to a member 42 keyed to the shaft 36 as indicated at 44 the rotor 34 further comprises end plates 46 connecting an outer wall 48 to the hollow cylinder 40 and sealing the ends of the rotor with respect to the flow of slurry as best seen in fig2 the rotor 34 comprises a cam like configuration including a pair of blunt leading edges 50 facing in the direction of rotation 52 respectively followed by arcuate sections 54 in a particular construction the arcuate sections 54 have the same radius of curvature with the respective centers of the radii diametrically offset with respect to the axis of rotation although only two of such semicylincrical structures have been shown a plurality may be provided for very large pressure screens as used in the specification and claims hereof 34 blunt 34 when used in reference to the rotor shall mean a surface so shaped as to be capable of capturing a certain volume of stock and accelerating it up to rotor velocity thus for example the leading edges 50 could be forwardly inclined with respect to the direction of rotation or could be concave in shape referring to fig3 and 4 two different profiled surfaces are illustrated for the screen namely the profile 56 in fig3 and the profile 58 in fig4 normally the profile is only provided on the inner surface of the screen and other profiles than those shown could also be used after realizing the pulsation phenomenon set forth above investigations were undertaken to determine the cause thereof including the geometric causes the dynamic causes and.