Free Pump Affinity Laws Calculator
Calculate new pump performance (flow, head, power) when speed or impeller diameter changes using the affinity laws.
New Flow Rate (Q2)
120.7 m³/h
New Flow Rate (Q2) vs Original Flow Rate (Q1)
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.
Example Calculation
A pump at 1450 RPM delivers 100 m³/h at 30 m head, consuming 15 kW. Speed increased to 1750 RPM.
- 01Speed ratio = 1750 / 1450 = 1.2069
- 02Q2 = 100 × 1.2069 = 120.7 m³/h
- 03H2 = 30 × 1.2069² = 30 × 1.4566 = 43.7 m
- 04P2 = 15 × 1.2069³ = 15 × 1.7581 = 26.37 kW
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