US Patent 8231337 Pump for pumping liquids including solid matter

The invention relates to a pump for pumping contaminated liquid including solid matter, comprising a pump housing provided with a rotatable impeller suspended in a drive shaft and having at least one vane, and an impeller seat, at least one part of the impeller and the impeller seat being movable in the axial direction in relation to each other. Furthermore, the impeller seat presents at least one groove in the top surface thereof.