distance u201c 6 u201d of between 0 4 mm and 0 6 mm from imaginary cylindrical surface s 1 this distance being referred to as the profile height each generally circumferentially extending facet 44 has a thickness u201c t u201d of between about 2 3 and 2 5 mm and is inclined toward the upstream at an angle u201c u03b1 u201d of between about 76 u00b0 and 80 u00b0 its respective diametrally extending centerline slit 52 having a width u201c w u201d of between about 0 11 mm and 0 145 mm is defined between upstream generally diametrally extending facet 46 of each vane 32 and downstream generally diametrally extending facet 42 of the next vane upstream therefrom together the downstream generally diametrally extending facet 42 trailing edge 50 generally circumferentially extending facet 44 and upstream generally diametrally extending facet 46 collectively define the supply contacting surface 54 of screen basket 30 fig3 illustrates foil 56 having leading edge 58 and trailing edge 60 defined thereupon as leading edge 58 of foil 56 passes over each slit 52 it is theorized that it introduces a negative pressure upon the slit it is passing over tending to clear the slit of stickies and other debris that may be deposited there while the positive pressure.