What is the purpose of a pump min-flow line?

• A. To protect the pump from operating at deadhead
• B. To measure flow
• C. To vent air
• D. To recirculate to the suction side

Answer: (A)

A pump min-flow line is there to keep the pump from running with almost no flow, which is known as deadheading. When flow through the pump drops to near zero, cooling and lubrication through the liquid become insufficient, and the impeller, seals, and bearings can overheat, wear, or be damaged. By diverting a small portion of the pumped fluid back to the suction side (or to a reservoir), the pump always has a minimum amount of flow. This maintains cooling, reduces vibration, and protects against damage and cavitation, even when system demand is low. It isn’t meant for measuring flow or venting air; the essential purpose is to ensure safe, continuous operation by preventing deadhead.