Retrofitting and use of rectangular filters, assembly and method for filtration

A filter assembly for filtering liquids, comprising:

• a) a filter housing;
• b) a dirty fluid inlet to said filter housing;
• c) a clean liquid outlet from said filter housing beneath a separation plate for separating dirty fluid from clean fluid;
• d) said separation plate located inside said filter housing between said dirty fluid inlet and said clean liquid outlet, said separation plate having at least one opening in communication with said clean fluid outlet;
• e) an adaptor plate secured to an inner circumference of said filter housing between said dirty fluid inlet and said separation plate, wherein said adaptor plate has a plurality of openings and a plurality of perforated supports mounted thereon corresponding to each of said openings, and wherein at least one spacer is provided between said separation plate and said adaptor plate;
• f) a plurality of rectangular shaped filters of pleated filter media enclosed in said filter housing mounted on said adaptor plate towards said dirty fluid inlet, wherein each of said rectangular shaped filters has a central void surrounded by an inner surface of said pleated filter media, a solid first end cap, a second end cap having an opening located therein to communicate with said central void in said pleated filter media, wherein each said central void extends from said solid first end cap to said second end cap, and each said rectangular shaped filter individually surrounds each of said plurality of perforated supports extending from said adaptor plate;
• g) each said second end cap of each said rectangular shaped filter is removably mounted on said adaptor plate with a sealing member that avoids liquid bypass, wherein said adaptor plate has openings corresponding to said openings in said second end caps, such that a dirty liquid to be filtered passes from an external surface of said pleated filter media into said central void of said rectangular shaped filters and thereby becomes filtered clean liquid, and said filtered clean liquid passes through said openings on said second end caps into said corresponding openings in said adaptor plate;
• and
• h) a chamber provided in said filter housing below said separation plate to collect said filtered clean liquid before said filtered clean liquid exits said clean liquid outlet.