Suppose the pilot controller for the illustrated pneumatically operated diaphragm actuated control valve is supplied with 20 psig control air and is designed to operate the valve with a pilot pressure ranging from 3 to 15 psig. What would be the indication of a properly adjusted spring (6) by means of the adjusting nut (12)? Illustration GS-0051

Correct Answer: Option A — The valve should indicate fully open at 3 psig and should indicate fully closed at 15 psig.

In a standard pneumatic control valve, the spring range defines the operating span. A 3-15 psig signal is the industry standard for pneumatic actuators. At 3 psig, the actuator overcomes the spring to begin opening the valve, reaching the fully open position at the lower end of the signal range.