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Impeller Trimming

A centrifugal pump operates according to its pump curve. The pump will deliver the head and flow specified on its pump curve that intersects with the required head on the system curve. The head curve is for a particular impeller trim running at particular speed (RPM). In some cases, it is desired to modify the impeller to achieve different pump performance, and data at the modified impeller size is not available.

AFT software (AFT Fathom, AFT Arrow, and AFT Impulse) can automatically adjust a pump curve for different impeller trims in a couple of different ways, depending on the user input. If the user specifies multiple pump configurations in the pump curve, the various impeller diameters that were input directly can be selected from the Pump Model window (see Figure 1).

Figure 1 Pump Properties window

Figure 1 - Pump Properties window with multiple speed/impeller diameters input

If information about the trimmed impeller is not known, users can select to modify the input pump curve. In this case, the affinity laws can be used to modify the pump curve to ratio the impeller as either a percent or as an actual impeller size (this input requires multiple configurations to be input).

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