A sedimentation separator for separating solid fractions from a mixture consisting of air, liquid and solids fractions comprises a sedimenting vessel to which an air-separating unit is connected upstream. In an intermediate vessel arranged between the air-separating unit and sedimenting vessel there is arranged a float which closes off an air duct when the level of sediment in the sedimenting vessel has reached a predetermined height. Liquid purified by sedimentation is suctioned off from the upper end of the sedimenting vessel by means of a jet pump.