(4)  
Advisory and status messages will be shown on the auxiliary EICAS display. HYD PRESS DEM 1,2,3, or 4 will be shown if the demand pump is put in the off position or the outlet pressure is less than 1,400 psi. HYD PRESS ENG 1,2,3, or 4 will be shown if the EDP outlet pressure is less than 1,400 psi.

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A

747-400
MAINTENANCE MANUAL

SEE A
PRESSURE MODULE
DEMAND PUMP
LOW PRESSURE
SWITCH

ENGINE-DRIVEN PUMP LOW FWD PRESSURE SWITCH
A
Hydraulic Low Pressure Warning Switch Location
Figure 1

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747-400
MAINTENANCE MANUAL

DEMAND PUMP LOW PRESSURE LIGHT
ENGINE-DRIVEN PUMP LOW PRESSURE LIGHT

HYDRAULIC CONTROL MODULE

Hydraulic Low Pressure Warning Indicators
Figure 2

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747-400
MAINTENANCE MANUAL

Hydraulic Low Pressure Warning System Simplified Schematic
Figure 3

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747-400 MAINTENANCE MANUAL
 HYDRAULIC LOW PRESSURE WARNING SWITCH - REMOVAL/INSTALLATION
____________________________________________________________
 1.  General_______
 A.  This procedure has two tasks. The first task removes the hydraulic low pressure warning switch (referred to as the switch). The second task installs the switch. The second task also does a test of the switch.
 B.  These procedures are applicable to the switch for the engine-driven pump (EDP) and the demand pump in all hydraulic systems.
 C.  You must open the doors in the trailing edge fairing to get access to the switch.
 TASK 29-34-01-004-001
 2.  Hydraulic Low Pressure Warning Switch Removal (Fig./401)_____________________________________________
 A.  References
 (1)  
AMM 29-11-00/201, Main Hydraulic Supply System

 (2)  
AMM 54-62-00/201, Nacelle Strut Access Panels

 B.  
Access

 (1)  
Location Zone
 454 System 1 - Strut Trailing Edge Fairing
 464 System 2 - Strut Trailing Edge Fairing
 474 System 3 - Strut Trailing Edge Fairing
 484 System 4 - Strut Trailing Edge Fairing

 (2)  
Access Panel
 454A Trailing Edge Fairing Doors - System 1
 464A Trailing Edge Fairing Doors - System 2
 474A Trailing Edge Fairing Doors - System 3
 484A Trailing Edge Fairing Doors - System 4

 C.  
Procedure

 S 014-002
 (1)  
Open the left and right doors in the trailing edge fairing (AMM 54-62-00/201).

 (2)
Release the pressure in the hydraulic system (AMM 29-11-00/201).

 S 864-003
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