Another source indicates for a pump with a design flow rate of 40 m3/h, a change in speed from 3550 to 1740 rpm resulted in a drop in NPSHR from 2.5 to 1 m, while for a pump with a flow rate of 600 m3/h between 1770 and 1175 rpm, the NPSHR drop was from 4 m to 2.4 m.
Applying the suggested formulas, the resulting exponents are even more "conservative" (lower than 1.3) than those indicated by bradshsi when reducing speeds.
Therefore, assuming all sources are correct, the conclusion should be...
Not being an expert on centrifugal pumps, just a user, my question is: for the same pump why should the exponents differ when increasing or decreasing the rotating speeds ?