Pumps are used widely and account for a significant portion of global electricity usage. There are two main types of pumps - positive displacement pumps which move a fixed volume of fluid with each cycle, and dynamic pumps such as centrifugal pumps which use a rotating impeller to increase fluid pressure or velocity. Centrifugal pumps make up the majority of pumps installed and work by using an impeller to impart kinetic energy to fluid and a volute casing to convert this to pressure. Key components include the impeller, shaft, and casing which houses and supports the rotating components. Understanding pump types and operations is important for assessing their energy efficiency opportunities.