US Patent 8147693 Multi-layer filter including retainers

A multi-layer filter including a first media layer surrounded by a second media layer, a third media layer surrounding the second media layer, and at least one retainer disposed between the first and second media layers or between the second and third media layers. The first, second and third media layers surround the central axis of the filter. The filter has multiple media layers in a compact package, providing increased media surface area which allows greater contaminant holding capacity, lower pressure drop, and lower face velocity.