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Plant Engineering Calculator

Pump Impeller Trim Calculator — Flow, Head & Power Affinity

Estimate a preliminary trimmed-impeller operating point from diameter ratio using pump affinity relationships for flow, head and power.

Inputs

Results

Diameter ratio 0.900
Estimated flow 180.00 m³/h
Estimated head 48.60 m
Estimated power 32.81 kW
Power change 27.1 %

Formula

r=D2/D1; Q2=Q1r; H2=H1r²; P2=P1r³.

Worked example

Trimming a 250 mm impeller to 225 mm gives r=0.90, screening flow at 90%, head at 81% and power at 72.9% of the reference point.

Assumptions & limits

  • Affinity scaling is an approximation; actual trimmed curves must come from the pump manufacturer.
  • Large trims can materially change efficiency, NPSH and curve shape.

FAQs

What does this Pump Impeller Trim Calculator calculate?

Estimate a preliminary trimmed-impeller operating point from diameter ratio using pump affinity relationships for flow, head and power.

What should I verify before using the result?

Check units, operating point, measured site data and OEM limits. This calculator is a transparent screening tool, not a substitute for equipment selection or code-required design.

Why are intermediate results included?

Intermediate values expose the engineering chain so you can audit assumptions, compare scenarios and catch unrealistic inputs.

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Last updated: 2026-09-17