On a pump curve, which axis represents capacity?

• A. Vertical axis
• B. Horizontal axis
• C. Diagonal axis
• D. Both axes

Answer: (B)

Capacity, which is the flow rate, is plotted on the horizontal axis of a pump curve. The vertical axis shows head (feet of head or pressure). This layout lets you read the flow value along the x-axis and the corresponding head on the y-axis, and to find the operating point you look where the pump curve meets the system curve. There isn’t a diagonal axis used, and capacity isn’t represented on both axes. So the axis for capacity is the horizontal axis.