BETA

Affinity Laws Calculator

Estimate pump performance changes when speed or impeller diameter changes.

Calculator

Calculation mode

Initial flow rate Q₁

Initial head H₁

Initial power P₁

Initial speed N₁

rpm

New speed N₂

rpm

Ratio —

New flow rate Q₂ —

New head H₂ —

New power P₂ —

Formula

For speed change, the affinity laws are:

Q₂ = Q₁ · (N₂/N₁)

H₂ = H₁ · (N₂/N₁)²

P₂ = P₁ · (N₂/N₁)³

Beta limitation:

Works best for small changes near the same pump curve.
Impeller trim calculations are approximate.
Efficiency may change.
NPSHr and minimum flow must be checked separately.

Engineering note

Affinity laws are useful for quick estimates, but final pump selection must be verified against the real pump curve, efficiency, NPSH, minimum flow, motor power and manufacturer limits.

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