After changing the speed of the centrifugal pump...

So, let’s assume that the frequency of an adjustable-speed centrifugal pump is changed from 100 to 50. According to the pattern shown in the diagram above, the flow rate should decrease by half. However, with the operating conditions remaining unchanged, the head of the centrifugal pump should decrease by four times. Once the head decreases, the flow rate should also decrease. If the flow rate becomes half of its original value when the head remains unchanged, then after the head decreases, the flow rate will definitely be less than half of the original value. Wouldn’t that contradict the pattern outlined above? I’m a bit confused about this

This post was last edited by WSRYLONG on 2018-9-17 at 11:47. What the original poster presented is the most common view at present. But in reality, the variation patterns of various parameters in a centrifugal pump after changing its speed are related to the specific speed; different specific speeds result in different variation patterns. Only through a large number of experiments can these patterns be analyzed, discovered, and verified, in order to gain credibility. However, there is a lack of substantial experimental data at present. Although it is important basic research and not difficult to carry out, no one does it. For general-purpose products such as water pumps, which are used in large quantities and consume a lot of electricity, it is highly necessary and meaningful to conduct extensive experimental research on their operating patterns and the factors that affect their efficiency. **The industry should provide the funding and resources needed to carry out such research, but currently there is a lack of effort in this area, which is truly regrettable from the standpoint of technological research, progress, and energy conservation.

The formula applies within a specific range, and there’s no problem with that. The operating point is the intersection of the characteristic curve of the piping system and the performance curve of the pump; when the flow rate changes, the characteristic curve of the piping system also changes.

Head is head, and flow rate is flow rate{:3_52:}

What changes after frequency conversion is the pump’s characteristic curve. The operating point of the pump is determined by the device’s characteristic curve.