Machine for moving liquids and gases. Its two major parts are the impeller (a wheel with vanes) and the circular pump casing around it. In the most common type, called the volute centrifugal pump, fluid enters the pump at high speed near the centre of the rotating impeller and is thrown against the casing by the vanes. The centrifugal pressure forces the fluid through an opening in the casing; this outlet widens progressively in a spiral fashion, which reduces the speed of the fluid and thereby increases pressure. Centrifugal pumps are used for many purposes, such as pumping liquids for water supply, irrigation, and sewage disposal systems. They are also used as gas compressors.
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A water or mud-lifting machine that, according to the Brazilian historian of science Reti, "must be characterized as the prototype of the centrifugal pump" appeared as early as 1475 in a treatise by the Italian Renaissance engineer Francesco di Giorgio Martini. True centrifugal pumps were not developed until the late 1600's, when Denis Papin made one with straight vanes. The curved vane was introduced by British inventor John Appold in 1851.
A centrifugal pump works by the conversion of the rotational kinetic energy, typically from an electric motor or turbine, to an increased static fluid pressure. This action is described by Bernoulli's principle. The rotation of the pump impeller imparts kinetic energy to the fluid as it is drawn in from the impeller eye (centre) and is forced outward through the impeller vanes to the periphery. As the fluid exits the impeller, the fluid kinetic energy (velocity) is then converted to (static) pressure due to the change in area the fluid experiences in the volute section. Typically the volute shape of the pump casing (increasing in volume), or the diffuser vanes (which serve to slow the fluid, converting to kinetic energy in to flow work) are responsible for the energy conversion. The energy conversion results in an increased pressure on the downstream side of the pump, causing flow.
A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts. A multistage centrifugal pump has the following two important functions:
If a high head is to be developed then the impellers are mounted on same shaft (series) while for large quantity of discharge of liquid, the impellers are mounted on different shafts (parallel).