Method for controlling of a pump unit and a pump unit for pumping liquid or suspension

A method for controlling a pump unit for pumping liquid or suspension, the pump unit comprising a centrifugal pump and an inducer in a proximity upstream of an inlet (210) of the centrifugal pump,

• the centrifugal pump comprising a pump housing forming a flow channel inside the pump housing and an impeller configured to be rotated in the flow channel around a central axis by a shaft,
• the inducer comprising an inducer rotor having a sleeve-shaped rotor body, the inducer rotor is configured to be rotated around the central axis in the flow channel, the rotor body including a number of blades extending inwards from the rotor body,
• the inducer rotor being is separate to the impeller and a rotation speed of the inducer rotor is independently controlled in relation to a rotation speed of the impeller, the inducer comprising an electric motor that is an annular motor encircling and connected to the inducer rotor, the method comprising:
• controlling of the pump unit based on a determination of a combination of the inducer and the centrifugal pump at least on parameters of a total volumetric flow rate and pressure difference over the pump unit, and controlling the pump unit based on a rheology of a fluid to be pumped so that necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or an output power of the inducer rotor is controlled to a desired volumetric flow rate.