🔍 Key Concepts

• Pneumatically controlled steam pressure reducing valve – how air pressure, steam pressure, and the pilot valve interact • Difference between a control problem (signal/pilot) and a capacity/pressure problem (spring, supply pressure) • How a defective pilot or control signal typically shows up as hunting or erratic movements

💭 Think About

• Ask yourself: which option is most likely to cause rapid, hunting, or unstable motion rather than a steady but wrong outlet pressure? • Think about how the pneumatic signal reaches the main valve: what small device actually converts the air control signal into movement of the main valve? • Which choice would mainly limit or shift the pressure range in a stable way, and which would cause the valve to keep over‑correcting back and forth?

✅ Before You Answer

• Identify which part of the system directly modulates the main valve in response to small changes in pneumatic signal. • Decide which fault would cause hunting/oscillation (erratic operation) rather than simply a low or high but stable outlet pressure. • Check whether insufficient steam supply pressure would make the valve behave erratically, or just prevent it from reaching the set outlet pressure in a predictable way.