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Downlock Actuator (Fig. 3)
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 (1)  The downlock actuator is also a hydraulic piston-type actuator that operates hydraulically in two directions. This actuator does not snub internally. The downlock actuator moves the downlock links to let the landing gear retract and also helps the downlock springs lock the downlock links when the landing gear extends. The actuator is installed on the upper downlock link. The head end attaches to the downlock spindle, and the rod end attaches to the upper downlock link near the apex of the downlock links.
Uplock Actuator (Fig. 4)
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 (1)  The uplock actuator is a hydraulic piston-type actuator that operates hydraulically in one direction. This actuator applies the force to move the uplock hook to release the main landing gear and let it extend. The actuator is installed on the uplock assembly on the outboard fairing of the wheel well for the main landing gear.
Door-Operated Gear Sequence Valve (Fig. 5)
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A

757 MAINTENANCE MANUAL
SEE A
DOOR ACTUATOR
MAIN
LANDING
GEAR
DOOR

CENTER HINGE SUPPORT BEAM
FWD
A
Door Actuator
Figure 2

 

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757
MAINTENANCE MANUAL

SEE A DOWNLOCK ACTUATOR
UPPER DOWNLOCK LINK
FWD
A
Downlock Actuator
Figure 3

 

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MAINTENANCE MANUAL

 (1)  
The door-operated gear sequence valve is a three-position valve. The valve controls the flow of hydraulic fluid to the downlock, uplock, and retract actuators. This valve controls the sequence of landing gear movement in relation to door position for the landing gear. The valve is connected to and operated by the door actuator. The valve is installed above the door actuator on the keel beam in the wheel well for the main landing gear.

 F.
Downlock-Operated Door Sequence Valve (Fig. 6)

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 (1)  The downlock-operated door sequence valve is a two-position valve. The valve controls the flow of hydraulic fluid to the door actuator. This valve is hydraulically connected to the uplock-operated sequence valve. The valve's primary function is to supply hydraulic pressure to the door actuator to close the door when the main landing gear is down and locked. The valve is installed on the jury brace, which is attached to the rear wing spar, just outboard of the upper downlock link. Valve position is operated by a target on the upper downlock link which engages a roller on the valve when the landing gear is down and locked.
UPLOCK-OPERATED
SEQUENCE VALVE

UPLOCK ACTUATOR
SEE A
UPLOCK ASSEMBLY INBD A
Uplock Mechanism Figure 4

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757 MAINTENANCE MANUAL
SEE A
DOOR-OPERATED GEAR SEQUENCE VALVE
DOOR
ACTUATOR

FWD A
Door-Operated Gear Sequence Valve Figure 5

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MAINTENANCE MANUAL

SEE A
FWD
SEQUENCE VALVE TARGET
DOWNLOCK-OPERATED
DOOR SEQUENCE VALVE UPPER DOWNLOCK LINK
A
Downlock-Operated Door Sequence ValveFigure 6

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MAINTENANCE MANUAL

 G. Uplock-Operated Sequence Valve (Fig. 4)
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 (1)  
The uplock-operated sequence valve is a two-position valve. It controls the flow of hydraulic fluid to the door actuator. This valve is hydraulically connected to the downlock-operated door sequence valve. Its primary function is to supply hydraulic pressure to the door actuator to open or close the door when the main landing gear is up and locked. A restrictor check valve installed in the hydraulic fitting in the line that connects this valve and the downlock-operated door sequence valve decreases the speed at which the door closes for safety. The uplock-operated sequence valve is installed on the uplock assembly on the outboard fairing of the wheel well for the main landing gear. The valve is connected, but not directly, to the uplock actuator and movement of the uplock actuator operates the valve position.

 H.
Truck Positioner Actuator (Fig. 7)
　
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本文鏈接地址：757 AMM 飛機維護手冊 起落架 CHAPTER 32 - LANDING GEAR 2(41)