US Patent 11173429 Filtration device

A filtration apparatus includes a filtration tank; a layer of filtration media that filters supplied raw water by passing the raw water therethrough within the interior of the filtration tank; and a screw cleansing mechanism having a cylindrical outer cylinder which is provided within the filtration tank in a vertical orientation, a spiral shaped screw which is provided such that the long axis thereof extends in the longitudinal direction of the outer cylinder, and a screw driving member for rotating the screw, that scrubs and cleans filtration media by rotating the screw. The screw is in the shape of a coil spring.