B.  
Mounting Flange

 (1)  
The mounting flange is found on the coupling shaft end of the pump. The flange attaches the pump to the engine accessory drive pad.

 C.  
Housing

 (1)
The housing contains the following pumping mechanism components:

 -cylinder block
 -nine piston and shoe subassemblies
 -yoke
 -driveshaft.
 (2)  
The pumping action is generated by the piston and shoe subasemblies within the cylinder block and is dependent upon the displacement angle of the yoke.

 D.  
Valve Block and Inserts Subassembly

 (1)  
The valve block and inserts subassembly includes the solenoid-operated-depressurizing valve and the outlet blocking valve.

 (2)  
The inlet, outlet, and case drain ports are an important part of the valve block and inserts subassembly. The inlet and outlet ports give the connection between the hydraulic system and the pump. The case drain port gives the connection between the hydraulic system reservoir and the pump.

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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

SEE A
HYDRAULIC 
SUPPLY 
HOSE 
HYDRAULIC 
CASE DRAIN 
HOSE 
HYDRAULIC 
PRESSURE 
HOSE 

ENGINE-DRIVEN PUMPFWD
SEE B
A
Engine-Driven Pump Description and Operation Figure 1 (Sheet 1)
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

CASE RELIEF VALVE
VALVE BLOCK AND INSERTS SUBASSEMBLY
CASE FILL
AND BLEED
VALVE
PISTON AND SHOE SUBASSEMBLY
CYLINDER
BLOCK
HOUSING
ADAPTER BLOCK ASSEMBLY
PRESSURE COMPENSATOR VALVE
B
YOKE
Engine-Driven Pump Description and Operation
Figure 1 (Sheet 2)

MOUNTING FLANGE
DRIVE SHAFT
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 ALL  ú ú 02 Page 3 ú Dec 10/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

 E.  Adapter Block Subassembly
 (1)  The adapter block subassembly contains the following:
 -case fill and bleed valve
 -pressure compensator valve
 -case relief valve.
 (2)  
The case fill and bleed valve keeps the trapped air pockets in the pump case to a minimum. Trapped air pockets in the pump case could cause dry starts.

 (3)  
The pressure compensator valve has a spring-loaded pilot valve which operates within a bushing screw and adjusting screw which controls the preload on the spring-loaded pilot valve. The preload adjustment gives the system pressure at which the pump begins to decrease its yoke angle displacement.

 (4)  
The case relief valve lets the case fluid pass directly into the pump inlet when a case pressure surge occurs. This will prevent the housing from possibly breaking.

 3.  Operation
_________
 A.  To help make explanation of the operation easier, consider the pump in three circuits:
 -Main curcuit
 -Control circuit
 -
Lubrication circuit. The main circuit has the main flowpath to the inlet port, through the cylinder block, piston and shoe assemblies, and out of the outlet port to the system. The control circuit has the flow of fluid through the drilled sensing passages in the housing, adapter block, valve block, solenoid-operated depressurizing valve, blocking valve, and pressure compensator valve. The lubrication circuit has the flow of fluid in the housing.
　
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