Flow ∝ N; Head ∝ N²; Power ∝ N³ for a given pump with speed change (or geometrically similar impeller-diameter change).
Formula
$$ \frac{Q_2}{Q_1} = \frac{N_2}{N_1}, \quad \frac{H_2}{H_1} = \left(\frac{N_2}{N_1}\right)^2, \quad \frac{P_2}{P_1} = \left(\frac{N_2}{N_1}\right)^3 $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $N_1, N_2$ | Speeds | rpm | nameplate |
| $Q_1, Q_2$ | Flows | m³/h | pump curve |
| $H_1, H_2$ | Heads | m | pump curve |
| $P_1, P_2$ | Shaft powers | kW | derived |
Sources
- Hydraulic Institute Affinity Laws.