Pump Curve Comparison

Inputs

Enter the flow and head points for each pump in a separate box. Points must refer to the same speed and impeller diameter. The optional third column is pump efficiency. Separate columns with spaces or tabs. Decimal points and commas are accepted. Opening values are illustrative and do not describe a product.

Calculation

The system curve combines static head and a loss proportional to the square of flow. The tool interpolates linearly between pump points and never extrapolates. Rising curves are rejected and each pump reports its own errors. In the example both curves meet at 36 m³/h and 20 m. At a density of 1000 kg/m³ and 80 percent efficiency the shaft power is about 2.452 kW.

Energy and limits

Specific energy is shaft power divided by volume flow. Annual electrical energy also needs motor efficiency and operating hours. Cost requires an energy unit price. Missing efficiency prevents an energy estimate. Include drive losses in the motor efficiency input. Cavitation, motor sizing, manufacturer tolerances and permissible operation are outside this preliminary calculation. The annual estimate assumes a constant operating point.

Compare efficiency at the same operating point

Give two example pumps the same head points: 20 m at zero flow, 10 m at 18 m³/h and zero head at 36 m³/h. Choose static system head 5 m and loss 5 m at reference flow 18 m³/h. Both curves intersect the system at head 10 m. Enter 50 in the efficiency column on all three rows of the first pump and 80 on all three rows of the second. If only the operating point row contains efficiency, shaft power cannot be calculated. These constant efficiencies are fictional. With example density 1000 kg/m³, shaft powers are approximately 0.980665 and 0.612916 kW. These curves are fictional.

Equal flow and head do not imply equal power. Comparing power alone at different operating points does not compare equal service either. First establish required flow and the conditions represented by the curves.

The efficiency column is pump efficiency, while motor efficiency is a separate input. Entering a fraction instead of a percentage corrupts the energy result. Annual energy assumes the selected operating point persists for the entered hours. Treat periods at different flows separately. This preliminary calculation does not establish cavitation performance, operating range or mechanical suitability of the lowest power option.