EFFECTIVITY BEJ ALL 27-21-00
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RUDDER CONTROL -RUDDER PCU -PHYSICAL DESCRIPTION
Mode Selector Valve
Pilot pressure from the bypass or the damped solenoid valves commands the mode selector valve in one of three positions:
*
Normal
*
Bypass
*
Damped.
Differential Pressure Sensor
A differential pressure sensor measures the pressure difference between both sides of the actuator piston. The sensor operates an LVDT which sends signals to the ACE.
Bypass Check Valves
The two bypass check valves permit pressure from either side of the actuator to reach the damped solenoid valve.
Relief Valves
The two relief valves protect the actuator in case of high pressure due to a hardover of an adjacent PCU.
Thermal Relief Valve
The thermal relief valve protects the actuator from thermal expansion of the hydraulic fluid.
Compensator/Relief Valve
The compensator/relief valve holds a small quantity of fluid above the hydraulic system return pressure. This fluid is available to the actuator to prevent cavitation.
Anti-cavitation Check Valves
The two anti-cavitation check valves permit return fluid from the compensator to flow to the actuator. This prevents cavitation of the actuator during rapid backdriving of the PCU.
Inlet Check Valve
The inlet check valve keeps the hydraulic fluid in the actuator when the hydraulic system power is lost.
Inlet Filter
The inlet filter protects the actuator from solids in the hydraulic fluid.
Training Information Point
Only the bearings in the actuator rod end and the reaction link, where they attach to the rudder, require lubrication.
All other bearings on the actuator and reaction link are teflon coated bearings. They do not require lubrication.
EFFECTIVITY BEJ ALL 27-21-00
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RUDDER CONTROL -RUDDER PCU -PHYSICAL DESCRIPTION
EFFECTIVITY BEJ ALL 27-21-00
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D633W101-BEJ Jan 05/2002
777 AIRCRAFT MAINTENANCE MANUAL
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27-21-00
Page 48 D633W101-BEJ Jan 05/2002
RUDDER CONTROL -RUDDER PCU -FUNCTIONAL DESCRIPTION
General
The rudder PCU operates in three different modes:
*
Normal
*
Bypass
*
Damped.
In the normal mode, the ACE energizes the bypass solenoid. The pressure reducer and the damped solenoid may or may not be energized.
In the bypass mode, the ACE de-energizes the bypass solenoid. The damped solenoid stays energized. The pressure reducer solenoid may or may not be energized.
In the damped mode, the ACE de-energizes the bypass solenoid and the pressure reducer solenoid. The damped solenoid is also de-energized.
PCU Operational Matrix
The table shows the various conditions of the PCU valve solenoids in the three modes of operation of the PCUs:
SOLENOID CONDITIONS PCU MODES OF OPERATION
NORMAL BYPASS DAMPED
PRESSURE REDUCER SOLENOID E/D *[1] *[2] E/D *[1] *[2] D *[2]
EFFECTIVITY BEJ ALL
SOLENOID CONDITIONS PCU MODES OF OPERATION
NORMAL BYPASS DAMPED
BYPASS SOLENOID E *[1] D *[2] D *[2]
DAMPED SOLENOID E/D *[1] *[2] E *[1] D *[2]
*[1] E = ENERGIZED *[2] D = DE-ENERGIZED
Normal mode
The PCU is in normal mode when the ACE energizes the bypass solenoid. Hydraulic pilot pressure then moves the mode selector valve to the normal position.
For the conditions of the other PCUs, the ACE may or may not energize the pressure reducer solenoid and the damped solenoid. The status of the damped solenoid does not affect the operation in the normal mode.
When the pressure reducer solenoid is energized, the pressure reducer valve regulates the pressure to the EHSV to a lower nominal value. When the pressure reducer solenoid is de-energized, the pressure reducer valve allows full hydraulic system pressure to the EHSV.
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