A mechanical device used to transport a fluid from one place or level to another by imparting energy to the fluid. The three broad groupings are reciprocating, rotary, and (p. 305) centrifugal-type pumps. The most commonly used pump is the centrifugal type, which has a rotating impeller used to increase the velocity of the fluid and where part of the energy is converted to pressure energy. Rotary and reciprocating pumps are positive displacement pumps in which portions of fluid are moved in the pump between the teeth of gears, and by the action of a piston in a cylinder, respectively. There are many variations of these types and each has a particular application and suitability for a fluid in terms of its properties, required flow rate, and delivery pressure. Pumps that do not conform to these groupings include acid eggs, air-lift pumps, and steam ejectors. All involve the use of energy to transport the fluid.