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SESK: Stuff Everyone Should Know · sesk.info/eng-positive-displacement-flow

What chiefly sets an ideal positive-displacement pump's flow rate?

It is set by displacement per cycle times speed.

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  1. Outlet pressure alone
  2. Diffuser angle
  3. Displacement per cycle and speed ✔

Why: A positive-displacement pump moves a nearly fixed volume each stroke or revolution. Its flow therefore follows cycling speed, while system resistance mainly determines pressure.

Huh, didn't know that: Because a blocked outlet can rapidly raise pressure, these systems commonly need relief protection.

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The displacement pump always delivers because it works by volume.
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References

Answer: Displacement per cycle and speed. A positive-displacement pump moves a nearly fixed volume each stroke or revolution. Its flow therefore follows cycling speed, while system resistance mainly determines pressure.

  1. US Department of Energy, Improving Pumping System Performance www1.eere.energy.gov/manufacturing/tech_assistance/pdfs/pump.pdf
    positive displacement pumps have a fixed displacement volume. Consequently, the flow rates they generate are directly proportional to their speed.
    Checked 2026-10-10.

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