747-400 AMM 飞机维护手册 气动系统 WATER/WASTE(25)

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Pressure Switch (Fig. 1 and 2)
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 A.  The pressure switch in the water pressurization system is operated by air pressure and starts the air compressor when system pressure drops to 30 psi or less. The pressure switch, when operated, completes a circuit to the compressor relay which, in turn, actuates to complete the power circuit to the air compressor. When system pressure is raised to approximately 40 psi, the pressure switch opens to de-energize the relay and compressor.
Compressor Relay (Fig. 2)
________________
 A.  The compressor relay in the air compressor power circuit controls the operation of the air compressor. The compressor relay, when energized, completes the power circuit that operates the air compressor. The compressor relay is energized when the pressure switch in the water pressure system operates.
Compressor/Bleed Air Interlock Switch (Fig. 1 and 2)
_____________________________________
 A.  The compressor/bleed air interlock switch (interlock switch) is installed on the water service panel. The switch is a plunger-operated unit which controls the overflow/depressurization valve and the compressor. The switch operates when the door for the water service panel is opened or closed.
 (1)  
When the door is opened, the interlock switch causes the overflow/depressurization valve to move to the fill position and also prevents compressor operation.

 (2)  
When the door is closed, the interlock switch causes the overflow/depressurization valve to move to the flight position and also gets electrical power to the compressor.

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MAINTENANCE MANUAL

PRESSURE SWITCH

Potable Water System Pressuization - Component Location
Figure 1

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115V AC GROUND SERVICE BUS
COMPRESSOR MOTOR

P414 PANEL

SYSTEM
P180 PANEL
PLUNGER

Air Compressor Control Circuit Simplified Schematic
Figure 2

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RESET PRESSURE 53 TO 55 PSI
Water System Pressurization Flow Diagram
Figure 3

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 6.  In-Line Air Filter (Fig. 1 and 3)
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 A.  An in-line air filter that has a 10-micron cellulose-aluminum element is installed in the air pressure supply line from the pneumatic manifold.
 7.  Check Valve (Fig. 1 and 3)
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 A.  The check valves keep the flow of air or water from the components upstream from the tanks (Fig. 1 and 3). The unloader check valve also releases the air pressure in the compressor outlet line while the compressor gets up to operational speed.
 8.  Pressure Relief Valve (Fig. 1 and 3)
_____________________
 A.  The pressure relief valve prevents damage from too much pressure in the water system. The pressure relief valve is set to relieve at approximately 60 psi and resets itself at approximately 54 psi.
　
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