Corrugated axial filter with simple fold pattern and method of making it

A method of making a corrugated axial filter comprising providing a continuous sheet of filter material extending along a longitudinal direction, folding said sheet into a zig-zag pattern along a plurality of parallel lateral fold lines each perpendicular to said longitudinal direction, said sheet in said zig-zag pattern having a plurality of sections extending back and forth in zig-zag manner between a front set of apexes formed by a first set of said fold lines, and a rear set of apexes formed by a second set of said fold lines, said zig-zag pattern having top and bottom edges extending in said zig-zag manner between said front and rear sets of apexes, providing a bottom wall along said bottom edges, providing a top wall along said top edges, to form a plurality of flow channels each having an upstream opening at an upstream dirty frontside and having left and right sidewalls formed by adjacent said sections of said zig-zag pattern, said left and right sidewalls extending rearwardly from respective front apexes on opposite right and left sides of said opening, said left and right sidewalls tapering towards each other as they extend rearwardly and merging at a rear apex to define a triangular shaped said flow channel, such that left and right sidewalls of adjacent flow channels are a single continuous sheet of filter material in said zig-zag pattern with a plurality of fold lines comprising said first set of fold lines at said upstream dirty frontside of said filter and a second set of fold lines at a downstream clean backside of said filter said flow channels extending axially from said upstream dirty frontside to said downstream clean backside, and comprising:

• forming the top wall of a first flow channel as the bottom wall of a second flow channel immediately above said first flow channel;
• forming the bottom wall of said first flow channel as the top wall of a third flow channel immediately below said first flow channel;
• providing a nondoubled single layer second sheet as both said top wall of said first flow channel and said bottom wall of said second flow channel, said second sheet having a top surface facing upwardly into said second flow channel, said second sheet having a bottom surface facing downwardly into said first flow channel;
• providing a nondoubled single layer third sheet as both said bottom wall of said first flow channel and said top wall of said third flow channel, said third sheet having a top surface facing upwardly into said first flow channel.