Abstract: A cartridge filter element for installation in a plenum of a filtration housing that receives a dirty air flow and cleans that flow by flow passage through a filter material or media of the cartridge filter element, with the cleaned air then passed out of a discharge end of the cartridge filter element and vented through a clean air discharge line. The cartridge filter element includes a section of the filter material that is formed, as by rolling, into an outer cylinder and includes bands fitted therearound for maintaining its cylindrical shape. An access door, that is preferably a flat plate having four corners, is centered across the outer cylinder rear end to extend at a right angle therefrom to close off that cylinder rear end.