The pneumatic circuit shown in the illustration is part of a complex large low-speed engine control system. Which of the following statements describes the function of this circuit? Illustration MO-0117

Correct Answer: Option C — Valve D, when depressed, allows the retained pneumatic pressure within the shutdown servomotor to be relieved.

Pneumatic shutdown servomotors rely on maintained control air pressure to hold the fuel linkage in the stop position. Depressing the manual reset or release valve vents this trapped pneumatic pressure, permitting the actuator to return to the normal running position and re-engage fuel injection.