Helical wrapped filter element

An element for treating a fluid flowing through the element, which fluid treatment element comprises at least one filter medium sheet comprising a fibrous mass of nonwoven microfibers capable of removing particulates from a fluid helically wrapped around a pervious, hollow tube and at least one diffusion layer which allows for lateral flow of said fluid within said fluid treatment element, wherein said diffusion layer is a spun-bonded polypropylene nonwoven sheet material having a weight of between about 20 g/m.sup.2 and about 60 g/m.sup.2.

An element for treating a fluid flowing through the element, which fluid treatment element comprises at least six filter medium sheets helically wrapped around a pervious, hollow, cylindrical tube to form an overlap of 50% of the width of each of said filter medium sheets, wherein each of said filter medium sheets comprises a fibrous mass of nonwoven polypropylene fibers secured to a diffusion layer comprising a porous polypropylene substrate, the innermost of said filter medium sheets is positioned such that said diffusion layer associated therewith is oriented inwardly toward said cylindrical core, the other filter medium sheets are positioned such that said diffusion layers associated therewith are oriented outwardly away from said cylindrical core, and at least three of said filter medium sheets have different pore ratings and are positioned such that said filter medium sheet pore ratings decrease in the normal direction of fluid flow through said fluid treatment element.