What is a pump curve?
Find out what a pump curve is, how it can be used and what it measures.
In order to get the most out of your pumps, it is important that you know how they perform best. And to know this, you need to be familiar with pump curves.
In this module, we’re going to introduce you to pump curves and take a look at what they are used for. Let’s get started.
In simple terms, a pump curve is a graphical representation of the performance of a pump. It provides you with information of several elements of a pump’s performance, helping you identify and select the right pump for your needs.
Pump curves vary from pump to pump, and the variations depend on many factors including the electrical power as well as the size and shape of the impeller.
In its simplest form, pump curves show the flow (Q) and head (H) of the pump. Flow is the rate at which water must be moved throughout a hydraulic system, while head denotes the height at which a pump can raise water up.
Now, let’s take a brief look at some of the most common types of pump curves.
- The QH-curve
- The ŋ-curve
- The P2-curve
- And the NPSH-curve
The QH-curve shows the head that a pump is able to perform at a given flow. Typically, this is measured in metres. One of the advantages of measuring the head in metres is that the QH-curve is unaffected by the density of the liquid it has to handle. In a typical QH-curve for a centrifugal pump, low flow results in a high head, and high flow results in low head.
The ŋ-curve, on the other hand, measures the pump’s efficiency. Efficiency is the relation between the hydraulic power supplied and the power that is used. The efficiency depends on the pump’s duty point, underlining the importance of selecting a pump that fits the flow requirements to ensure that it is always working in the most efficient flow area.
Next, there’s the P2-curve. The P2-curve measures the relation between a pump’s power consumption and flow. For most centrifugal pumps, the P2 value increases when the flow increases.
Finally, there’s the NPSH-curve. NPSH stands for net positive suction head and denotes the minimum absolute pressure that must be present at the suction side of a pump to avoid cavitation.
Cavitation is when small steam bubbles appear in the pump due to the pressure being too low. This can cause damage to the pump.
The NPSH value is measured in metres and is dependent on flow. When the flow increases, so too does the NPSH value.
That covers our basic introduction to pump curves. Thank you for watching.