by Joe Evans
December 29, 2012
Figure 2. Relationship for a 10-horsepower motor and the same pump shown in Figure 1

The ratio of available motor HP to required pump HP increases exponentially as speed is reduced. Figure 2 shows this relationship for the same pump and a 10-HP motor. Here, the available HP does not meet the required HP until the speed is below 50 Hz. If the reader’s design point could have been met at 45 Hz, the 10-HP motor would have been adequate. The calculator that produced Figures 1 and 2 is available on the “Pump Evaluation, Selection & Testing Tools” on my website.

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