Remove and install the elevator PCU as one assembly with the reaction link. The elevator PCU disconnects from the kick link which stays on the airplane.
Use the cradle hoist ground service equipment (GSE) to support the PCU during removal and installation.
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ELEVATOR CONTROL -ELEVATOR PCU -INTRODUCTION

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ELEVATOR CONTROL -ELEVATOR PCU -PHYSICAL DESCRIPTION

Physical Description

All four elevator PCUs are identical. Each elevator PCU, with its reaction link, weighs about 85 lb (41 kg).
The outboard PCUs are powered by the left hydraulic system. The left inboard is powered by the center system and the right inboard is powered by the right system.
Each elevator PCU contains a hydraulic actuator with a control module. The control module contains:
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Electrohydraulic servo valve (EHSV)

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Pressure reducer solenoid valve which controls the pressure reducer valve

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Bypass solenoid valve

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Pressure sag check valve

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Blocking solenoid valve with two solenoid coils

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Mode selector valve with manual bypass

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Differential pressure sensor

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Bypass check valves with restrictors (2)

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Thermal relief valve

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Compensator/relief valve with quantity indicator

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Manual test valve for the compensator/relief valve

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Anti-cavitation check valves with restrictors (2)

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Inlet check valve

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Inlet filter.

Hydraulic Actuator
The actuator piston has an LVDT that sends actuator position feedback signals to the ACE. The actuator piston also has a null LVDT to adjust the null position of the actuator piston LVDT during installation of the PCU.
EHSV
The EHSV controls the hydraulic power to the extend and retract sides of the actuator. The EHSV has an LVDT that sends EHSV position feedback signals to the ACE.
Pressure Reducer Solenoid Valve
The ACE that commands the adjacent PCU controls the pressure reducer solenoid valve. The pressure reducer solenoid valve commands the pressure reducer valve to decrease the hydraulic pressure to 2140 psi. Reduced pressure on the actuator decreases the probability of a leak and decreases fatigue loads during normal operation.
In case of failure of a PCU or its hydraulic source, the hydraulic pressure to the other PCU increases to the nominal hydraulic system pressure of 3000 psi. This permits the other PCU to increase its capacity.

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ELEVATOR CONTROL -ELEVATOR PCU -PHYSICAL DESCRIPTION

Bypass Solenoid Valve

The on-side ACE commands the bypass solenoid valve. The bypass solenoid valve controls the pilot pressure from the hydraulic system to the mode selector valve.
Pressure Sag Check Valve

The pressure sag check valve prevents pressure decreases from affecting the position of the mode selector valve.
Blocking Solenoid Valve

The on-side ACE controls one coil of the blocking solenoid valve, the ACE commanding the adjacent PCU controls the other coil. The blocking solenoid valve controls the pilot pressure from the actuator to the mode selector valve.
Mode Selector Valve

Pilot pressure from the bypass or the blocking solenoid valves commands the mode selector valve to one of these positions:
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Normal

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Bypass

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Blocking.

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.
EFFECTIVITY
BEJ ALL

Bypass Check Valves with Restrictors
The two bypass check valves permit pressure from either side of the actuator to reach the blocking solenoid valve. The restrictors prevent pressure fluctuations from affecting the position of the mode selector valve.
Thermal Relief Valve
The thermal relief valve protects the actuator from thermal expansion of the hydraulic fluid.
Compensator/Relief Valve with Quantity Indicator
The compensator/relief valve holds a small quantity of fluid at a pressure slightly above the hydraulic system return pressure. This fluid is available to the actuator to prevent cavitation.
The indicator shows the quantity of fluid in the compensator.
Manual Test Valve
You use the manual test valve to test the proper operation of the compensator/relief valve. With the manual test valve open, the compensator/relief valve pressure decreases. Check that the quantity indicator moves to the empty position.
　
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