Rotary disc filter element

In a rotary disc filter assembly for a tank having an elongate, upright shaft extending therethrough and a plurality of rotary disc filter elements arranged in vertically stacked relation on said shaft, each of said filter elements having a circular bottom plate, a hub fixed to said bottom plate at its center, a supporting mesh carried by and overlying said bottom plate, a filter mesh overlying said supporting mesh, and means clamping said meshes to said bottom plate at the periphery thereof, the improvement wherein said bottom plate is unsupported radially outwardly of its hub and is downwardly deformed to provide therein a plurality of radially extending, circumferentially spaced grooves inclined downwardly and radially inwardly, the hub of each of said filter elements having an axial length sufficiently greater than the axial depth of any of said grooves whereby, when said filter elements are in stacked relation on said shaft and the hubs of adjacent filter elements are in engagement, a radially unobstructed axial space exists between the filter mesh of each filter element and the adjacent upper filter element.