8. Operation
A. When the captain or first officer depresses the brake pedals, the brake metering valves are opened and hydraulic fluid is directed to the brakes through antiskid valves and brake hydraulic fuses (Fig. 7). The intensity of pressure established in the brakes varies directly with the amount of pedal force maintained. Feel at the brake pedals depends on brake metering valve return spring, brake pressure diverted to oppose metering valve piston and brake pressure acting on head ends of piston in brake valve feel augmentation actuator. Depressing left or right brake pedals gives independent left or right brake operation on the main landing gear. When pedal force is reduced, fluid in the brakes is released to the hydraulic system return. Energy for brake operation in event of normal hydraulic system failure is stored in the brake accumulators. The accumulators are precharged with compressed air or nitrogen and contain sufficient energy for approximately three full brake applications.
B. When the automatic braking system is operating, the brake metering valves are bypassed and antiskid valves modulate brake pressure as required by the automatic braking system. Refer to 32-43-0 for automatic braking operation.
531 Main Gear Brake Swivel Assembly
Oct 20/91 Figure 6 32-41-0
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H80004
Hydraulic Brake System Schematic 591
32-41-0 Figure 7 Aug 15/80
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
HYDRAULIC BRAKE SYSTEM - TROUBLE SHOOTING
1. General
A. The following precheck items should be performed before trouble shooting the hydraulic brake system:
(1)
Perform brake system operation test (Ref Hydraulic Brake System - Adjustment/Test). If system malfunctions, see Hydraulic Brake System Trouble Shooting Chart.
(2)
Provide System A and B hydraulic power (Ref 29-11-0, Hydraulic System A - Maintenance Practices and 29-12-0, Hydraulic System B - Maintenance Practices).
(3)
Check that antiskid system is functioning normally (Ref 32-42-0).
(4)
Check that automatic braking system is functioning normally (Ref 32-43-01).
591
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500
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Feb 15/68 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 32-41-0 Page 103
HYDRAULIC BRAKE SYSTEM - MAINTENANCE PRACTICES
1. Bleed the Hydraulic Brake System
A. General
(1)
The brake hydraulic system must be bled when a hydraulic line of the brake system is opened or if a component connected to the system is replaced. When the system is bled, the air in the brake lines or a component of the brake system is transmitted to the reservoir by the return lines or released to the atmosphere.
(2)
The quantity of time to bleed the system will be kept to a minimum if the brakes are filled and bled on the bench.
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