🔍 Key Concepts

• Diaphragm-operated pressure-reducing valve: outlet (downstream) pressure is sensed under the diaphragm and balanced against the adjusting spring force above it. • Spring vs. pressure balance: the spring force tends to move the stem in one direction (usually to open the valve), while outlet pressure acting on the diaphragm tends to move it in the opposite direction (to close the valve). • Fail-safe behavior and setting changes: consider what normally happens to outlet pressure if you tighten (compress) the adjusting spring, and what a diaphragm rupture would do to that balance.

💭 Think About

• Look at the illustration and decide: does the adjusting spring push the stem downward or upward, and in which direction must the stem move for the valve to open wider? • If the outlet (downstream) pressure drops, what happens to the upward force on the diaphragm? Then, which way will the spring move the stem? • When you compress the adjusting spring more with the handwheel, are you telling the valve to maintain a higher or lower outlet pressure? How does that affect which answer choices can be true?

✅ Before You Answer

• Be clear which side of the diaphragm senses outlet pressure and which side contains the spring in the figure. • Verify the direction of motion for opening vs. closing the main valve in the sketch (which way must the stem move to increase flow?). • Double-check your understanding that tightening (compressing) the adjusting spring raises the set outlet pressure, not lowers it, and use that to rule out at least one option.