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The second pump affinity law deals with fluid head. The head that a particular pump generates varies with the square of the proportional speed[GS1]  changespeed change. For head, when the impeller speed is increased by 10%, the head is increased by 21% and so on. The affinity law equation for head is:

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The third pump affinity law deals with hydraulic power. The power that a particular pump generates varies with the cube of the proportional speed[GS2]  changespeed change, and thus is most impacted by speed adjustments.  The affinity law equation for power is:

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LaTeX Math Block
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P_2 = P_1 \times \left(\frac{N_2}{N_1}\right)^3

 


Using the equations above, a single point or even an entire pump curve can be adjusted to find out how the pump in question will perform at a different speed. This is especially helpful when looking at the possible applicability and benefits of using a Variable Speed Drive.