cylindrical screen unit and through which feed material passes downwardly as shown in fig4 each circular plate 22 has a plurality of openings 22 a at the periphery thereof through which feed material passes downwardly separator unit 16 further includes a plurality of conical members 24 shown in fig5 each extending from the inner periphery of an upper circular plate 22 downwardly and radially outwardly to the next lower circular plate 22 each circular plate 22 has a second plurality of openings 22 b radially inward of a circle at which a conical member 24 meets a circular plate a particle size classifier constructed in accordance with the present invention further includes a vertically disposed center pipe 26 extending through the plurality of circular plates 22 and to which the plurality of circular plates are fixed the upper end of center pipe 26 preferably is connected to funnel 14 of the feed material supply means outside housing 10 center pipe 26 has at an upper end means for conducting feed material from funnel 14 of the feed material supply means to the center pipe and from within the center pipe to within cylindrical screen unit 18 for the embodiment of the invention being described center pipe 26 is hollow throughout the length thereof and feed material is conducted at the upper end of the center pipe through first and second diametrically opposed openings 28 only one being shown in fig1 and 2 in the center pipe at a point within cylindrical screen unit 18 to the cylindrical screen unit a blank 30 in center pipe 26 below first and second openings 28 blocks downward movement of feed material in the center pipe the lower end of center pipe 26 preferably.