Abstract: A backwashable filter includes a generally cylindrical housing, an inlet opening into the housing and an outlet opening from the housing, a cylindrical filter basket within the housing and arranged between the inlet and the outlet openings, and a backwashing arm bearing against the inside of the filter basket and being rotatable around the inside face of the filter basket. The filter basket comprises a perforated core a filter medium wrapped around the perforated core and a perforated flexible outer clamping band wrapped around the outside of the filter medium with tensioning means to apply tension to the clamping band to clamp the filter medium tightly against the perforated core. This clamping band constrains the filter medium and so prevents it flexing with rotation of the backwashing arm and this enhances its life.

Abstract: A backwashable filter comprises a generally cylindrical housing with an inlet and an outlet, a cylindrical filter basket located within the housing between the inlet and the outlet, and a backwashing arm bearing against the inside face of the filter basket and arranged to rotate about the axis of the filter basket. The filter basket is formed by an inner and outer perforated cage with a filter medium interposed between them. The outer surface of the inner cage is configured to provide channelling between the inner cage and the filter medium to allow liquid to be filtered to contact substantially all of the inner surface of the filter medium. Direct flow of liquid to be filtered from the inside of the inner cage into the backwashing arm along the channelling is prevented by arranging the channelling axially or by arranging the channelling in the circumferential direction and then providing a wide shoe on the backwashing arm.