*
The second stage keeps pressure to the brakes equal to the first stage controlled pressure.
The first stage uses a current controlled flapper between two nozzles to adjust first stage pressure. One nozzle connects to system pressure and the other connects to return.
When no current goes to the valve, the flapper moves against the return nozzle. In this position, control pressure is the same as system pressure.
When full current goes to the valve, the flapper moves against the pressure nozzle. In this position, control pressure is the same as return pressure.
For each intermediate value of input current, the flapper moves between the two nozzles to adjust the control pressure (shown).
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID MODULES -FUNCTIONAL DESCRIPTION
The second stage uses a spool valve that moves with first stage control pressure and a spring on one end and metered brake pressure on the other end.
When there is no metered brake pressure, the spring holds the spool in position to send initial brake metered pressure to fill the brakes before the shutoff valve opens.
When control pressure is more than metered brake pressure, the spool moves to send metered brake pressure to the brakes.
During antiskid operation, the spool operates to control brake pressure equal to first stage control pressure. It sends excess brake pressure to system return. A flow restrictor slows spool movement.
Hydraulic Fuse
Brake line fuses prevent fluid loss caused by external leakage downstream of the antiskid modules.
If 60 to 95 cubic inches of fluid pass through the fuse, it closes. When the pressure differential across the fuse is between 18 to 30 psi, the fuse automatically resets.
A bypass lever permits manual reset of the fuse. To reset manually, move the lever down to operate a bypass valve that equalizes pressure on each side of the fuse.
There is no indication that a fuse is set.
Return Check Valve
If the return line is blocked and metered pressure is less than return pressure, the return check valve releases brake pressure to metered pressure.
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ANTISKID/AUTOBRAKE SYSTEM -ANTISKID MODULES -FUNCTIONAL DESCRIPTION
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D633W101-BEJ Jan 05/2002
ANTISKID/AUTOBRAKE SYSTEM -ANTISKID SHUTTLE VALVE MODULE
Purpose
Two shuttle valve modules automatically select the highest metered pressure source and send it to the brakes.
Components
The shuttle valve modules are the same for the left and the right. Each module is an LRU and contains these LRUs:
*
Cartridge valves (6)
*
Filters (6)
*
A flight dispatch disconnect.
Location
The modules are forward of the left and right main landing gear beams. They are outboard of the main landing gear below the normal antiskid modules.
You get access to the modules through an access panel outboard of each main landing gear.
Functional Description
Each shuttle valve moves to a detented position to connect the input line with the higher metered pressure to the related brake line. The line with the lower pressure is blocked.
Fluid to each brake is put through a filter before it goes out of the module.
You use the shuttle valve to deactivate a brake in the normal brake system. To lock the related shuttle valve in the ALTERNATE position, you remove the end cover and install the flight dispatch disconnect. This permits gear retract pressure to the related brake with the normal brake deactivated.
Training Information Point
The system can operate with one brake on each six wheel truck deactivated.
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D633W101-BEJ Sep 05/2002
ANTISKID/AUTOBRAKE SYSTEM -ANTISKID SHUTTLE VALVE MODULE
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Page 25
D633W101-BEJ Jan 05/2002
ANTISKID/AUTOBRAKE SYSTEM -AUTOBRAKE VALVE MODULE
Purpose
The autobrake valve module gets BSCU electrical signals to send right hydraulic system pressure to the normal brake system during autobrake operation.
Components
The autobrake valve module is an LRU and contains these LRUs:
*
Solenoid valve
*
Solenoid valve pressure switch
*
Control valve
*
Control valve pressure transducer.
There is also a shutoff valve inside the module.
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