Rules for PRV block valves require them to be in which state?

• A. Must be 100% open or closed
• B. Must be variable between open and closed
• C. Must be halfway open
• D. Must be fully closed at all times

Answer: (A)

The key idea here is that a PRV (pressure relief valve) block valve must have a definite position—either fully open or fully closed. In normal operation, the block valve should be fully open so there’s no flow restriction that could affect the relief system’s response. When maintenance or isolation is needed, it should be fully closed to guarantee a tight seal and prevent any bypass or leakage around the relief line. Keeping the valve partially open or at an intermediate position can allow leaks, create improper isolation, and complicate the PRV’s functionality. So, the required state is for the block valve to be either fully open or fully closed.