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RAM AIR TURBINE SYSTEM -RAT CHECKOUT MODULE -INTRODUCTION
RAT Module Solenoid Valve
The RAT module solenoid valve controls hydraulic system pressure to the stow valve during retraction of the RAT actuator. The valve permits the RAT to fully retract only when the turbine blades are locked.
RAT Stow Valve
The RAT stow valve is a manually operated valve which has three positions:
*
STOW
*
STOP
*
FLIGHT.
A manual lever controls the valve position. The RAT stow valve controls center hydraulic system pressure to the RAT actuator during RAT retraction.
To operate the RAT stow valve, it is first necessary to remove the lever lockwire. You pull on the lever T-handle and move the lever up to unlock the lever from the FLIGHT position. You can then move the lever fully up, with the T-handle released, to the STOW position to retract the RAT.
To stop the RAT retraction, you move the lever down, with the T-handle released, until the lever lock touches the stop. In the STOP position the RAT stow valve stops the hydraulic flow to retract the actuator.
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When the RAT retraction is complete, you move the lever fully down, with the T-handle pulled, to the FLIGHT position and release the T-handle to lock the lever. You then install a lockwire on the lever. In the FLIGHT position, the valve connects both sides of the RAT actuator to the center hydraulic system return to permit extension.
The RAT stow valve has a switch that monitors the position of the valve.
RAT Motoring Valve
The RAT motoring valve is a manually operated valve which has two-positions:
*
FLIGHT
*
MOTOR.
The valve permits center hydraulic system pressure to backdrive the RAT during ground operational tests.
To operate the RAT motoring valve it is first necessary to remove the lever lockwire. You then turn the lever handle 90 degrees counterclockwise so when you move the lever up, the lever tab slides between the fork on the RAT checkout module. When the lever is fully up, the valve is in the MOTOR position and permits hydraulic flow to the RAT pump.
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RAM AIR TURBINE SYSTEM -RAT CHECKOUT MODULE -INTRODUCTION
When the RAT motoring is complete, you move the lever fully down to the FLIGHT position and release the handle. The handle internal spring turns the handle. It is then necessary to install a lockwire on the lever.
Training Information Point
The RAT extension time is approximately two seconds. The RAT retraction time is approximately 45 seconds.
It is necessary to install a protection cage around the RAT when you do the backdrive operational test of the RAT.
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RAM AIR TURBINE SYSTEM -RAT CHECKOUT MODULE -INTRODUCTION
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777 AIRCRAFT MAINTENANCE MANUAL
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RAM AIR TURBINE SYSTEM -RAT CHECKOUT MODULE -PHYSICAL DESCRIPTION
General
The RAT checkout module has these components (some of which are LRUs):
*
RAT stow valve
*
RAT stow valve position switch
*
RAT module solenoid valve (LRU)
*
RAT motoring valve
*
Start-up quantity bypass fuse (LRU)
*
Pressure and case drain filters (LRU)
*
Check valve (5)
*
Pressure relief valve
*
Pressure transducer (LRU)
*
Thermal bleed orifice.
RAT Stow Valve
The RAT stow valve is manually operated and has three positions:
*
STOW
*
STOP
*
FLIGHT.
A lever controls the valve position. The valve is spring-loaded to the FLIGHT position.
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In the STOW position, the RAT stow valve permits center hydraulic system pressure to the RAT actuator for RAT retraction. In the STOP position, the valve stops hydraulic pressure to the RAT actuator. In the FLIGHT position, the valve connects both sides of the actuator to the center hydraulic system return to permit extension.
RAT Stow Valve Position Switch
The RAT stow valve position switch actuates when the RAT stow valve leaves the FLIGHT position. When the RAT stow valve is in the FLIGHT position, the switch sends a ground signal to the HYDIM card. When the RAT stow valve is not in the FLIGHT position, the switch closes to supply a ground to the solenoid of the RAT module solenoid valve.
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