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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 MAIN HYDRAULIC SUPPLY SYSTEM - MAINTENANCE PRACTICES
____________________________________________________
 1.  General_______
 A.  This procedure contains these tasks:
 (1)
Hydraulic system pressurization with a ground service cart.

 (2)
Hydraulic system pressurization with a demand pump.

 (3)
Hydraulic system pressurization with an engine-driven pump (EDP).

 (4)
Hydraulic system pressurization with an auxiliary AC hydraulic pump.

 (5)
Hydraulic system depressurization.

 (6)
Flush the hydraulic system.

 (7)
Bleed the hydraulic system.

 (8)
Flush an EDP pressure line and case drain line.

 (9)
Flush a demand pump pressure line and case drain line.

 (10)
 Flush a return line.

 (11)
 Hydraulic system fluid replacement.

 B.  
Flush the pressure and the case drain lines when a pump failure causes contamination that can cause check valve failure. Pump failure usually results in the release of large pieces of metal debris into the hydraulic system and causes the check valve failure.

 C.  
It can be necessary to flush the hydraulic system and replace or examine the filter elements if there is a hydraulic system failure. The table below contains the failure conditions and the procedures that are necessary to correct the failure.

 ~............................................................................... | CONDITION | CONDITION | PROCEDURE TO CORRECT THE CONDITION | | NO. | | | ................................................................................. | 1. | A pump failure that does| 1. It is not necessary to flush the | | | not cause a hydraulic | sytem. | | | fluid contamination | 2. Do a check of the pressure and | | | | case drain module differential | | | | pressure indicators. If any are | | | | extended, replace the filter | | | | elements (AMM 29-11-18/201 and | | | | 29-11-23/201). | | | | 3. It is not necessary to replace the | | | | return filter element. | ................................................................................. | 2. | A pump failure that | 1. Flush the pressure and the case | | | causes hydraulic fluid | drain line (Ref par. 7 or 8 as | | | contamination. | applicable). | | | | 2. Replace the two filter elements in | | | | the pressure module (AMM | | | | 29-11-23/201). Replace the case | | | | drain filter element for the | | | | applicable pump (AMM 29-11-18/201). | | | | 3. Do a check of the differential | | | | pressure indicator for the return | | | | module. If it has extended, refer | | | | to condition No. 4. | .................................................................................
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 29-11-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
 ~............................................................................... | CONDITION | CONDITION | PROCEDURE TO CORRECT THE CONDITION | | NO. | | | .................................................................................
 | 3. | A pump overheat because | 1.  Examine the supply, the pressure,  |
 |  | the supply fluid  |  and the case drain hoses and the  |
 |  | decreased.  |  heat shields for heat damage.  |
 |  |  |  Replace all the components that  |
 |  |  |  have heat damage.  |
 |  |  | 2.  Flush the pump pressure and the case|
 |  |  |  drain lines (Ref par. 7 or 8 as  |
 |  |  |  applicable).  |
 |  |  | 3.  Replace the pressure and the case  |
 |  |  |  drain filter elements  |
 |  |  |  (AMM 29-11-23/201 and 29-11-18/201).|

 ................................................................................. | 4. | The differential | 1. Replace the filter element for the | | | pressure indicator for | return module (AMM 29-11-29/201). | | | the return filter module| 2. Flush the return line (Ref par. 9). | | | extends because of a | 3. Flush the pressure and the case | | | pump failure that | drain lines (Ref par. 7 or 8, as | | | causes hydraulic fluid | applicable). | | | contamination. | 4. Replace the filter elements in the | | | | pressure module (AMM 29-11-23/201). | | | | Replace the case drain filter for | | | | the applicable pump (AMM | | | | 29-11-18/201). | ................................................................................. | 5. | A failure of the check | 1. Replace the check valve which does | | | valve for the pressure | not operate. Disassemble and clean | | | or the case drain line | the remaining check valves in the | | | occurs due to a pump | pressure and case drain lines and | | | failure | modules (AMM 29-11-06/401, | | | | 29-11-07/401, 29-11-08/201, and | | | | 29-11-23/201). | | | | 2. Flush the pressure and the case | | | | drain lines (Ref par. 7 or 8, as | | | | applicable. | | | | 4. Do a check of the differential | | | | pressure indicator on the return | | | | module. If it has extended, refer | | | | to condition No. 4. | .................................................................................
　
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