Pump Affinity Calculator — Formula
## Pump Affinity Laws
The affinity laws predict how centrifugal pump performance changes with rotational speed or impeller diameter. They are essential for variable-speed pump sizing.
### Speed Change Laws
**Q2/Q1 = N2/N1** (flow scales linearly)
**H2/H1 = (N2/N1)²** (head scales with speed squared)
**P2/P1 = (N2/N1)³** (power scales with speed cubed)
The same relationships apply for impeller diameter changes (replacing N with D). The cubic power relationship makes VFDs very effective for energy savings.
The affinity laws predict how centrifugal pump performance changes with rotational speed or impeller diameter. They are essential for variable-speed pump sizing.
### Speed Change Laws
**Q2/Q1 = N2/N1** (flow scales linearly)
**H2/H1 = (N2/N1)²** (head scales with speed squared)
**P2/P1 = (N2/N1)³** (power scales with speed cubed)
The same relationships apply for impeller diameter changes (replacing N with D). The cubic power relationship makes VFDs very effective for energy savings.
Esempio Risolto
A pump at 1450 RPM delivers 100 m³/h at 30 m head, consuming 15 kW. Speed increased to 1750 RPM.
- Speed ratio = 1750 / 1450 = 1.2069
- Q2 = 100 × 1.2069 = 120.7 m³/h
- H2 = 30 × 1.2069² = 30 × 1.4566 = 43.7 m
- P2 = 15 × 1.2069³ = 15 × 1.7581 = 26.37 kW