Rotating diffuser pump

A centrifugal pump with a rotating impeller and a rotating diffuser. The diffuser may be rotated with a controlled speed to broaden the operational range of the pump. Such control may be done independently of the rotational speed of the impeller to tailor pump operation to a particular NPSH, efficiency, fluid flow or related requirement. In one preferred form, the impeller and diffuser are made to counter-rotate relative to one another, while the independent rotational speed of each may be provided by one or more motors, as well as a variable-speed transmission coupled to such motor or motors. Such a pump is optimized for specific speed operating ranges beneath those associated with axial flow pump configurations.