Abstract: In screening apparatus for paper fiber stock of the type wherein a cylindrical perforate screen member defines screening and accepts chambers on the inner and outer sides thereof in a closed, pressurized housing, the inlet chamber for stock to be screened is located below the screening chamber to facilitate elimination of high specific gravity reject materials before the stock reaches the screening chamber. Special provision is made for accelerating the flow of plastic and other reject materials of lower specific gravity than wet paper fibers to a reject chamber above the screening chamber, and special provision is also made for preventing recirculation of such reject materials to the lower end of the screening chamber and thereby concentrating them in the reject chamber from which they are removed by way of a dewatering device that delivers essentially dry reject material for ready disposal while preventing the escape of pressure from the housing.