This invention is a filtration structure characterized by radial fluid flow through the wall of a cylindrical configuration that is established by a stack of serrated annular wafers which are constrained for slight axial movement with respect to each other, for the establishment of two conditions. In one condition, the wafers are axially compressed into snug contact under spring bias to establish a labyrinth of radial passages for fluid flow at a selected pressure. In the other condition, the axial compression of the disks is relieved and the disks are slightly separated by back flushing under an elevated pressure in such a way that cleansing is freely effected by reverse fluid flow.