The most common type of pump installed in the world, centrifugal pumps can be purchased to perform a wide variety of functions. Construction materials can be chosen to be compatible with the process fluid. Choices include cast iron, stainless steel and various high strength polymers. This type of pump is ideal where flow rate or pressure is variable. They can be connected in series to increase flow rate, during periods of high flow, or in parallel to increase pressure. Consisting of a chamber (volute casing) and a rotating impeller, this type of pump uses the centrifugal force generated by the impeller to pump liquids.