An engineer would expect a relief valve to start function at a pressure:

• A. Operating pressure
• B. Design pressure
• C. Maximum pressure
• D. Minimum pressure

Answer: (B)

Relief valves are set to protect the system at the pressure the equipment is designed to handle. This setpoint, called the design pressure, defines the maximum safe pressure for normal operation with an appropriate safety margin. Opening at the design pressure means the valve vents before the pressure climbs into unsafe territory, preventing damage to components and piping.

If the valve opened at operating pressure, it would vent during normal use, causing nuisance loss. Opening at the maximum pressure would allow the system to reach a potentially unsafe level before relief kicks in. Opening at minimum pressure doesn’t make sense for overpressure protection. So the best choice is design pressure, ensuring protection exactly at the level the system is designed to tolerate.