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 10. Case Drain Module
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 A.  The case drain module is installed aft of the reservoir in the strut. The case drain fluid which is used to lubricate the pump and keep the pump cool goes through the case drain filters. There is a separate filter element for the EDP and the demand pump. The case drain module has two filter elements with separate differential pressure indicators, three check valves, and a temperature sensor.
 11. Reservoir Pressurization Module
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 A.  The reservoir pressurization module is installed aft of the case drain module in the strut. The pressurization module supplies clean air pressure to the reservoirs. It also prevents hydraulic fluid reverse flow into the pneumatic duct. The module has two check valves, two filters, and a pressure relief valve.
 B.  The check valves in the pneumatic pressure lines prevent hydraulic fluid reverse flow into the air conditioning system.
 C.  The pressurization module receives air pressure from the pneumatic duct at 45 psi. The pressure relief valve will permit you to manually release the pressure in the reservoir.
 12. Hydraulic Interface Module (HYDIM)
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 A.  The HYDIM electrical cards are installed in the main equipment center on the left side of the nose gear wheel well. There is one HYDIM card for each system. The four cards are the same.
 B.  The HYDIM card controls and monitors the status of the hydraulic system. Each HYDIM card is supplied with 28 volt dc power from two different dc buses. One of the dc buses supplies power for the demand pump AUTO control and the other dc bus supplies power for hydraulic system indication.
 13. Operation
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 A.  Functional Description
 (1)  
The operation of each of the four main hydraulic fluid supply systems is the same. The only difference is that systems No. 1 and No. 4 have an auxiliary system for ground operatons.

 (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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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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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:

 -
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

 -
The trailing edge flaps are in operation

 -
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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