Density gradient filtration media

摘要

A filtration unit comprising a filtration media subunit secured in an outer frame. The subunit comprises a fibrous filtration media enclosed in an inner frame having an upstream frame element and a downstream frame element. Each frame element has longitudinal and transverse struts and the intersection of these struts is in a single plane on the side of the frame elements which contact the filtration media. In one embodiment the filtration unit is enclosed in a sock of knit fabric; in another embodiment, there is a piece of knit fabric between the outer frame and the downstream frame element of the inner frame. The longitudinal struts may have portions which are perpendicular to and project beyond the principal plane of the periphery of the downstream frame element. If such perpendicularly projecting portions are provided, they are preferably arcuate in configuration.