Which safeguards re-close when the upstream supply pressure subsides?

• A. Check valve
• B. Safety interlock
• C. Gate valve
• D. Pressure relief valve

Answer: (D)

The key idea is automatic reseating after relieving pressure. A pressure relief valve opens to vent when the system pressure exceeds its set limit, and once the pressure falls back to a safe level, it automatically reseats and stops venting. This re-closing behavior is what protects the system from overpressure while avoiding continuous venting.

Other devices don’t match this automatic pressure-based reseating: a check valve lets flow in one direction and mainly prevents backflow, not regulate pressure and reseat after an overpressure event; a safety interlock is a control mechanism that stops a process when a condition is met and doesn’t automatically reclose just from pressure changes; a gate valve is an isolation valve that requires manual or actuator action to close, not a passive response to pressure.