Patent ID: 6391200
Filing Date: 2002-05-21
Classification: B01D

Abstract:
A spiral wound filter element comprising:alternating layers of filter medium and diffusion medium wrapped about a cylindrical core defining a central axis of the filter element, the alternating layers extending from a radially innermost layer of the filter element to a radially outmost layer of the filter element, the diffusion medium defined by a continuous lengthwise sheet of mesh material, the filter medium defined by at least one sheet of filter material arranged along the length of the continuous sheet of mesh material, the alternating layers of filter medium and diffusion medium defining three distinct radially disposed layered filtering sections surrounding the cylindrical core, including a fist filtering section having radially outer prequalifying layers, a second filtering section having middle prequalifying layers and a third filtering section having radially inner qualifying layers, the radially outer prequalifying layers and the middle prequalifying layers defining about two-thirds of the radial distance from the radially outermost layer of the filter element to the radially innermost layer of the filter element, wherein: a) the filter material within the radially outer prequalifying layers includes a number of perforations forming radially extending by-pass apertures; b) the filter material within the middle prequalifying layers includes a fewer number of perforations forming radially extending by-pass apertures than a perforated sheet of the radially outer prequalifying layers; and c) the first material within the radially inner qualifying layers is imperforate.