How do positive-displacement pumps differ from kinetic pumps?

Pumps are primarily classified by how they impart energy to a fluid. The fundamental differences between positive-displacement and kinetic pumps are as follows:1

• Mechanism of Action: Positive-displacement pumps lift and move a fixed volume of fluid with each cycle of a piston or rotor, literally pushing or displacing the fluid from the casing. In contrast, kinetic pumps impart velocity to the fluid using a rapidly rotating impeller, converting that velocity head into pressure head.2341
• Performance and Pressure: The flow capacity of a positive-displacement pump is generally unaffected by the system pressure, whereas the flow rate of a kinetic pump depends on the operating pressure—higher pressure typically results in lower discharge. Broadly, positive-displacement pumps are suited for moving lower volumes at high pressure, while kinetic pumps are designed to move high volumes at lower pressure.31
• Fluid Characteristics: Kinetic pumps, such as centrifugal pumps, operate best with relatively nonviscous liquids and can suffer from reduced capacity with viscous fluids. Many positive-displacement designs, such as screw pumps, are capable of handling very viscous liquids.42