A machine for moving fluid by accelerating it radially outward. More fluid is moved by centrifugal pumps than by all other types combined. The smooth, essentially pulsationless flow from centrifugal pumps, their adaptability to large capacities, easy control, and low cost make them preferable for most purposes. Exceptions are those in which a relatively high pressure is required at a small capacity, or in which the viscosity of the fluid is too great for reasonable efficiency.