Suppose the illustrated self-contained, internal-pilot, piston-operated steam pressure- reducing valve is part of a 600-to150 psig reducing station. If there was an increase in demand for steam downstream, what statement correctly represents how the valve would initially respond? GS-0044

Correct Answer: Option B — The downstream pressure would drop, causing the control diaphragm to flex downward and further open the pilot valve.

Increased downstream demand lowers pressure beneath the control diaphragm. This pressure drop allows the spring force to flex the diaphragm downward, opening the pilot valve. This action increases steam flow to the main piston chamber, which subsequently opens the main valve to restore the set downstream pressure.