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ELEVATOR CONTROL -ELEVATOR PCU -PHYSICAL DESCRIPTION
Anti-Cavitation Check Valves with Restrictors
The two anti-cavitation check valves permit return fluid from the compensator/relief valve to flow to the actuator. This prevents cavitation of the actuator during rapid backdriving of the PCU. The restrictors maintain elevator panel stiffness in case a check valve fails open.
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
A manual bypass valve permits movement of the PCU manually. Hydraulic power must be off before you use the manual bypass valve.
To move the elevator for maintenance, access the manual bypass valve. Turn the valve on both PCUs with the special tool while moving the elevator. After release of the manual bypass, it closes.
After installation of the elevator PCU, the actuator null LVDT requires adjustment. Remove the null LVDT access cover to adjust the actuator null LVDT.
During periodic inspection, you use the manual test valve to check the proper function of the compensator/relief valve. Remove hydraulic power from the PCU then move the manual test valve to release pressure internal to the compensator/relief valve. Do a check to see that the compensator/relief valve indicator moves all the way to its empty position.
The bearings in the actuator rod end and the reaction link require lubrication.
All other bearings on the actuator and the reaction link are teflon coated. They do not require lubrication.
EFFECTIVITY BEJ ALL 27-30-00
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ELEVATOR CONTROL -ELEVATOR PCU -PHYSICAL DESCRIPTION
EFFECTIVITY BEJ ALL 27-30-00
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777 AIRCRAFT MAINTENANCE MANUAL
THIS PAGE IS INTENTIONALLY LEFT BLANK
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ELEVATOR CONTROL -ELEVATOR PCU -FUNCTIONAL DESCRIPTION
General
The elevator PCU operates in three different modes:
*
Normal
*
Bypass
*
Blocking.
In the normal mode, the ACE energizes the bypass solenoid and at least one of the coils of the blocking solenoid. The ACE energizes or de-energizes the pressure reducer solenoid.
In the bypass mode, the ACE de-energizes the bypass solenoid and energizes at least one of the coils of the blocking solenoid. The ACE energizes the pressure reducer solenoid.
In the blocking mode, the ACE de-energizes:
*
The bypass solenoid
*
Both coils of the blocking solenoid
*
The pressure reducer solenoid.
The solenoid of the blocking valve has two coils. When both coils are de-energized, the valve is in its relaxed state. When one or both coils of the solenoid is energized, the valve moves.
PCU Operational Matrix
The table below shows the various conditions of the PCU valve solenoids in the three modes of operation.
EFFECTIVITY
BEJ ALL
SOLENOID CONDITIONS PCU MODES OF OPERATION
NORMAL BYPASS BLOCKING
BYPASS SOLENOID E *[1] D *[2] D *[2]
BLOCKING SOLENOID COIL 1 E *[1] E/D *[1] *[2] D *[2]
BLOCKING SOLENOID COIL 2 E/D *[1] *[2] E *[1] D *[2]
PRESSURE REDUCER SOLENOID E/D *[1] *[2] E *[1] D *[2]
*[1] E = ENERGIZED *[2] D = DE-ENERGIZED
Normal mode
The PCU is in the normal mode when the ACE energizes the bypass solenoid and at least one coil of the blocking solenoid. In the normal mode, the ACE energizes the pressure reducer solenoid when there is no failure of the ACE or the PCU.
With the bypass and blocking solenoids energized, hydraulic pressure moves the mode selector valve to the normal mode position. An electrical command to the EHSV results in the actuator extension or retraction.
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ELEVATOR CONTROL -ELEVATOR PCU -FUNCTIONAL DESCRIPTION
When the ACE energizes the pressure reducer solenoid, the pressure reducer valve reduces the hydraulic pressure to 2140 psi. When there is a failure of the adjacent PCU, the ACE de-energizes the pressure reducer solenoid. The actuator then operates with full hydraulic system pressure (3000 psi).
Bypass Mode
The PCU is in the bypass mode when the ACE de-energizes the bypass solenoid and energizes one coil of the blocking solenoid.
This happens when there is a failure on the PCU or the ACE in control of the PCU.
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