Abstract: A pleated filter cartridge for filtering liquids including an annular filter element having a filter material which is a thin non-perforated non-woven material of flash-spun plexifilamentary high-density polyethylene fibrils, the filter material having a pressure drop of less than 4 psid at a flow rate of 10 gal/hr and a filtration efficiency of at least 98% of 1–2 micron particulates at a pressure differential of 30 psid. The filter material preferably has a mean flow pore size greater than 4 microns while its normal pore-size filtration rating is 1 micron, and preferably has a thickness of less than about 0.15 mm, most preferably less than or equal to about 0.13 mm. The filter element preferably has two layers, including a mesh layer, preferably of a low-density polyethylene.

Abstract: Improved liquid filter apparatus of the filter-sock type is disclosed. The filter sock is a non-perforated non-woven filter material of flash-spun plexifilamentary polyolefin (preferably polyethylene) fibrils, wherein the filter material has a pressure drop of less than 4 psid at a flow rate of 10 gal/hr and a filtration efficiency of at least 98% of 1-2 micron particulates at a pressure differential of 30 psid. In certain preferred embodiments, the filter material, which is most preferably a sole sock layer, has: a pressure drop less than 1.5 psid at a flow rate of 10 gal/hr and filtration efficiency is at least 99% of 1-2 micron particulates at a pressure differential of 30 psid; a mean flow pore size greater than 4 microns while its nominal pore-size filtration rating is 1 micron; a Gurley Hill porosity rating no more than 5 sec/100 cc; a thickness of less than 0.15 mm; and/or a basis weight of less than 45 g/m2.