Patent ID: 7766605

Claim:
A centrifugal pump for pumping liquids containing pollutions mainly in the form of solid particles, said pump comprising: a drive unit, and a hydraulic unit, wherein 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 pump housing comprising a bottom wall ( 22 ) facing the lower cover disc and having a central inlet opening ( 24 ), wherein a circular gap ( 30 ) separates a space 29 arranged between the lower disc ( 16 ) and the bottom wall ( 22 ) from said central inlet opening ( 24 ), wherein the bottom wall ( 22 ) of the pump housing is arranged with at least one spirally swept, back flow affecting means ( 32 , 34 ) on the side facing the lower cover disc ( 16 ) extending parts of or full turns around the inlet opening, and portions of said back flow affecting means ( 32 , 34 ) and an upper surface of the bottom wall ( 22 ) being located adjacent the circular gap ( 30 ) are arranged below said circular gap ( 30 ).