A pump curve is the path that a pump has to operate on. In
graph form, it tells us the performance of a pump flow rate versus the head.
The curve is designed by the manufacturer and is based on the horsepower, the
diameter of the impeller and the shape of its volute (the wet end of the pump
that contains the impeller). No matter what the conditions of a system, the
pump has to operate somewhere on this curve. When a piping system is made up
primarily of vertical lift and very little pipe friction, the pump
characteristic should be steep and when a piping system is made up primarily of
friction head and very little of vertical lift, the pump characteristic should
be near horizontal.
System curves, on the other hand, represent the flow-head relationships that exist for particular installations. For any given system, once a design condition is calculated, you can establish other flow and head conditions by scaling the curve. The performance curve states "head will change as the square of the change in flow.
