Figure 4.26. Variable Inlet Guide Vane System.
With the slide valve in the open position, this air (Pm) is
vented overboard, reducing pressure at the top surface of the
diaphragm. Simultaneously, air is being bled overboard through the
open actuator valve; this reduces pressure at the bottom surface of
the diaphragm. This equalization of pressure on both surfaces of the
diaphragm causes it to remain in a neutral position holding the relay
valve in its open position. With the actuator valve open, the
majority of the P3 air that enters the actuator assembly is vented to
the atmosphere. When the P3 pressure is vented, the actuator spring,
located on top of the actuator piston, expands and pushes the piston
downward. This causes the bleed band to open and remain open as long
as the slide valve on the fuel control is in the open position.