Which of the following is the correct method to perform a partial flow test of a master pressure reducing valve?

• A. Closing the main shut off valves.
• B. Main drain test on a quarterly basis.
• C. Opening the inspectors test valve annually.
• D. Turning the fire pump on and opening the case relief valve.

Answer: (B)

Partial flow testing a master pressure reducing valve checks how well the valve reduces downstream pressure when only part of the system is drawing water. The correct approach uses the main drain valve to create a controlled, partial discharge through the PRV. By opening the main drain, you simulate a partial demand and can observe the valve’s ability to hold the downstream pressure within the expected range without draining the entire system. Performing this test on a quarterly basis provides regular confirmation that the PRV continues to operate correctly under typical partial-flow conditions.

Closing the main shut-off valves would stop flow entirely, so you wouldn’t be testing the valve’s behavior under partial demand. Opening the inspector’s test valve annually is a separate test related to the valve’s testing arrangement but does not constitute the standard partial-flow verification. Turning the fire pump on and opening the case relief valve introduces pump-related actions and relief venting and does not specifically test the master PRV’s partial-flow performance.