(b)
In this way the valve mechanism transmits hydraulic pressure to the brake port in proportion to the amount of force put on the lever.
(c)
When the force on the lever is removed, the spool is pushed to the off position by the return spring. This opens the brake port to the return port and releases pressure from the brake lines.
(2)
The wheel despin actuator operates brakes during gear retraction to stop wheel spin before the wheel goes into the wheel well.
(a)
The wheel despin actuator has one port that is connected to the gear retraction hydraulic system. It contains a piston which is held by a spring to the off position.
(b)
When the gear retraction lines are pressurized, hydraulic fluid goes into the port and moves the piston. The piston moves the spool in the alternate-brake-metering valve. This supplies pressure to the brakes as long as there is hydraulic pressure on the gear retraction system.
(c)
When gear retraction pressure is removed the springs move both the piston in the actuator and the spool in the metering valve back to the off position. This releases pressure from the brakes.
E.
You can remove and install a brake-metering-valve assembly using procedures in this section. A brake system operational test makes sure it operates correctly.
(1)
All adjustments to the brake-metering-valve assembly are done during shop overhaul. The brake-metering-valve assembly is very sensative. Thus we do not recommend that you disassemble it while it is installed on the airplane.
10. Brake-Hydraulic-Disconnect Assembly (Fig. 6)
___________________________________
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32-41-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
SEE A
BLEEDER
VALVE
BRAKE-HYDRAULIC DISCONNECT-INNER COUPLING-HALF
ADJUSTER/PISTON
ASSEMBLY
(7 LOCATIONS)
HYDRAULIC LINE
BRAKE-HYDRAULIC
DISCONNECT-OUTER
COUPLING-HALF
NUT
WASHER
BRAKE
BRAKE TORQUE
EQUALIZER ARM BOLT ROD
A
Landing Gear Brake Unit Component Location Figure 6
STATOR DISK (3 LOCATIONS)
PISTON HOUSING
ROTOR DISC (4 LOCATIONS)
WEAR INDICATOR PIN (2 LOCATIONS)
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ALL ú ú 01 Page 14 ú Jun 10/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL
A. The hydraulic-brake-disconnect assembly connects the brake to the hydraulic pressure source. The hydraulic-brake-disconnect assembly contains two coupling halves. The inner half is installed into the brake boss, and the outer half is attached to the hydraulic line. Each coupling half seals automatically in the disconnected position. This prevents air from entering the brake or the hydraulic line when the brake is disconnected from the hydraulic system.
B. The outer coupling half contains two detent pins which lock the two coupling halves together.
C. To connect the brake to the hydraulic system you push the outer coupling half into the inner coupling half until the detent pins move out. To disconnect the brake you push in on the detent pins and pull the outer coupling half from the brake.
D. The hydraulic-brake-disconnect assembly can be removed and replaced if there is a malfunction or it is damaged. No other maintenance is done on the disconnect while it is installed on the airplane.
11. Brake Unit (Fig. 6)
__________
A. A hydraulically operated, multiple-disk brake is used on each wheel of the body gear and wing gear. The same brake is used on all body and wing gear positions, so the brakes are interchangeable. The brake uses only BMS 3-11 type hydraulic fluid and operates at pressures from 160 to 3000 psi. The brake is made so that it can be removed with the wheel assembly if the brake components become seized to the wheel during operation.
B. The brake contains these three primary components:
-
The piston housing and parts
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