Bleed-Air Solenoid Valve

When the solenoid is not energized, chamber B is vented to ambient pressure and the valve sleeve remains in the closed position. To activate the system, the solenoid is en- ergized, which enables reference control air pressure to reach chamber B to overcome sleeve spring force and start to open the valve sleeve. If the inlet pressure is only ambient pressure, the sleeve remains fully closed. A 2 psi margin of inlet pressure over outlet pressure starts the sleeve opening action. When inlet pressure reaches 30 psi absolute (psia) and outlet pressure is at the 26±2 psia setpoint, the valve sleeve opens. Further increase of inlet pressure, which would otherwise cause an increase in outlet pressure, is sensed in chamber A, which adds to the closing force of the valve sleeve. As the valve sleeve moves toward a more closed position, the outlet pressure is reduced and the 26±2 psia setpoint is main- tained. Continued increase of inlet pressure results in continued valve sleeve closure until the pressure regulator valve is completely closed, thereby preventing outlet pressure from exceeding 28 psia. Bleed-Air Solenoid Valve Eight cyclic valves are used in the deice system. Two cyclic valves are located in each outboard wing, one in each inboard wing, and one in each horizontal stabilizer. The cyclic valve is normally spring-loaded closed, electrically controlled, and pneumatically actuated. The cyclic valve controls the cyclic distribution of bleed air to the appropriate segment of the deice system piccolo tubes. The cyclic valve is pneumatically controlled by a bleed-air solenoid valve (fig. 1-13). When the solenoid is not energized, the spring keeps the cyclic valve closed, and inlet pressure is vented to ambient and to the closing side of the valve (chamber A). When the solenoid is energized, the inlet pressure is blocked, and when it builds to Figure 1-13.—Bleed-air solenoid valve. 1-16