Which of the following is a key indicator that a pump is not delivering the expected discharge despite high RPM?

• A. Low discharge pressure
• B. High engine speed with little water flow
• C. Discharge lines drawing air
• D. Clogged nozzle or valve misposition

Answer: (C)

When a pump is turning fast but isn’t delivering the expected discharge, the presence of air in the discharge lines is a key telltale sign. If the discharge lines are drawing air, air is entering the system and creating pockets that prevent water from moving freely. Those air pockets disrupt the flow, cause partial priming or cavitation, and reduce the actual discharge even though the engine is running at high speed. In practical terms, you’ll often see or hear air in the lines, and the flow won’t come up to the expected volume.

Other signs like low discharge pressure or high engine speed with little water flow can occur for reasons unrelated to air entering the discharge path, such as insufficient prime, suction leaks, or a mechanical restriction, and don’t point as directly to air ingress as observing air in the discharge lines itself. Clogged nozzles or mispositioned valves can reduce flow too, but they don’t explain air being drawn into the discharge path, which is the clearest indicator of the problem described.