When the solenoid is not energized, chamberB is vented to ambient pressure and thevalve sleeve remains in the closed position.To activate the system, the solenoid is en-ergized, which enables reference control airpressure to reach chamber B to overcome sleevespring force and start to open the valve sleeve.If the inlet pressure is only ambient pressure, thesleeve remains fully closed. A 2 psi marginof inlet pressure over outlet pressure starts thesleeve opening action. When inlet pressure reaches30 psi absolute (psia) and outlet pressure isat the 26±2 psia setpoint, the valve sleeveopens. Further increase of inlet pressure,which would otherwise cause an increasein outlet pressure, is sensed in chamber A,which adds to the closing force of the valvesleeve. As the valve sleeve moves toward amore closed position, the outlet pressure isreduced and the 26±2 psia setpoint is main-tained. Continued increase of inlet pressureresults in continued valve sleeve closure untilthe pressure regulator valve is completelyclosed, thereby preventing outlet pressure fromexceeding 28 psia.Bleed-Air Solenoid ValveEight cyclic valves are used in the deice system.Two cyclic valves are located in each outboardwing, one in each inboard wing, and one in eachhorizontal stabilizer. The cyclic valve is normallyspring-loaded closed, electrically controlled, andpneumatically actuated. The cyclic valve controlsthe cyclic distribution of bleed air to theappropriate segment of the deice system piccolotubes.The cyclic valve is pneumatically controlledby a bleed-air solenoid valve (fig. 1-13). When thesolenoid is not energized, the spring keeps thecyclic valve closed, and inlet pressure is ventedto ambient and to the closing side of the valve(chamber A). When the solenoid is energized, theinlet pressure is blocked, and when it builds toFigure 1-13.—Bleed-air solenoid valve.1-16
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