A rotodynamic pump is a kinetic machine in which energy is continuously imparted to the pumped fluid by means of a rotating impeller, propeller, or rotor, in contrast to a positive-displacement pump in which a fluid is moved by trapping a fixed amount of fluid and forcing the trapped volume into the pump's discharge. Examples of rotodynamic pumps include adding kinetic energy to a fluid such as by using a centrifugal pump to increase fluid velocity or pressure.

A pump is a mechanical device generally used for raising liquid from a lower level to higher one. This is achieved by creating a low pressure at the inlet and high pressure at the outlet of the pump. Due to low inlet pressure, the liquid rises from where it is to be stored or supplied. However, work has to be done by a prime mover to enable it to impart mechanical energy to the liquid which ultimately converts into pressure energy.

Considering the basic principle of operation, pumps can be classified into two categories:

Pumps are classified as follows:

A positive-displacement pump operates by forcing a fixed volume of fluid from inlet pressure section of the pump into the discharge zone of the pump. It can be classified into two types:

Positive-displacement rotary pump move the fluid by using a rotating mechanism that creates a vacuum that captures and draws in the liquid. Rotary positive-displacement pumps can be classified into two main types:

Reciprocating pumps move the fluid using one or more oscillating pistons, plungers or membranes, while valves limit fluid motion to the desired direction.

Pumps in this category are simple, with one or more cylinders. They can be either single-acting, with suction during one direction of the piston motion and discharge on the other, or double-acting, with suction and discharge in both directions.