What percentage of rated capacity must the pumping system deliver at 250 psi net pump pressure?

• A. 70 percent
• B. 50 percent
• C. 100 percent
• D. 80 percent

Answer: (B)

When a pump is tested, its ability to deliver flow depends on the pressure it must overcome. The rated capacity is the maximum flow the pump can provide at low head. As head increases, flow falls along the pump’s performance curve. At a net pump pressure of 250 psi, the curve shows roughly half the rated capacity, so the pumping system should deliver about half of its rated capacity. This reflects the reality that higher pressure reduces flow due to head losses in hose and fittings and the limits of the pump’s efficiency. Delivering more than half would imply unrealistically high flow for that pressure, while much less would indicate a loss of performance.