32-33-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 6.  Nose Gear Modular Package
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 A.  The nose gear modular package contains all the valves required to modify hydraulic flow directed to the nose gear retraction and lock actuators (Fig. 5). Two flow limiting valves in the up line to the nose gear actuator are arranged to limit the rate of flow entering or leaving the up port of the actuator. The flow limiting valves prevent pressure surges in the system from varying the rate of actuator movement between snubbing points. A priority valve and a two-way restrictor are installed in parallel in both the up and the down lines to the nose gear lock actuator. Fluid entering the lock actuator ports, either up or down, passes through a two-way restrictor valve unrestricted. Fluid leaving the ports is blocked off by a priority valve and must pass through a restrictor. Any pressure surges over 3500 psi are released by the priority valve. The valves in the modular package ensure smooth and accurate movement when raising or lowering the gear. The modular package is mounted in the left upper aft corner in the nose wheel well.
 7.  Nose Gear Hydraulic Fuse
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 A.  A volumetric hydraulic fuse is located in the gear up pressure line to the left of the system A hydraulic reservior in the ceiling of the main wheel well. The purpose of the fuse is to prevent loss of hydraulic fluid in the event of a leak downstream of the fuse. The fuse will shut off after 60 - 90 cubic inches of fluid have passed through. With normal forward and reverse flows, the fuse is self-resetting. If a trouble shoot of the fuse is needed, the removal of the fuse from the airplane is required.
UNLOCK PORT FROM GEAR UP,

SCRAPER
Nose Gear Lock Actuator Figure 4
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 8.  Transfer Cylinder_________________
 A.  The transfer cylinder momentarily equalizes hydraulic pressure on either side of the nose gear actuator piston at the start of each extension or retraction cycle to relieve the gear of the actuator force until the lock is released. The cylinder contains a piston, two springs, and two spring retainers (Fig. 6). One end of the cylinder is connected to the down line. The other end is connected to the up line of the nose gear actuator. At the end of the gear retraction or extension, the cylinder spring retainer is bottomed on either side of the cylinder. When the control handle is moved to UP or DN for gear operation, pressure is directed to one side of the nose gear actuator and the transfer cylinder. Piston movement directs pressure from the opposite side of the cylinder to the actuator. Therefore, momentarily, system pressure exists on both sides of the actuator piston and actuator force is neutralized. During the neutral force period, the lock actuator unlocks the gear and starts the lock brace assembly folding. When the spring retainer bottoms, the counter pressure drops on the return side of the nose gear actuator and gear extension or retraction proceeds. After the spring retainer has bottomed and hydraulic pressure is off the line, further movement of the piston is available, acting against the spring tension. The extra piston movement is provided to damp out pressure surges generated in the system and so prevent pressure fluctuations from reaching the lock actuator and possibly unlocking the gear. The cylinder is mounted on the forward bulkhead in the wheel well.
TO GEAR TO LOCK
TO LOCK ACTUATOR
TWO WAY FLOW
RESTRICTOR LIMITER
PRIORITY VALVE
VENT
FLOW
LIMITER

LINE
ARROWS SHOW FLOW THROUGH MODULAR PACKAGE WHEN GEAR IS EXTENDING
Nose Gear Modular Package Schematic Figure 5
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
 9.  Nose Gear Door Linkage
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