Pump Affinity Calculator

Calculate new pump performance (flow, head, power) when speed or impeller diameter changes using the affinity laws.

m³/h
m
kW
RPM
RPM

New Flow Rate (Q2)

120.7 m³/h

New Head (H2)43.7 m
New Power (P2)26.37 kW

New Flow Rate (Q2) vs Original Flow Rate (Q1)

Vedi formula →

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.

Esempio Risolto

A pump at 1450 RPM delivers 100 m³/h at 30 m head, consuming 15 kW. Speed increased to 1750 RPM.

  1. 01Speed ratio = 1750 / 1450 = 1.2069
  2. 02Q2 = 100 × 1.2069 = 120.7 m³/h
  3. 03H2 = 30 × 1.2069² = 30 × 1.4566 = 43.7 m
  4. 04P2 = 15 × 1.2069³ = 15 × 1.7581 = 26.37 kW