If the measured discharge flow does not match the expected value, what is a likely cause to check first?

• A. The relief valve is closed.
• B. The water supply is unlimited.
• C. The pump RPM is too high.
• D. The discharge valve is closed or not fully open.

Answer: (D)

When discharge flow doesn’t meet the expected value, the most likely reason is a restriction in the discharge path. If the discharge valve isn’t fully open (or is closed), it creates a throttle that limits how much water can leave the pump, so the measured flow drops below the pump’s rated capability at the set RPM. This is the first thing to check because it directly controls the amount of water that can be discharged.

Inspect the discharge valve to confirm it’s fully open, and check for any downstream throttling devices or partial obstructions in the discharge line. If the valve is indeed fully open and there are no blockages, then you would look at other factors like the pump RPM or the relief path, but the valve position is the most common, immediate cause of reduced discharge.