(2)
The reservoir supplies a positive flow of hydraulic fluid to the EDP, demand pump, and the auxiliary pump in system No. 4. Fluid from the reservoir will go through the normally open supply (fire) shutoff valve to the EDP. Fluid goes directly from the reservoir to the demand pumps and the auxiliary pump. The pressure output of the pumps is put through filters in the pressure module. The pressure module then sends the pressure output to the hydraulically powered airplane systems. The check valves in the pressure module control the fluid flow.
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747-400
MAINTENANCE MANUAL
(3)
The hydraulic fluid is then sent back through the return filter module and into the reservoir. If the filter is clogged the fluid is bypassed in the return module.
(4)
The hydraulic pumps are cooled and lubricated with hydraulic fluid flow through the case. The case drain fluid is then put through the case drain module, the heat exchanger, the return module, and back to the reservoir.
(5)
The operation of the EDP is controlled by the position of the ENGINE PUMPS switch on the hydraulic control panel. The normal position of the switch with the engine in operation is ON. If the switch is put in the OFF position, the output of the EDP will be blocked. When the pump is off, the only output will be the case drain flow which is necessary to cool and lubricate it. If you pull the engine fire handle the hydraulic supply shutoff valve will operate and stop the flow of fluid to the pump.
(6)
The operation of the ADP and the ACMP is controlled by the position of the DEMAND PUMPS switch on the hydraulic control panel. The pumps will operate continuously when the switch is put in the ON position. The pumps will not operate and stop if they are in operation when the switch is put in the OFF position.
(a)
When the switch for systems No. 1 and No. 4 is put in the AUTO position, the ADP will operate during the conditions that follow:
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The pressure of the EDP output decreases below 1,400 psi for more than 0.3 second. The ADP will operate for 14 seconds after the EDP output increases above 1,600 psi
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The trailing edge flaps are in operation
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The trailing edge flaps are put in a non-zero position and the airplane is in the air. The ADP will operate for 10 seconds after the flaps are put in the zero position.
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