🔍 Key Concepts

• Identify the function of diaphragm E in this pilot-operated pressure-reducing valve. • Think about how spring F and downstream pressure act on opposite sides of the diaphragm to position the auxiliary (pilot) valve. • Consider what happens to the force balance and flow path if the diaphragm can no longer separate the two chambers because of a large hole.

💭 Think About

• In normal operation, what pressure is applied to the underside of diaphragm E, and how does that pressure affect the position of the pilot valve and main valve? • If diaphragm E develops a large hole, will downstream pressure still be able to act effectively on the diaphragm, or will spring F dominate? What motion does that cause in the stem connected to the auxiliary valve? • When the auxiliary (pilot) valve moves in that direction, does it cause the main valve B to open more, close more, or stay about the same—and how will that affect downstream pressure relative to the set setting?

✅ Before You Answer

• Be clear on which direction the spring F force tries to move the diaphragm and stem, and which direction downstream pressure pushes. • Trace the flow path from inlet through the main valve B and the pilot passages to see how opening the pilot valve changes pressure above/below the main valve piston. • Verify whether a failed diaphragm would make the regulator go wide open or fail-closed, and then match that behavior to the listed consequences.