Calculator Inputs
Enter reference pump data, efficiency assumptions, and a system curve. The calculator adjusts the pump curve with affinity laws, estimates the duty point, and returns a detailed performance table.
Example Data Table
Use this sample set to test the calculator or compare vendor selections quickly.
| Scenario | Shutoff head (m) | Rated flow (m³/h) | Rated head (m) | BEP flow (m³/h) | BEP efficiency (%) | Speed ratio | Impeller ratio |
|---|---|---|---|---|---|---|---|
| Base water transfer | 62 | 160 | 38 | 145 | 81 | 1.00 | 1.00 |
| Trimmed impeller | 62 | 160 | 38 | 145 | 81 | 1.00 | 0.96 |
| Higher speed check | 62 | 160 | 38 | 145 | 81 | 1.08 | 1.00 |
Formula Used
- Base pump curve: H(Q) = H0 − kQn
- Curve constant: k = (H0 − Hr) / Qrn
- Flow scaling: Q2 = Q1(N2/N1)(D2/D1)
- Head scaling: H2 = H1(N2/N1)2(D2/D1)2
- Power scaling: P2 = P1(N2/N1)3(D2/D1)3
- System curve: Hsystem = Hstatic + KQ2
- Hydraulic power: Phyd (kW) = SG × Q × H / 367
- Shaft power: Pshaft = Phyd / ηpump
- Motor input: Pmotor = Pshaft / ηmotor
The efficiency model is an engineering estimate centered on BEP. It is helpful for comparisons, screening, and early sizing, but it does not replace a manufacturer’s certified performance test.
How to Use This Calculator
- Enter shutoff head, rated flow, and rated head from your reference curve.
- Set the curve exponent. A value near 2 often suits centrifugal pumps.
- Enter BEP flow and BEP efficiency from test data or vendor literature.
- Add fluid specific gravity and motor efficiency to estimate power demand.
- Use speed and impeller ratios to simulate VFD changes or trimming.
- Describe the system curve with static head and a quadratic loss coefficient.
- Press calculate to show the duty point, chart, curve table, and export buttons.
- Download CSV or PDF for design notes, reviews, or procurement files.
FAQs
- 1. What does this calculator estimate? It estimates an adjusted pump head-flow curve, the system intersection, efficiency, hydraulic power, shaft power, and motor input for the selected scenario.
- 2. Why is shutoff head higher than rated head? Shutoff head occurs at zero flow. Rated head occurs at a working flow, so centrifugal pumps normally produce less head as flow rises.
- 3. What exponent should I use? Use 2 as a practical starting point for many centrifugal pumps. If you have vendor data, fit the exponent so the estimated curve better matches actual points.
- 4. What is the system coefficient? It represents friction losses that rise with flow squared. Larger coefficients create a steeper system curve and usually reduce the operating flow.
- 5. Can I model impeller trimming? Yes. Lower the impeller ratio below 1.00. The calculator then adjusts flow, head, and power with affinity-law style scaling for comparison.
- 6. Does it replace manufacturer curves? No. It supports early design checks and comparative studies. Final selections should always use certified vendor curves, tolerances, and allowable operating limits.
- 7. Why might there be no operating point? The system head may exceed the pump curve across the usable range. Reducing losses or increasing speed can restore an intersection.
- 8. How accurate is the efficiency estimate? It is a modeled estimate around BEP, not a tested guarantee. Use it for planning and screening, then verify with supplier performance data.