Dimensionless ratio that characterises pump type. Low Ns (< 25) = radial; mid (25–50) = mixed flow; high (> 50) = axial.
Formula
$$ N_s = \frac{N \cdot \sqrt{Q}}{H^{3/4}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $N$ | rpm | rpm | nameplate |
| $Q$ | Flow at BEP | m³/s | pump curve |
| $H$ | Head at BEP | m | pump curve |
Sources
- Hydraulic Institute ANSI/HI 9.1-9.5.