777 AMM 飞机维护手册 发动机排气 Engine Exhaust PW 777 AIRCRAFT MAINTENANCE MANUAL(34)

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The isolation valve solenoid valve is installed on the isolation valve body with four screws and washers. The screws are lockwired. If the isolation valve solenoid valve is replaced on the isolation valve, there is packing that is replaced on the electrical plug on the solenoid valve. In addition, a solenoid gasket which seals the base of the solenoid valve to the valve body is replaced.
Check Valve

The isolation valve uses an internal check valve in the hydraulic system return line to prevent a pressure surge that can unlock the TRAS. The check valve is ported to vent hydraulic pressure to hydraulic return port (SYS RTN).
Training Information Point
Use the bypass valve for ground maintenance when you manually extend and retract the T/R sleeve. When you open the bypass valve, the hydraulic fluid in the TRAS hydraulic tubing can return to the hydraulic system return line which prevents hydraulic lock. However, if TRAS hydraulic components must be removed, remove the pin from the crank to close the bypass valve to prevent drainage from the hydraulic system return lines.
The isolation valve is a line replaceable unit (LRU). These isolation valve components are also LRUs:
*
Directional control valve solenoid valve

*
Isolation valve solenoid valve

*
Hydraulic pressure switch.

 

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TRAS -ISOLATION VALVE

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TRAS -DIRECTIONAL CONTROL VALVE

Purpose

The directional control valve (DCV) supplies hydraulic pressure to extend or retract the T/R actuators.
Physical Description

The directional control valve (DCV) has these hydraulic connections:
*
TRAS return port (TRAS RTN)

*
TRAS pressure port (TRAS PRESS)

*
Control pressure port (CONTROL)

*
Retract pressure port (RETRACT)

*
Extend pressure port (EXTEND).

 

The dry weight of the directional control valve (DCV) is 6.45 pounds (2.92 kilograms).
The names of the ports (TRAS RTN, TRAS PRESS, CONTROL, RETRACT, EXTEND) are etched on the valve housing. Union fittings and packing are installed in all hydraulic ports.
The DCV is controlled with hydraulic pressure from the directional control valve solenoid valve on the isolation valve (IV). The DCV has an internal spring, main slide and auxiliary slide. A proximity sensor is mounted on the DCV to give the valve position indication.
　
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