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. After defining the process duty, engineers lay out and connect the network, placing and defining the boundary conditions, then assign pipe and component data and set up the operating case from the combined settings of the relevant components. The required duty defines the pump size used to shortlist candidates; a candidate pump and its manufacturer curve are then added and the network solved to find the duty point where the pump curve meets the system resistance curve. NPSH available is analysed from the suction side as a system property, and candidate pumps are compared so the chosen pump runs efficiently at the desired duty point, stays within mechanical limits at alternative conditions, and keeps NPSHA above NPSHr with an acceptable margin.

Engineering workflow

1. Define the process duty — the required flow rate and the head or pressure rise the pump must deliver, across the relevant operating cases.
2. 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, from where it is carried through the connected system), then add the pump, valves, and equipment and connect them with pipes to establish topology.
3. Assign pipe and component data — internal diameters, lengths, elevations, roughness, fittings, and equipment settings.
4. 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.
5. 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.
6. 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.
7. 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).
8. Compare options — evaluate candidate pumps against each other and confirm, for the chosen pump, that the duty point sits in an acceptable region of its curve (efficiency, away from minimum-flow and run-out) and that NPSHA exceeds NPSHr with adequate margin, across pump sizes, impeller trims, or operating cases.

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.

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