part but is instead discharged at an earlier stage it should also be noted that the mutual and relative positions and operation of the filter surface and rotor need not be as described hereinabove rather the stationary not quite uniform cylindrical part may be a member having a surface alternative in accordance with fig3 and the rotational part may be a filter surface whereby the filtrate is discharged through the rotational member the illustrated vertically oriented apparatus may also be arranged horizontally or if desired at an inclined or angled orientation a further development of the embodiment of the apparatus depicted in fig7 and 8 is shown in fig9 and 10 in which the pulp is brought axially into the apparatus through a conduit 82 a filtering chamber 83 is separated by a stationary cylinder 84 from the central portion 85 of the apparatus from which central portion the pulp may flow out through only one substantially axial slot 86 in the cylindrical inner wall 84 into the chamber 83 defined between the cylindrical surface 84 and the filter surface 87 disposed within the chamber 83 is a rotatable rotor or blade member 88 the purpose of which is to operatively keep the pulp in motion to mix it and to control the thickness of the fiber mat on the filter surface 87 the rotor or blade member 88 is preferably mounted on a shaft 89 by means of an arm 90 arranged in substantially the central portion of the apparatus and extending through a slot 91 in.