🔍 Key Concepts

• Pneumatic diaphragm actuator – which part actually moves the stem when air pressure changes? • Difference between process (controlled) fluid flowing through the valve body and the control air going to the diaphragm chamber • How force is created: pressure × diaphragm area gives the closing or opening force

💭 Think About

• Trace the path of the small external line going to the top diaphragm chamber in the illustration. Which medium is entering there, and what is it called in a pneumatic control system? • Ask yourself: does the stem move because of the liquid/gas flowing through the valve body, or because of the air signal applied above the diaphragm? • Look at which component only transmits motion (linkage/plunger) versus which component actually provides energy to push the plug against the seat.

✅ Before You Answer

• Be sure you can distinguish process fluid pressure (inside the large lower body marked INLET/OUTLET) from the pneumatic signal/air supply (small top connection). • Confirm which option’s wording best matches the name for the air pressure used to load the diaphragm in standard pneumatic control terminology. • Eliminate any answers that only describe a part of the linkage (plunger, stem, diaphragm tension) and not the actual energy source that does work to close the valve.