A sorting apparatus for sorting fiber suspensions heavily laden with rubbish and other contaminants, which sorter has two successive sorting units each having a ring-shaped strainer space, which are likewise successive, and an accepts space with a rotationally symmetric strainer between the accepts space and strainer space. The first sorting unit is pressurized above atmospheric pressure; diluting water is fed to the second unit strainer space; and a rotating plate is mounted between the first and second sorting units to control the flow between the strainer spaces.