UPLOCK
DOWNLOCK ACTUATORENGAGED
DISENGAGED
DOWN

UP
BODY GEAR ACTUATOR
RETURN
INT DN UP
LOCK
UNLOCK
LEGEND:
CLOSE OPEN
HOOK
CLOSED

DOWNLOCK OPEN
ACTUATOR
OPEN
DOOR ACTUATOR
CLOSE Body Gear Hydraulic System Schematic Figure 9 (Sheet 4)
TO SECOND BODY GEAR
UP
BLOCKED
UP
PRESSURE

RETURN
DOWN
PRESSURE

SNUBBER
VALVE

U23266
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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 ALL  ú ú 02 Page 16 ú Jun 10/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 (4)  
When the gear is up and locked and DN is selected, hydraulic fluid is directed to the down port of the downlock-operated sequence valve. Since the gear is up, the downlock is disengaged which positions the sequence valve so that fluid is directed to the open side of the door actuator.

 (5)  
When the gear extends and locks down, the sequence valve is mechanically positioned to shut off fluid flow to the open side of the door actuator and to direct it through the uplock-operated sequence valve to the closed side of the door actuator which closes the gear doors. When gear UP is selected, fluid is directed to the sequence valve UP port. The sequence valve is in the downlock engaged position which directs fluid to the open side of the door actuator, thus opening the doors.

 (6)  
When the gear is down and locked, the flow thru the interconnect line from the downlock operated sequence valve is restricted to slow the door closing speed.

 (7)  
When the downlock actuator unlocks, the sequence valve moves to the downlock disengaged position; however, fluid is still directed to the open side of the door actuator as the gear is retracting. When the gear is up and locked, the uplock-operated sequence valve directs fluid to the closed side of the door actuator.

 (8)  
When the gear is up and locked and DN is selected, the uplock hook is closed. This positions the sequence valve so that fluid is directed to the open side of the door actuator. As the uplock actuator opens the gear up hook, allowing the gear to extend, the sequence valve is mechanically positioned to block fluid entering from the down port. However, the door actuator still remains in the open position due to fluid from the downlock sequence valve. When the gear is down and locked, fluid from the downlock-operated sequence valve is directed through the interconnecting line and through the uplock sequence valve to the close side of the door actuator and the doors close.

 (9)  
When gear UP is selected, the uplock hook is still in the open position which positions the valve so that fluid is directed to the open side of the door actuator where the valve remains until the gear is retracted and locked up. When the gear is locked up, the hook closes. This mechanically repositions the valve so that fluid is directed to the close side of the door actuator.

 (10)
 When the landing gear down cycle is initiated, the body gear actuator is pressurized to extend. Extension of the actuator piston causes the gear to rotate about the trunnion and extend. The downlock actuator is also pressurized, pulling the jury strut into the overcenter (locked) position preventing the drag strut from folding.

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 32-33-00
 ALL  ú ú 02 Page 17 ú Jun 10/92
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 (11)
 As the actuator retracts it retracts the gear, swinging it forward into the body gear wheel well. Upon initiation of the door retract cycle, the doors open. The door-operated sequence valve then directs fluid to the unlock side of the downlock actuator. The actuator extends pushing the jury strut across the overcenter position and starts the side strut folding. Retraction of the actuator pulls the jury strut into the overcenter locked position when the gear extends. (See figure 1.)
　
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