Pump - Affinity Law

Centrifugal-pump performance scaling when impeller speed or diameter changes - Q ∝ n, H ∝ n², P ∝ n³.

PumpAffinityCentrifugal

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Formula, assumptions, and limits

\frac{Q_2}{Q_1} = \frac{n_2}{n_1}, \ \frac{H_2}{H_1} = \left(\frac{n_2}{n_1}\right)^2, \ \frac{P_2}{P_1} = \left(\frac{n_2}{n_1}\right)^3

Symbol	Meaning	Unit
$Q, H, P$	Flow, head, power
$n$	Impeller speed	rpm

Source: Hydraulic Institute Standards

Centrifugal-pump performance scaling when impeller speed or diameter changes - Q \u221d n, H \u221d n\u00b2, P \u221d n\u00b3.