Pressure is needed to make the liquid flow at the required rate and this must overcome head ’losses’ in the system. These losses can be divided into two types: static and dynamic heads,
The performance of a pump can be expressed graphically as the outlet head against the flow rate produced. The most frequent use of pump curves is in the selection of centrifugal pumps, as the flowrate of these pumps varies dramatically with system pressure,
The system head curve can be plotted on the same axes as the pump curve,
The graph below shows the pump and system curves for an example system.