Pump Sizing and Centrifugal Pump Selection: Engineering Workflow
Engineering context
Pump sizing connects the process duty — the flow rate and head the pump must deliver — to how the pump behaves once it sits inside the real fluid network. The operating (duty) point is where the pump curve meets the system resistance curve, and that point depends on pipe losses, fittings, elevation changes, control valves, fluid properties, and downstream equipment. Selecting a pump from a duty figure alone is not enough; the same pump can land at a different duty point once the connected system, valve positions, or operating case change.
A practical workflow sizes the pump against the system it will actually operate in, comparing candidate pumps so the chosen pump runs efficiently at the desired duty point, stays within mechanical limits at alternative conditions, and keeps NPSH available above NPSH required with an acceptable margin.
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Free TrainingEngineering workflow
- Define the process duty — the required flow rate and the head or pressure rise the pump must deliver, across the relevant operating cases.
- Lay out and connect the network — place and define the boundary conditions (the fluid is selected from the database, which carries its properties, and applied at the boundary), then add the pump, valves, and equipment and connect them with pipes to establish topology.
- Assign pipe and component data — internal diameters, lengths, elevations, roughness, fittings, and equipment settings.
- Set up the operating case from the combined settings of the relevant components — boundary values together with valve positions and equipment states — not the boundary alone.
- Size the pump against the system requirement — establish the duty flow and head the pump must meet across the operating cases. This required duty defines the pump size used to shortlist candidate pumps.
- Using the identified pump size, add a candidate pump and its manufacturer curve, then solve the network to find the duty point where the pump curve meets the system resistance curve.
- Analyse NPSH available on the suction side from the system — suction pressure, fluid vapour pressure, static head, and suction losses (NPSHA is a system property, independent of the pump).
- Compare options — evaluate candidate pumps and confirm the chosen pump duty point sits in an acceptable region of its curve and that NPSHA exceeds NPSHr with adequate margin.
Why the full system matters
The same pump placed in different systems, or operated under different valve positions or boundary conditions, will produce a different duty point. NPSH available is a system property — it depends on the suction arrangement, pipe losses, and fluid vapour pressure — not a pump property. Evaluating pump performance in isolation from the connected system produces a duty point that does not reflect how the pump will actually run.
How FluidFlow helps
FluidFlow helps engineers size and review pumps inside a steady-state pipe network, including the relationship between pump performance, system resistance, flow distribution, NPSH, and equipment losses. Manufacturer pump curves and performance data can be modelled in the connected system, so the duty point and suction conditions are evaluated against the real network rather than a standalone curve.
