How Pump Affinity Laws Change Flow, Head, and Power
Quand cela s’applique
Use this guide for rapid what-if checks on variable-speed operation, while being explicit that affinity laws are approximations around similar hydraulic conditions.
Outil à utiliser
Faire varier debit, hauteur et puissance selon la vitesse de pompe.
Ouvrir Calculateur de lois d'affinite pompe →Étapes
- 1Start from a known operating point (Q1, H1, P1, N1) on the same pump and impeller.
- 2Set target speed N2 and compute speed ratio r = N2/N1.
- 3Scale flow, head, and power with Q2 = Q1*r, H2 = H1*r^2, P2 = P1*r^3.
- 4Compare scaled point against system curve and motor limits.
- 5Treat the result as screening, then verify with vendor data.
Exemples
- Estimating energy impact of reducing speed from 50 Hz to 45 Hz.
- Checking whether a small speed increase could recover required head.
Ce qu’il faut éviter
- Applying affinity laws across very large speed changes without validation.
- Ignoring NPSH and motor current constraints.
- Assuming efficiency stays constant for all operating points.
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FAQ
Do affinity laws replace pump curves?
No. They provide first-order scaling and should be checked against manufacturer performance data.
Can I use this for impeller trim and speed changes together?
Use caution; combined effects need proper vendor-supported methods.