BRAKE HYDRO-MECHANICAL CONTROL -BRAKE PEDAL BUS MECHANISM
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BRAKE HYDRO-MECHANICAL CONTROL -BRAKE METERING VALVE ASSEMBLY -GENERAL DESCRIPTION
Purpose
The brake metering valve assemblies get brake pedal input and control brake pressure.
Components
Each brake metering valve assembly includes these components:
*
Brake metering valve actuation/support assembly
*
Normal brake metering valve
*
Alternate brake metering valve.
Location
Normal and alternate brake metering valves attach to each other to make the brake metering valve assembly. There is a brake metering valve in each main landing gear wheel well. Each attaches to a brake metering valve actuation/support assembly.
These brake metering valve assemblies attach to the wing rear spar side of body fitting in the forward section of each wheel well.
Training Information Point
You can replace the brake metering valve as a unit with no change in brake cable rigging. To do this, remove the brake metering valve from the actuation/support assembly. After installation of the new valve, you can make small adjustments with the pushrod in the actuation/support assembly.
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BRAKE HYDRO-MECHANICAL CONTROL -BRAKE METERING VALVE ASSEMBLY -GENERAL DESCRIPTION
EFFECTIVITY BEJ ALL 32-41-00
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D633W101-BEJ Jan 05/2002
BRAKE HYDRO-MECHANICAL CONTROL -BRAKE METERING VALVE ASSEMBLY -FUNCTIONAL DESCRIPTION
General
On the brake metering valve assembly, the normal and alternate brake metering valves are almost the same. They bolt together and use the same input shaft.
Only one valve at a time gets pressure except during gear retract braking. The alternate source selector valve and the accumulator isolation valve control which metering valve gets pressure.
The normal brake metering valve uses right hydraulic system and accumulator pressure for the normal brake system.
The alternate brake metering valve uses center/reserve hydraulic system pressure for the alternate brake system when the right hydraulic system has low pressure. It also uses pressure from the landing gear retract line to stop the main gear wheel rotation during retraction.
Normal and Alternate Brake Application
The brake pedal command goes to the metering valves through cables and linkage. This moves the metering valve input shaft.
When the input shaft turns, it moves the metering valve spools in both valves at the same time.
The metering valve spools are spring-loaded to the brakes OFF position.
Metering valve spool movement sends pressure to the brakes and to the feedback chamber. This pressure applies the brakes and causes the feedback chamber to move the metering spool back to the brake pressure maintained position.
Brake pedal release permits the springs to return the metering spools in both valves to the brakes OFF position. This sends brake pressure to return and releases the brakes.
Gear Retract Wheel Braking
During landing gear retraction, landing gear retract pressure pressurizes the gear retract braking actuator.
The gear retract braking actuator moves a forked actuator lever to operate the alternate brake metering valve spool. This operation does not move the input shaft and does not back-drive the brake pedals.
The movement of the alternate metering valve spool sends approximately 550 psi of pressure to the brakes.
EFFECTIVITY BEJ ALL 32-41-00
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BRAKE HYDRO-MECHANICAL CONTROL -BRAKE METERING VALVE ASSEMBLY -FUNCTIONAL DESCRIPTION
EFFECTIVITY BEJ ALL 32-41-00
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Page 16 D633W101-BEJ Jan 05/2002
BRAKE HYDRO-MECHANICAL CONTROL -BRAKE ACCUMULATOR AND SERVICING COMPONENTS
General
The brake accumulator supplies brake pressure to the normal brake hydraulic system when the center and right hydraulic systems are off. It supplies enough pressure for six full brake applications or to keep the parking brake pressurized for eight hours.
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