757 AMM 飞机维护手册 空调 AIR CONDITIONING 1(162)

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 6)  The pressure in chamber M is supplied by the throat-pressure-sensing-probe. As the butterfly plate opens, the pressure in the throat, and in chamber M, decreases. Thus, the diaphragm moves off of the plate valve to let air from chamber C flow into chamber D.
 7)  The pressure in chamber C is supplied by the inlet pressure sensing probe. However, the amount of pressure supplied to chamber C is controlled by the adjustable orifices. Usually, the pressure is supplied through the adjustable orifices E and F. But the pressure changes when these orifices are closed or other orifices are opened.
 8)  When the throat pressure decreases, the inlet pressure also decreases a specified amount. Because the inlet pressure is a proportion of the throat pressure, the differential pressure between chamber M and chamber C does not change frequently. Thus, the butterfly plate will not have to make as many movements.
 (d) The high flow mode 1) The flow-control-and-shutoff valve will go to the high flow mode when the solenoid B is open and solenoid A is open. The solenoid B must always be open for the flow-control-and-shutoff valve to be open. If solenoid B is closed, the valve will be closed.
 2)  Solenoid A is open when it is energized. When solenoid A is energized, it moves the actuator rod to move the ball in the ball valve assembly.
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757 MAINTENANCE MANUAL
 3)  When the ball in the ball valve assembly is moved, it closes the bleed port from the adjustable orifice F. Then the only air that is supplied to chamber C, is the air through orifice E. Thus, the pressure in chamber C is decreased. With the pressure in chamber C decreased, the bleed nozzle port will stay closed longer and the butterfly plate will open more.
 4)  Also, the air flow rate in the high flow mode can be adjusted by the supply bleed nozzle (see the electro-magnetic-control valve paragraph).
 (e) Changes in the altitude 1) The altitude is sensed by the pressure sensor in the slave servo valve. As the altitude increases, the aneroid expands. As the aneroid expands, it increases the pressure of the spring on the actuator lever assembly. However, the pressure in chamber Q decreases. Thus, when the altitude is below 22,000 feet, an altitude change will not change the force on the actuator lever assembly.
 2)  When the altitude is greater than 22,000 feet, the aneroid comes against the altitude adjustment H. Thus, the aneroid cannot expand any more. But the pressure in chamber Q continues to decrease. This lets the pressure in chamber D move the actuator lever assembly to open the bleed nozzle port. As the bleed nozzle port opens, the pressure in the pneumatic actuator decreases and the butterfly plate becomes less open. Thus, the air flow rate changes so that the mass of the air will be decreased but the volume will stay the same.
 (f) Changes in the electro-magnetic-control-valve current 1) Changes in the electro-magnetic-control-valve current will only change the air flow rate when the flow-control-and-shutoff valve is in the high flow mode.
 2)  The applicable (left or right) automatic-pack-temperature controller supplies the electrical current to the torque motor of the electro-magnetic-control valve. The torque motor controls a flapper which closes the supply nozzle port. When 28v dc power is supplied to the torque motor, the flapper closes the supply nozzle port. As the current decreases, the torque motor moves the flapper away from the supply nozzle. This opens the supply nozzle to let air flow through the adjustable orifice G to solenoid A. If solenoid A is open (the high flow mode) the air can flow into chamber C. As the supply nozzle opens more, the pressure in chamber C will increase more. As the pressure in chamber C increases, the butterfly plate becomes less open.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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757 MAINTENANCE MANUAL
 (g)  
The closed mode

 1)  The flow-control-and-shutoff valve will be closed when the solenoid B is closed. The solenoid B is closed when it is momentarily energized to the closed position and it is not manually opened. When solenoid B is closed, the manual control rod is moved so that the ball valve assembly can seat. This closes the bleed port to the solenoid-B-inlet connection so that no air can enter the ball valve assembly Thus, no air can flow to the pneumatic actuator and the butterfly plate closes.
　
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