headcurve

A headcurve, often called a pump head curve or simply a head curve, is the graphical representation of a pump’s hydraulic head as a function of flow rate. It is used to predict the operating conditions of a pump in a system by plotting head (H) versus flow (Q). The vertical axis shows head, typically measured in meters or feet of water, and the horizontal axis shows flow rate in units such as cubic meters per second or gallons per minute. For most centrifugal and axial pumps, the curve slopes downward: as flow increases, the head the pump can impart declines.

The headcurve depends on pump design and operating speed. Increasing shaft speed generally raises the entire curve, producing higher head at all flow rates, and can alter efficiency. The curve is usually obtained from manufacturer test data or validated in the field, and it may be provided for different impeller sizes or speeds.

In system design, the headcurve concept is paired with the system head curve, which describes how much head is required by the piping system at a given flow, often influenced by friction losses and fittings. The operating point of the pump in the system is found at the intersection of the pump headcurve and the system headcurve. The shut-off head is the head at zero flow, while the best efficiency point identifies where the pump operates most efficiently.

Applications include selecting an appropriate pump, estimating energy consumption, and analyzing performance under varying operating conditions. Limitations arise from real-world factors such as viscosity, temperature, altitude, wear, and controls that can shift curves over time.