PRIORITY VALVE
VENT
FLOW LIMITER
TO MAIN ACTUATOR UP PORT
ARROWS SHOW FLOW THROUGH MODULAR PACKAGE WHEN GEAR IS EXTENDING

Main Gear Modular Package Schematic
Figure 6

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A 737-300/400/500MAINTENANCE MANUAL
 9.  Main Gear Isolation Valves (If installed)
__________________________
 A.  ON AIRPLANES WITH ISOLATION VALVES; The main gear isolation valves are provided to enable maintenance to be carried out on the landing gear and landing gear hydraulic components without depressurizing the hydraulic system. The valve consists of a dual unit in a modular package (Fig. 8). The valves are normally lockwired in the open position. The isolation valve modular package is mounted in the left wheel well.
 10. Main Gear Pressure Relief Valve (If Installed)
_______________________________
 A.  The retraction pressure relief valves are provided to enable the main gear actuator to retract smoothly without irractic motion due to excess weight of the landing gear brakes. The pressure relief valve is located above the right and left main gear trunnion attached between the main gear actuator and the check valve. The pressure relief valve consist of an alloy housing containing an adjustable spring-loaded poppet. The pressure relief valves are preset to restrict hydraulic flow at a specified pressure. Once the specified pressure is exceeded, the spring-loaded poppet will open and allow hydraulic fluid to flow until the pressure drops below the specified pressure. The spring-loaded poppet will then close and restrict flow.
PISTON RING SET PISTON CYLINDER

IN TRANSIT CONDITION

Main Gear Transfer Cylinder Schematic
Figure 7

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A
737-300/400/500MAINTENANCE MANUAL
 11. Operation (Fig. 9)_________
 A. Retraction
 (1)  When the control lever is moved to UP position, hydraulic pressure is then directed to the modular package and to the uplock actuator. After passing through the modular package, pressure reaches the up port of the main actuator and the uplock port of the downlock actuator. Flow to the main actuator is controlled by flow limiting valves and pressure relief valves. Flow to the downlock actuator is restricted. Flow from the downlock actuator is unrestricted. Therefore, the downlock actuator quickly unlocks the gear and starts the side strut folding before full pressure builds up in the main actuator (Fig. 9). When the gear retracts, the uplock actuator has locking pressure but stop links prevent the uplock hook from moving to locked position. On the final movement to full retraction, the uplock roller strikes a projection on the uplock hook; this triggers stop links to flip over and release the hook. The pressurized lock actuator then snaps the hook into final locked position. In the same movement, the stop links engage in locking detents to hold the hook in position.

GEAR  GEAR
PRESSURE
VALVE OPEN  VALVE CLOSED

Main Landing Gear Isolation Valve
Figure 8

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
C1 C2 C1 C2 C1 C2
UP LINE 
TO NOSE 
LANDING GEAR  DOWN LINE  DOWN PR  R  OFF  P  R  UP  P 
SELECTOR VALVE 
MAIN GEAR 
DAMPER 
MAIN GEAR 
MAIN GEAR  UPLOCK 
DOWNLOCK  ACTUATOR 
ACTUATOR 
CHECK 
VALVE 
FLOW 
LIMITER 

RELIEF
VALVE

R
3500
3500
　
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本文鏈接地址：737-300 400 500 AMM 飛機維護手冊 起落架 LANDING GEAR 2(68)