upon a screen to separate long fibers and large impurities from small fibers and fine impurities application_number US 4568493 A description with reference to the drawings a pulp slurry of waste paper to be treated which has initially been cleaned from large and dense impurities such as staples and other metallic particles is pumped by a pump 1 via a conduit 2 to a spray filter 3 having a screen 4 the spray filter 3 comprises a vessel of any convenient dimensions having fixtures suitable for retaining the screen 4 the diameter of the screen openings of the screen 4 is chosen in the range of 500 to 1000 micron the spray filter also comprises one or more spray nozzles 5 positioned to receive the slurry from conduit 2 and spray the slurry in the form of jets through air in the spray filter 3 against the screen 4 so that the pulp slurry is fractionated into a rejected first aqueous fraction containing relatively long fibres and relatively large deformable impurities of strings foils and clumps of glue and an accepted second aqueous fraction containing relatively short fibres and relatively fine impurities of small particles printing ink and filler material such as ashes and clay although the filter 3 is shown as a flat screen it may take the form of a rotating disc or a plurality of rotating discs or a drum the first aqueous fraction containing long fibres is pumped by a pump 6 from the spray filter 4 to a coarse screen 7 via a conduit 8 the diameter of the screen openings of the screen 7 is chosen in the range of 0 2 to 0 3 millimeters preferably.