A pump curve is a graphic representation of centrifugal pump performance based on pressure and flow, and indicates at what point the pump is most efficient.
The data is collected by the manufacturer during pump testing, and the pump curve is used by the construction group to choose the right pump for the job.
First, pump flow is charted across the bottom of the chart (x-axis) and the differential pressure is charted on the left hand side (y-axis).
Then the manufacturer typically plots four curves:
- system head
- capacity versus pressure
- capacity versus pump efficiency
- capacity versus input
The system head curve is a function of the static head in the system plus friction losses.
The curves are placed going upwards from left to right (system and power curves); downward from left to right (head curve); and as a bell curve (efficiency).
The point where system head and capacity curves intersect indicates the operating point of the pump.
This point shows the most efficient operation of the pump, and what flow and pressure will be generated there.
Normally the pump motor is sized larger than the most efficient point, as this enables the pump to put out more flow even at less efficiency, when required.
The pump curve chart also notes the rpm of the pump and the size, which is written as three numbers in the form 1-2-3.
- the largest number represents the diameter of the impeller
- the second largest number represents the diameter of the suction port
- the smallest number represents the diameter of the discharge port
By increasing the size of the impeller or by speeding up the pump, the head curve can be moved upwards to change the operating point.
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