(5)  
The ELEC pump select switch on the hydraulic control panel controls the ACMP. In the ON position the switch energizes the ACMP control relay to supply 28 volts dc to the ACMP electrical load control unit (ELCU). The ELCU relay closes to supply 115/200 volt, 400 Hz, 3-phase power to the pump motor. The pump then supplies fluid flow as demanded by the operating systems. Moving the pump select switch to the OFF position removes power and stops the pump.

 (6)  
If power is lost on the left main AC bus, the right ACMP enable relay opens to de-energize and reset the right ACMP time delay.

 (7)  
The RESERVE BRAKE switch on main instrument panel P1 controls the right ACMP isolation valves (Fig. 16). In the ON position, the switch energizes the reserve brakes control relay to supply 28 volts dc to the supply and pressure shutoff valves. The reserve brakes control relay also energizes the right ACMP control relay to turn on the right ACMP. The supply shutoff valve motor drives the valve to the reserve position which supplies fluid to the right ACMP from the bottom of the reservoir. The pressure shutoff valve motor drives the valve to the closed position. This isolates the right ACMP output to power only the normal brakes. A white ON switch light is illuminated when the switch is in the reserve brake position. EICAS message RSV BRAKE VAL will be displayed while the valves are in transit and when position of either valve does not agree with the switch position.

 (8)  
If left engine power is lost, the right hydraulic system drives a power transfer unit (PTU) to provide left system pressure. For information on the PTU, refer to 29-22-00.

 B.
Functional Description - C System (Fig. 17)

 (1)  
The system reservoir supplies a flow of fluid under pressure to the two ACMP's. The output of the pumps flows through filters in the ACMP filter module before going to the operating systems. Return fluid from the operating systems flows through a filter in the return module before entering the reservoir.

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A
757
MAINTENANCE MANUAL

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 ALL  ú ú 01 Page 25 ú Jan 28/02
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