32-41-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400 MAINTENANCE MANUAL
UPPER DECK FLOOR
NO. 1 ENTRY DOOR
SEE A
FIRST OFFICER'S BRAKE/RUDDER PEDALS
BRAKE
CABLES

CAPTAIN'S
RIGHT-BRAKE-CABLE-BRAKE/RUDDERCONTROL QUADRANT PUSH PEDALS
RODS
BELL
CRANK
PUSH ROD
BRAKE-PEDAL-BUS-CRANK ASSEMBLY PUSH RODSSTOP BUS RODSBELL CRANK
STOP BRAKE BRAKE-PEDAL-
CABLES BUS-CRANK ASSEMBLY
PUSH ROD
LEFT-BRAKE-CABLE-CONTROL QUADRANT
Brake Pedal Bus Component Location Figure 1
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 32-41-00
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
747-400
MAINTENANCE MANUAL

SEE  B 
SEE  A  KEEL BEAM 
MOUNTING BRACKET 
PRESSURE SWITCH HYDRAULIC-SYSTEM-2- NO. 1 ALTERNATE SOURCE SELECTOR VALVE 
MOUNTING BRACKET 
A  ACCUMULATOR ISOLATION VALVE 

ALTERNATE-SOURCE- LEFT-WING-GEAR 
SELECTOR VALVE  REAR SPAR 
NO. 2 
B 
Alternate-Source-Selector Valve and Accumulator 
Isolation Valve Component Location 
Figure 2 

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747-400
MAINTENANCE MANUAL

 E.  Alternate-source-selector valve 2 is connected to hydraulic systems as follows:
 -C1 is connected to hydraulic system 4
 -
C2 is connected by a T to BP of alternate-source-selector valve 1 - C3 is connected to the return line of hydraulic system number 2 so that pressure at this port will always be low

 F.  
With all hydraulic systems pressurized the selector valves operate as follows:

 -
Hydraulic pressure from hydraulic system 4 at alternate-source-selector valve 1 port C2 holds this valve closed

 -
Hydraulic pressure from hydraulic system 4 at alternate-source-selector valve 2 port C1 holds this valve closed

 -
Hydraulic system 4 supplies pressure to the normal-brake-metering valves to operate the brakes

 G.  
With pressure removed from hydraulic system 4 and full pressure on hydraulic system 1 and hydraulic system 2 the Valves operate as follows:

 -When pressure from hydraulic system 4 is removed from alternate-source-selector valve 1 port C2, the valve opens and supplies alternate brake metering valves from hydraulic system 1
 -
Pressure from hydraulic system 4 is also removed from alternate-source-selector valve 2 port C1, but this valve will not open because pressure from alternate-source-selector valve 1 BP is put on alternate-source-selector valve 2 port C2 to keep this valve closed.

 H.  
With pressure removed from hydraulic system 4 and hydraulic system 1 the valves operate as follows:

 -No pressure is applied at any of the control ports or the pressure port of Alternate-Source-Selector Valve 1, and the return spring in this valve will push it closed.
 -
Pressure at Alternate-Source-Selector Valve 2 port C2 is thus removed. This permits pressure at port P from hydraulic system 2 to hold the valve open and supply pressure to the alternate-brake-metering valves.

 I.  
During landing gear retraction the valves operate as follows:

 -
Pressure supplied from the landing gear retraction system (right body gear door operated sequence valve, port UPc) to alternate-source-selector valve 1 port C3 opens the valve and pressurizes the alternate brake metering valves during gear retraction.

 -
Alternate-Source-Selector Valve 2 stays closed as in normal hydraulic system operation.

 J.  
You can use proceedures in this section to remove and install the valves. A test on the valve is done after installation and also in the Hydraulic Brake System - Adjustment/Test (AMM 32-41-00/501).

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