How does a centrifugal pump differ from a positive-displacement pump?

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The main idea is how the two pump types move fluid and how their flow responds to system pressure. A centrifugal pump relies on an impeller spinning to add velocity to the liquid. That imparted energy is then converted to flow in the discharge line, so the amount of liquid moved per unit time depends on the head (pressure) in the system. It does not deliver a fixed volume with every rotation.

A positive-displacement pump, on the other hand, traps a specific amount of fluid and pushes that exact volume out with each cycle. That means the output per cycle is essentially fixed, so the flow is predictable and largely independent of the discharge pressure (up to the pump’s limits).

So the key distinction is: centrifugal pumps use an impeller to impart velocity to the fluid, with flow that varies with system pressure, while positive-displacement pumps move a fixed volume per cycle, yielding more constant flow.