Distinguish between positive displacement pumps and dynamic (centrifugal) pumps in terms of operation and typical applications.

• A. Positive displacement pumps move a fixed volume per cycle, capable of high pressure at low flow; centrifugal pumps impart velocity to fluid and deliver high flow with lower pressure.
• B. Positive displacement pumps always produce higher flow than centrifugal.
• C. Centrifugal pumps deliver high pressure at small volumes.
• D. Both operate identically.

Answer: (A)

The main idea is how flow and pressure relate to pump design. Positive displacement pumps trap a fixed amount of fluid and push it out per cycle, so at a given speed the output is nearly constant. This lets them build high pressure even when the delivered flow is small, and they’re especially good for precise metering and pumping viscous or high-viscosity fluids. In other words, they deliver high pressure at low flow and are well suited for jobs that require accurate dosing or high-pressure transfer of chunky liquids.

Centrifugal (dynamic) pumps work by accelerating fluid with an impeller and letting the diffuser or volute convert that kinetic energy into pressure. Their flow capability scales with how much head they’re asked to push against, so they provide large flow at moderate to low heads and generally lower pressures at a given speed. They’re ideal for moving large volumes of clean or low-viscosity liquids, such as water or coolant, where high flow is the priority and high pressure is not required.

This is why the correct statement describes positive displacement pumps as delivering high pressure at low flow, while centrifugal pumps deliver high flow with lower pressure.