What the Pump Was Designed to Do and Why it Doesn’t Do It
Contrary to popular opinion, a centrifugal pump is not designed to develop one head at a single capacity as requested by the pump purchaser. In fact a pump is designed and produced to supply a whole range of head-capacity conditions as identified on it’s performance curve. The pump will operate on that curve if it is driven at the particular speed for which the curve is drawn.
However, the actual conditions on that curve at which the pump will run, will be determined by the system in which it operates. In other words, for all practical purposes, the system controls the pump, and will operate that pump at whatever conditions it sees fit, regardless of the Head and Capacity for which it was bought (and designed) to achieve.
First we need to understand how a pump works!
For this we need to understand the Characteristic Pump Performance Curve. To the uninitiated, this diagram may seem like a mass of lines set up simply to confuse the reader. In fact, it is only a picture of how the pump works. However, we do need to be able to make some sense out of that picture
Click here to view the full pdf.