Positive-Displacement Pumps: Modeling Fixed Flow and Discharge Pressure

Engineering context

A PD pump delivers an essentially fixed volumetric flow per revolution, largely independent of discharge pressure. The system resistance does not set the flow: it sets the pressure the pump must develop to push that fixed flow through the route.

Booster pumps add head in series with an existing driver to reach a higher operating pressure or recover head lost along a long route.

Engineering workflow

1. Decide: fixed-displacement source (PD pump) or curve-following machine in series (centrifugal booster).
2. For a PD pump, pick the component that matches your data: Positive Displacement Pump or Compressor when sizing off vendor performance-factor data (covers most piston, diaphragm, gear, and lobe pumps); Rotating Positive Displacement Pump only when you have slip-capacity-vs-viscosity data (e.g., screw pumps).
3. Lay out the route and assign pipe, fitting, and fluid data.
4. For a booster, add a second pump component in series and define its performance curve.
5. Set boundary conditions at supply and delivery ends.
6. Solve and read developed pressure, velocities, and power (PD) or combined operating point (booster).
7. Check discharge pressure against equipment and pipe ratings.

How FluidFlow helps

Positive Displacement Pump or Compressor and Rotating Positive Displacement Pump components both represent the fixed-flow machine — pick the one matching your available vendor data. Route resistance and fluid properties solve together, so you see developed pressure and power directly.

See how FluidFlow’s Pump Modeling module handles this.

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