Training Information Point
The fuses close if 60 -90 cubic inches of hydraulic fluid go through the fuse at a minimum rate of 0.1 gallons per minute.
The fuses reset automatically when the pressure difference across the fuse is five psi or less.
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MLG EXTENSION-RETRACTION -MLG TRUCK POSITIONER ACTUATOR FUSES
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MLG EXTENSION -RETRACTION -MLG DOOR PRIORITY/RELIEF VALVE
Purpose
The MLG priority/relief valve limits pressure to the MLG door actuator during gear retraction. This makes sure sufficient pressure goes to the truck positioner actuator to move the truck to the STOW position before the gear enters the wheel well.
Location
A MLG door priority relief valve is on the ceiling of each MLG wheel well.
Functional Description
The MLG priority/relief valve operates by pressure. When pressure upstream of the valve goes below 2000 psi, the valve limits door open pressure to the MLG door actuator.
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MLG EXTENSION -RETRACTION -MLG DOOR PRIORITY/RELIEF VALVE
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777 AIRCRAFT MAINTENANCE MANUAL
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MLG EXTENSION-RETRACTION -RETRACTION SEQUENCE
General
MLG retraction is the same for both left and right main gears.
These are the start positions:
*
MLG -DOWN and LOCKED
*
MLG door -CLOSED and LOCKED
*
MLG truck positioner actuator -TILT
*
MLG drag brace-operated sequence valve -DOWN
*
MLG uplock-operated sequence valve -UNLOCKED
*
MLG door-operated sequence valve -NOT OPEN.
Control
When you move the landing gear lever to the UP position, the MLG selector/bypass valve moves to the UP position. Hydraulic pressure then goes to the retract lines.
Gear Unlock -Truck Tilt
The pressure goes to the MLG drag brace and MLG side brace downlock actuators. These actuators start to retract to unlock the gear downlocks.
Pressure also goes through the MLG drag brace-operated sequence valve and the MLG uplock-operated sequence valve. This pressure extends the MLG truck positioner actuator to the STOW position.
EFFECTIVITY
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Door Opens
Pressure through the sequence valves also retracts the MLG door lock actuator to unlock the main gear door. The MLG door actuator gets extend pressure through the MLG door priority/ relief valve. The MLG door starts to open.
Gear Retracts
When the MLG door is almost all the way open, the MLG door-operated sequence valve moves to OPEN. Pressure then goes to the MLG retract actuator to retract the gear.
When the gear starts to retract, the MLG drag brace-operated sequence valve moves to the NOT DOWN position.
As the MLG goes into the wheel well, a roller on the landing gear strut moves the MLG uplock mechanism to the LOCKED position. This moves MLG uplock-operated sequence valve to the locked position.
This removes pressure from the MLG truck positioner actuator. Pressure trapped in the MLG truck positioner actuator keeps the MLG truck in the STOW position.
Pressure then goes to the MLG uplock actuator to make sure the MLG uplock mechanism locks.
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