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R  Door Actuator Schematic Figure 006
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 The extension mode makes sure that the high-pressure (HP) fluid can flow through the valve to extend the door actuators. In the neutral mode, the HP fluid can not flow through the valve. For safety reasons, the interim mode pressurizes first the extension sides (port A) of the door actuators. This prevents a sudden movement of the cargo door to a lower position when it starts to close. When the pressure is sufficient, the valve can move in the retraction mode. The HP fluid can then flow through the valve to pressurize the door actuators on the retraction sides (port B).
 The electrical selector valve 2500MJ is installed on the Yellow ground service panel of the aft, right belly fairing. The valve housing includes:
 -
a solenoid-operated control valve,

 -
a hydraulically operated main valve,

 -
a leakage restrictor. The electrical selector valve 2500MJ controls the normal and the manual mode of the door hydraulic system. When the solenoid is energized, it moves the control valve in position which lets the HP fluid operate the main valve. The pressure puts the main valve in position and the HP fluid can flow to pressurize the door hydraulic system (normal and/or manual mode). The leakage restrictor allows residual system pressure to drain into the return line. The door actuators 2502MJ and 2503MJ (2505MJ and 2506MJ) are installed at FR26A (FR54A) and FR25A (FR53A) . They are attached between the actuator attachment fitting on the door structure and the actuator beam of the fuselage structure.

 Usually, the door actuators 2502MJ and 2503MJ (2505MJ and 2506MJ) extend in parallel and divide the total load of the cargo door. If one door actuator fails, the other is sufficient to operate the cargo door with the same performance.
 Extension of the Door Actuator:
R  (Ref. Fig. 006) When HP fluid flows through the port A of the door actuator, the piston of the door actuator extends. When the piston is fully extended, the pawls on the piston end move around an internal lock. The pawls then press the locking piston against the spring of the locking cylinder.
 When the hydraulic pressure to the port A is shut off, the spring pressure operates the locking piston. The locking piston moves a small distance against the pawls and presses them against the internal lock. Thus, the door actuator is mechanically locked in its extended position.
 While the door actuator is locked, the pawls operate the target of the proximity switch with a lever. The proximity switch sends a signal to the indicator light 9MJ (8MJ) on the control panel.
 1EFF : ALL 1 52-36-00Page 14 1 1 Aug 01/05 1 1 1CES 1 Retraction of the Door Actuator: When the HP fluid flows through the port B of the door actuator, the piston of the door actuator retracts. When the door actuator is in the extended locked position, the HP fluid operates the locking piston against the spring. The pawls come free from the internal lock and release the mechanical lock. At the same time, the target of the proximity switch moves back. The door actuator is no longer mechanically locked and the piston of the door actuator retracts.

 The hand pump 3009GM is installed on the Yellow ground service panel of the right, aft belly fairing. The operation of the handpump pressurizes the door hydraulic system. A pressure relief valve, installed on the pressure outlet of the handpump, prevents too high pressure during the manual operation.
 The double check valve 3717GM, which includes a normal and a bypass check valve, is installed in the supply line of the door hydraulic system. The normal check valve opens the supply line when the system pressure increases to 5.5 bar. It prevents also a loss of hydraulic fluid during flight if a leakage in the supply line occurs. The bypass check valve makes sure that the supply line is depressurized after each hydraulic operation of the cargo door.
 The check valve 3188GM is installed in the return line of the door hydraulic system. It protects the door hydraulic system against a pressurization of the low-pressure system.
 5. Operation_________
 NOTE : The identification numbers in brackets are for the components of the
____
 AFT cargo compartment door.

 A. Normal Opening Procedure
 To operate the door hydraulic system, make sure that the FWD (AFT) cargo
 door is in the "Unlocked" condition. The cargo door is unlocked when:
 -
the door locking handle is out of its recess and

 -
the door locking handle is in the "Unlocked" position.

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