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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 B.  The door-operated sequence valve controls flow of hydraulic fluid to the uplock actuator, the downlock actuator, and the main gear actuator. It is located on the outboard wall of the body gear wheel well, and is actuated by linkage attached to the aft end of the outboard door. During landing gear retraction, the right body gear door operated sequence valve, port UPc also controls flow of hydraulic fluid to pressure operated source selector valve 1, port C3. This is part of the gear retract braking sequence. Identical door-operated sequence valves are used in the nose gear and wing gear systems as well as the body gear system.
 C.  The downlock-operated sequence valve controls the flow of hydraulic fluid to the open side of the door actuator and is hydraulically interconnected to the uplock-operated sequence valve. The downlock-operated sequence valve is mounted at the top of the side strut and is operated by a striker plate attached to the strut. An identical downlock-operated sequence valve is used in the wing gear system.
 D.  The uplock-operated sequence valve controls the flow of hydraulic fluid to the closed side of the gear door actuator and is hydraulically interconnected to the downlock-operated sequence valve. The uplock-operated sequence valve is mounted on the side of the uplock mechanism. An identical uplock-operated sequence valve is used in the wing gear system.
 4.  Body Gear Uplock Mechanism (Fig. 5)
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 A.  The body gear uplock mechanism serves to positively lock the body gear in the up position. The lock consists of a hook, a hydraulic actuator, an electrical actuator, bungee cords, release cams and followers, plus a cable system to permit door release when the gear is lowered by alternate means. The uplock switch is mounted behind the hook and is operated by an arm working in conjunction with the hook. A tire bumper is located on station 1480 bulkhead to preclude damage or jamming of the gear truck against the uplock mechanism if strut air pressure is lost.
 5.  Body Gear Uplock Actuator
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 A.  The body gear uplock actuator operates by hydraulic fluid controlled by the door-operated sequence valve. It is mounted on the uplock mechanism. The actuator extends to unlock the hook and retracts to lock the hook. A schematic of this actuator is shown on figure 6.
 6.  Body Gear Downlock Actuator
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 A.  The body gear downlock actuator operates by hydraulic fluid controlled by the door-operated sequence valve. This actuator is mounted between the upper drag strut and the lower jury strut. It operates the jury strut which controls folding of the body gear drag strut (Fig. 1.) A cut-away of the body gear downlock actuator is shown in figure 6. The relief valve is shown exploded to clarify its operation. One of two rod end bleed plugs is also shown. You must open one of the bleed plugs, before the actuator is removed, to remove the remaining pressure from the retract side of the actuator.
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747-400 MAINTENANCE MANUAL
DOOR RELEASE

VIEW LOOKING DOWN
Body Gear Uplock Mechanism Figure 5
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
UNLOCK PORT  A 747-400 MAINTENANCE MANUAL CYLINDER 
PISTON 
RETAINER 
PISTON RING  SCRAPER 
O-RING AND SEAL 
BLEEDER PRESS. UNLOCK  HEAD END RESTRICTOR PLUG UPLOCK ACTUATOR 
PISTON 
PISTON SEPARABLE  BARREL CYLINDER  HOUSING ROD END 
　
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