A pump is delivering less than the expected rate of discharge. Which condition is most likely causing this?

A pump is delivering less than the expected rate of discharge. Which condition is most likely causing this?

• A. Discharge head too low
• B. Discharge head too high
• C. Check valve open
• D. Pump is primed

Answer: (B)

When a pump delivers less than the expected discharge, the most likely reason is that the discharge head is too high for the pump to overcome at the desired flow. The pump’s performance curve shows that as the head (the pressure the pump must push against in the discharge line) increases, the flow rate decreases. If the system has more head—due to a long pipe run, higher elevation, or additional valves and fittings—the pump must work harder, so the actual discharge drops. If the discharge head were too low, you'd typically see more flow, not less. A check valve being open is normal for allowing flow; if it were stuck closed or partially closed, it could reduce discharge, but that’s not the stated condition. A primed pump means it's ready to pump; if it were unprimed, flow would be minimal or nonexistent. Hence, high discharge head best explains the reduced discharge.

When a pump delivers less than the expected discharge, the most likely reason is that the discharge head is too high for the pump to overcome at the desired flow. The pump’s performance curve shows that as the head (the pressure the pump must push against in the discharge line) increases, the flow rate decreases. If the system has more head—due to a long pipe run, higher elevation, or additional valves and fittings—the pump must work harder, so the actual discharge drops.

If the discharge head were too low, you'd typically see more flow, not less. A check valve being open is normal for allowing flow; if it were stuck closed or partially closed, it could reduce discharge, but that’s not the stated condition. A primed pump means it's ready to pump; if it were unprimed, flow would be minimal or nonexistent. Hence, high discharge head best explains the reduced discharge.