Assuming that the flow is from left to right on the illustrated pneumatically-operated diaphragm-actuated control valve, what statement is true? GS-0051

Correct Answer: Option B — Inlet pressure acts on the lower surface of the top disc and the upper surface of the bottom disc for the purpose of achieving hydraulic balance so that inlet pressure does not influence the valve position.

In a double-seated valve, inlet pressure acts on the lower surface of the top disc and the upper surface of the bottom disc. Because these forces are equal and opposite, the valve is hydraulically balanced, meaning the inlet pressure does not exert a net force on the valve stem.