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Understanding a pump curve is essential when it comes to choosing the best pump for a specific application. By selecting the right pump from the beginning, you can maximise efficiency and extend the pump’s operational life.

A pump curve is a graph that shows the performance characteristics of a pump, usually based on manufacturer standards and testing. It primarily illustrates the relationship between the flow rate and the head with one pump often having several different curves, each usually corresponding to a different impeller size or pump speed.

To understand how a pump curve works, we must first define two key concepts: flow/capacity and head.

A graph displaying pump curves.

A graph displaying pump curves. Image credit: Kelair Pumps

Flow refers to the rate at which a pump can move fluid, often measured in litres per minute (lpm) or cubic metres per hour (m3/h). It represents how much fluid is being moved by the pump over a certain period. As viscosity varies with different liquids, it is important to know what the flow rate is.

Head is defined as the height to which a pump can raise liquid. It’s a measure of the pressure generated by the pump and is normally measured
in metres. The head represents the energy imparted to the fluid by the pump to overcome gravity, friction and any other resistance in the system.

On a pump curve, flow rate is usually plotted on the horizontal axis while
the head is plotted on the vertical axis. The curve usually starts at the highest point on the left, representing the maximum head (pressure) the pump can achieve when there is no flow. As the flow increases, the head the pump can generate decreases.

The point on the curve where the pump operates most efficiently is called the Best Efficiency Point (BEP).

Operating at, or as close to, the BEP as possible is ideal for the longevity and energy efficiency of the pump.

A curve can also include additional information such as efficiency, power consumption and required Net Positive Suction Head (NPSH):

  • Efficiency curves: these are often plotted on the graph as contours or separate lines that peak at the pump’s BEP
  • Power consumption: alongside the main curve, there may be lines indicating the power the pump uses at different flow rates (usually measured in kW or HP)
  • NSPH required: this line shows the minimum pressure required at the suction port of the pump to keep the liquid from vaporising, which can cause cavitation and pump damage.

Understanding a pump curve is crucial for selecting the right pump for a specific application. It shows how the pump will perform throughout its range and is useful for troubleshooting pump performance issues.

Ensuring you have the right pump for the right application involves a thorough set of considerations. Consult a knowledgeable pump supplier like Kelair Pumps to discuss your pumping requirements.

Article courtesy of Kelair Pumps Australia “When Pump Knowledge Matters” Phone 1300 789 466, or visit www.kelairpumps.com.au

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