Which of the following is not considered a rotary pump?

A roller pump is not classified as a rotary pump because it operates on a different principle. While rotary pumps function by rotating a component to create flow, a roller pump generates flow through the mechanical action of rollers compressing a flexible tube. This mechanism creates a peristaltic action, where the movement of the rollers effectively pushes fluid through the tubing.

On the other hand, centrifugal pumps, axial pumps, and diagonal pumps all operate using rotational motion. Centrifugal pumps utilize an impeller to impart kinetic energy to the fluid, moving it outward from the center, while axial and diagonal pumps involve blades that push fluid parallel or at an angle to the axis of rotation, respectively. Understanding these distinctions helps clarify why the roller pump is not categorized alongside the other types as a true rotary pump.