The system (fig. 1-12) uses three pressure regulating valves. One pressure regulating valve

Figure 1-11.- Engine anti-icing system.

is located in each engine pylon, and one is located in the forward upper left section of the ECS compartmen. The pressure regulating valve is normally closed, and is electrically controlled and pneumatically actuated. The pressure regulator valve has two functions; to regulate deice air pressure when energized and to shut off deice air when de-energized. The pressure regulator valve functions on differential pressure to maintain an outlet duct pressure of 26 2 psi. Acuation of the pressure regulator valve to the regulating function is accomplished by setting the deice switch on the ENVIRONMENTAL panel on the center console to WING EMP. The pressure regulator valve is normally closed because the valve sleeve is spring-loaded closed. Inlet air pressure (chamber C) is sensed by the control air pressure regulator, which, when the deice system is operating, maintains an output of constant reference pressure to control the opening side of the sleeve (chamber B). Chamber A is the closing side of the valve sleeve and is vented to the pressure regulating valve outlet pressure.

Figure 1-12.- Deice pressure regulating 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.