What are the two general categories of pumps?

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Pumps are grouped into two broad categories: positive displacement pumps and dynamic (centrifugal) pumps. A positive displacement pump traps a specific amount of fluid and then moves it through the system, so the output is essentially fixed per cycle. This makes them ideal when you need precise dosing or to push fluids at higher pressures, even if the system resistance changes. Dynamic or centrifugal pumps use an impeller to fling fluid outward, creating flow by converting speed into head. Their output depends on the system back pressure: they deliver large volumes at lower pressures, and the flow decreases as back pressure rises. They’re commonly used for moving large quantities of water with moderate pressure. The other options describe specific pump types or installation methods, not the fundamental categories.