Abstract: The apparatus comprises a plurality of tubular classifiers connected in series to one another and into sections which are parallel connected to a manifold to form a unit of the apparatus. Each tubular classifier has pipes for tangential admission of a liquid mixture and the removal of concentrate and filtrate, and vertically extending transverse partitions are provided immediately adjacent to end plates. The partitions have through holes arranged along a spiral line. The holes receive the ends of the tubular filtering elements and said ends are secured therein and the elements are arranged at an angle to the longitudinal axis of a casing and to the partitions.