(g)  
Make sure that there are no pressure pulses in the down line hoses.

 (h)  
Move the control lever for the landing gear to DOWN.

 (i)  
Make sure that there are no pressure pulses in the down line hoses. Open the isolation valves.

 NOTE: Install the lockwire on the handles in the open
____
 position.

 CAUTION: MAKE SURE THE VALVE HANDLE IS IN THE POSITION AS
_______ SHOWN WITH THE VALVE OPEN. IF THE POSITION IS DIFFERENT, REPLACE THE INCORRECT VALVE HANDLE ASSEMBLY. THE GEAR WILL NOT RETRACT WITH THE VALVE IN THE CLOSED POSITION.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH ISOLATION VALVES ú

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A 737-300/400/500MAINTENANCE MANUAL
 (j) (k)  Install the handle stop bracket.Tighten the nuts with your finger.
 NOTE:____ Install the cotter pins.
 (l)  Decrease the pressure on the hydraulic system A.

 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH ISOLATION VALVES ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 NOSE GEAR EXTENSION AND RETRACTION - DESCRIPTION AND OPERATION
______________________________________________________________
 1.  General_______
 A.  The nose gear retraction and extension system raises and lowers the nose landing gear (Fig. 1). The gear retracts or extends simultaneously with the main gear when the landing gear control handle is moved into the UP or DN detent. A nose gear actuator applies the force necessary to raise or lower the gear. The nose gear actuator is attached to airplane structure forward and above the gear and to the lower end of the upper drag brace. A nose gear lock strut assembly, driven by an actuator and held in position by spring bungees, positively locks the gear in up or down position. The lock strut consists of a lock link and lock brace assembly located between the aft bulkhead and the upper drag brace. The lock actuator is mounted on the aft bulkhead between structure and an extension on the aft end of the lock brace. The spring bungees consist of two tension springs, one on each side of the lock brace. Bungees are connected to lugs on the lock link and at the lock brace pivot point on structure.
 2.  Nose Gear Actuator__________________
 A.  The nose gear actuator converts hydraulic pressure to the mechanical force required to raise or lower the nose gear. The actuator is a hydraulic piston type with snubbing action to slow movement when limits of travel are approached (Fig. 2). The cylinder head of the actuator is attached to a heavy bracket in the wheel well ceiling. The piston rod is attached to the upper drag brace. Hydraulic fluid is directed to both ends of the hydraulic cylinder through flexible hoses.
 B.  The nose gear actuator restricts the rate of extension and retraction of the gear just as the gear approaches the up or the down position. Snubbing effect is obtained by the action of a spring loaded sliding valve snubbing assembly. After the actuator has extended 0.65 inch, the snubbing valve opens and hydraulic flow is unrestricted. When the piston is one inch from the fully extended position, a stop on the piston contacts the snubber valve sleeve. Further movement of the piston pulls the sleeve against a compression spring to close ports. During the remainder of piston travel, hydraulic flow must pass through a diminishing number of holes. The increasing restriction to hydraulic flow steadily slows the actuator extension rate until the piston reaches the end of travel. The sequence repeats in reverse when the actuator retracts.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
NOSE GEAR ACTUATOR 
　
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