🔍 Key Concepts

• Study how the spring is arranged relative to the diaphragm and stem – which way will it push the stem if no air pressure is applied? • Trace the air line from the pilot valve to see whether pilot pressure is applied to the top or bottom of the diaphragm chamber in this particular drawing. • Think about the fail-safe position of the control valve (what position it goes to on loss of air) and relate that to which force must be the valve opening or closing force.

💭 Think About

• If the spring pushes the stem in one direction, does that move the plug toward the seat (closed) or away from the seat (open)? • When pilot pressure is increased on the side of the diaphragm shown, will the diaphragm deflect to move the stem up or down, and does that correspond to opening or closing? • Compare what happens with spring only versus spring plus pilot pressure – which one opposes the other?

✅ Before You Answer

• Verify from the illustration which side of the diaphragm the pilot pressure connection actually enters – top cavity or bottom cavity. • Confirm whether moving the stem downward seats the plug tightly against the port (valve closed) or lifts it away (valve open). • Make sure your chosen option matches both: spring direction (opening vs closing) and the correct location of pilot pressure (top vs bottom of diaphragm).