High volume self-cleaning filter

A filter unit comprising:

• a housing having a longitudinal axis, an inlet for liquid carrying solid contaminants, an outlet for filtered liquid, and a back-flush inlet and a back-flush outlet for cleansing fluid, said housing containing
• a substantially cylindrical filter element having a longitudinal axis parallel to the longitudinal axis of said housing, and
• a conduit disposed in the filter element, said conduit having a longitudinal axis coincident with the longitudinal axis of said filter element and being in fluid communication with said back flush outlet for cleansing fluid;
• cleansing members disposed along said conduit, each of said cleansing members extending from said conduit to said filter element and having an aperture to allow the flow of cleansing fluid into said conduit;
• means for detecting the degree of contamination of said filter element;
• means for closing said inlet and said outlet for liquid and opening said back-flush inlet and said back-flush outlet for cleansing fluid when said degree of contamination reaches a level at which flow of liquid through said filter element falls below a predetermined level;
• and
• means for rotating one or both of said conduit and said filter element about its longitudinal axis;
• wherein said inlet and said outlet for liquid are arranged such that said liquid carrying solid contaminants flows into an interior of said cylindrical filter element, said filter element filters the solid contaminants from the liquid, and the filtered liquid passes through said cylindrical filter element to an exterior thereof before exiting said filter unit via said outlet for filtered liquid, and
• wherein said back-flush inlet and back-flush outlet for cleansing fluid are disposed such that said cleansing fluid flows into a space defined between the filter element and the housing and flows through said filter element from the exterior thereof in a direction opposite the flow of said filtered liquid before exiting said filter unit via said cleansing members, said conduit, and said back-flush outlet while said rotating means rotates at least one of said conduit and said filter element.