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 (1)  The electric-motor-actuated-cartridge valve is a three-way, two position valve operated by an 18 - 30 vdc motor. When the actuator is in position 1, the pressure and return ports of the valve are blocked. When the actuator is in position 2, the pressure and return ports are connected together. When the valve is in transit, all ports are blocked.
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 32-44-00
 ALL  ú ú 10 Page 4 ú Feb 10/97
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
HYDRAULIC BRAKE
ACCUMULATOR
SEE A
INBOARD BULKHEAD
RIGHT BODY GEAR
WHEEL WELL

MOTOR OPERATED SHUTOFF VALVE
THERMO PRESSURE RELIEF VALVE
ELECTRICAL
CONNECTOR

THERMAL
RELIEF
PARKING

VALVE
CHECK  PARKING
BRAKE
VALVE CHECK BRAKE
MODULE VALVE MODULEFWD MOTOR OPERATED
A1
SHUTOFF VALVE
PARKING BRAKE MODULES WITH INTERNAL THERMAL RELIEF VALVE,
RELIEF VALVE NOT INSTALLED ON ALL AIRPLANES

1 A2
2 PARKING BRAKE MODULES WITH EXTERNAL THERMAL RELIEF VALVE
Parking Brake Module
Figure 3

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 32-44-00
 ALL  ú ú 01 Page 5 ú Jun 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 (2)  
The electric motor contains two fields and two limit switches. One field turns the motor in a counterclockwise direction to position 1, and the other field turns the motor in a clockwise direction to position 2. When the parking brake is set, power is applied to the position 1 field, and the motor cycles all the way to position 1. At position 1 a limit switch disconnects the position 1 field from parking brake set circuit and connects the position 2 field to the parking brake off circuit. When the parking brake is released the position 2 field is powered and the motor turns clockwise to position 2 where the limit switch disconnects the position 2 field from the parking brake off circuit and connects the position 1 field back to the parking brake on circuit.

 C.  
A Thermal-Pressure-Relief valve is installed adjacent to the Parking Brake Module and connects the IN-A port to the IN-B port. This protects the brake system from pressure buildup which is caused by expansion when a cold soaked airplane begins to warm. The valve opens and releases fluid into the return lines when pressure in the brake lines exceeds 3400 psi. When pressure drops below 3100 psi the valve closes.

 5.  Operation (Fig. 4)
_________
 A.  Functional Description
 (1)  
The parking brakes operate off the normal braking system. The pressure source is the hydraulic brake accumulator which is pressurized by hydraulic system 4.

 (2)  
When the control pedals are pushed into the stops and the parking brake lever is pulled, the linkage moves two pawls toward the brake pedal bellcrank. The pawls engage lockpins on the bell crank and hold the brake linkage in the applied position. The parking brake linkage will not set unless both brake pedals are pushed to the applied position.

 (3)  
When the parking brake lever is pulled and the linkage operates a switch that provides 28 vdc power to the electric motor in the parking brake modle. The motor cycles the module to the closed position. This blocks the normal antiskid valve return lines to prevent the accumulator from discharging through the antiskid valves.

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 32-44-00
 ALL  ú ú 06 Page 6 ú Apr 10/89
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

LH FORWARD WHEEL WELL
Parking Brake System Schematic Figure 4
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