On a pump performance curve, which parameter is plotted on the horizontal axis, and which are plotted on the vertical axis?

• A. Horizontal: Head; Vertical: Capacity, Power, Efficiency
• B. Horizontal: Efficiency; Vertical: Capacity
• C. Horizontal: Power; Vertical: Head
• D. Horizontal: Capacity; Vertical: Head, Power, Efficiency

Answer: (D)

A pump performance curve shows how a pump’s output parameters change as flow changes. The flow rate, or capacity, is placed on the horizontal axis because it’s the independent variable you vary to see how the pump responds. The vertical axis represents the corresponding values for head (the pressure rise the pump provides) as well as power and efficiency, which are dependent on that flow. This layout lets you compare how head, power, and efficiency behave across the full range of flow. In typical centrifugal pumps, head tends to decrease as flow increases, power increases with flow, and efficiency peaks at a certain point. So the horizontal axis is capacity, and the vertical axis carries head, power, and efficiency.