The present invention relates to a centrifugal pump for pumping of liquids containing pollutions mainly in the form of solid particles, which pump comprises a drive unit, a hydraulic unit, whereby the hydraulic unit comprises a pump housing (20) and a pump impeller (12) rotationally arranged inside the housing, the pump impeller comprising an upper (14) and a lower (16) cover disc and a number of intermediate vanes (18). The invention is characterised in that a bottom wall (22) of the pump housing, having a central inlet opening (24), is arranged with at least one spirally extending back flow affecting means (32, 34) on the side facing the lower cover disc extending parts of or full turns around the inlet opening.