Main Gear Operating Sequence  500 
32-32-0  Figure 3 (Sheet 1)  May 15/67 
Page 6 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

500  Main Gear Operating Sequence 
May 15/67  Figure 3 (Sheet 2)  32-32-0 
Page 7 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

Main Gear Mechanism Schematic  500 
32-32-0 Page 8  Figure 4 (Sheet 1) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 15/67 

500  Main Gear Lock Mechanism Schematic 
May 15/67  Figure 4 (Sheet 2) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  32-32-0 Page 9 

6.  Main Gear Lock Springs
A.  The main gear lock springs are arranged to apply a load to hold the locks in either engaged or disengaged positions. Lock springs consist of tension springs, with one end attached to a fixed pivot point, and the other end to the appropriate lock mechanism. When locks operate, the spring ends attached to lock mechanism swing through an arc, the highest point of which is in line with the spring fixed pivot point. Therefore, an overcenter effect keeps locks in position, fully open or closed.
7.  Main Gear Modular Package
A.  The main gear modular package contains all the valves required to modify hydraulic flow directed to the main gear retraction and lock actuators (Fig. 6). Two flow limiting valves in the main gear actuator up line are arranged to limit the rate of flow entering or leaving the up port of the actuator. A priority valve and a flow-limiting valve are installed in parallel in the downlock actuator up line. A second pair of identical valves are installed in the uplock actuator down line. Each pair of valves controls the hydraulic flow leaving the respective lock actuators when retracting. Any pressure surges exceeding 3500 psi, when actuators are retracting, are released by the priority valve. The net effect of all the valves in the modular package ensures smooth, even, synchronized movements, of gear retraction and extension. A modular package is located in the wing root above each main gear.

Main Gear Lock Actuator  500 
32-32-0Page 10   Figure 5 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  May 15/67 

500  Main Gear Modular Package Schematic 
Feb 15/68  Figure 6  32-32-0 
Page 11 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

8.  Main Gear Transfer Cylinder
A.  The main gear transfer cylinder momentarily equalizes hydraulic pressure on both sides of the main gear actuator piston. Pressure is equalized at the start of each extension cycle to relieve gear of actuator force until the uplock is released. The transfer cylinder contains a piston, two springs and two spring retainers (Fig. 7). One end of the cylinder is connected to the DOWN line. The other end is connected to the UP line of main gear actuator. At the end of gear retraction, the cylinder spring retainer is bottomed on the DOWN side of transfer cylinder. When the control handle is moved to DN for gear extension, pressure is directed to the down side of main gear actuator. Pressure also enters the down side of transfer cylinder and displaces the piston. Piston movement directs pressure from the up side of cylinder to the up side of actuator. A flow-limiting valve in the main gear modular package delays the pressure loss to return. Therefore, momentarily, pressure exists on both sides of the actuator piston and actuator force is reversed. During the reversal period, the lock actuator unlocks the gear and starts the side strut folding. When the spring retainer bottoms, the counter pressure drops on the up side of the main gear actuator, and gear extension proceeds in the normal manner. After the spring retainer has bottomed and hydraulic pressure from a system is off the line, a 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 by landing impacts and so prevent pressure fluctuations from reaching the lock actuator and possibly unlocking the gear. The cylinder is symmetrical, with double springs, and may be installed either way in the system. The cylinder is mounted in the wing root on the main spar.

Main Gear Transfer Cylinder Schematic  500 
32-32-0  Figure 7  May 15/68 
Page 12 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 
　
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