Which of the following are types of positive displacement pumps?

Positive displacement pumps are designed to move fluid by trapping a fixed amount of it and then forcing that trapped volume into the discharge pipeline. This characteristic is key to their function, especially in applications where precise volume control is important.

The types of positive displacement pumps include peristaltic, rotary, and reciprocating pumps. Peristaltic pumps move fluid by compressing and relaxing a hose or tube, creating a vacuum that draws liquid in. Rotary pumps use rotating mechanisms, such as gears or lobes, to move the liquid. Reciprocating pumps use a back-and-forth motion, usually with a piston or diaphragm, to push fluid. Each of these types provides a reliable method for handling various types of fluids, including those that are viscous or contain solids.

While the other options include some types of pumps, they may also mix in some that do not qualify as positive displacement pumps, such as centrifugal pumps, which operate on a different principle entirely by using rotational energy to impart velocity to the fluid. This fundamental difference makes the correct choice affirm the distinction among various pump types, especially in the context of fluid dynamics and wastewater treatment processes.