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Knowing how to read a pump curve is essential to understanding your equipment and being able to troubleshoot issues as they arise. In a previous post, we discussed how to properly read a centrifugal pump curve. Here, we will discuss how to read and understand a positive displacement pump curve.
Before we learn how to read the curves, we have to first understand the how a positive displacement pump operates. A positive displacement pump has an expanding fluid cavity on the suction side of the pump, and a shrinking fluid cavity on the discharge side of the pump. The pumped fluid flows into the cavity as the suction side expands and flows out as the discharge cavity shrinks. Over a complete cycle of the pump, this volume remains constant. The image below shows how this operation happens.
Positive displacement pumps cover a wide range of pumps, including:
These pumps provide a constant flow of fluid at a given pump speed, regardless of the discharge pressure required. A pressure relief needs to be used with these pumps to protect both the pump and the process in which it is installed. If a relief is not provided, the pump will continue to develop pressure until the point that the pump, or the weakest point in the process, is damaged to relieve the pressure. This can be very costly and also very dangerous to anyone working around these pumps.
Enough about the pumps, on to the curves!
The majority of positive displacement pump curves will look like the curve shown below:
Positive displacement pumps can handle many difficult applications. Understanding how to read a positive displacement pump curve can help troubleshoot a currently installed system, or help to size equipment for the next project down the road.
Need further assistance with your pump curves? Ask us about it! We're happy to provide technical assistance to businesses in Wisconsin and Upper Michigan.