A low maintenance filter, series FN1 eliminates the need for element replacement. SMC's unique element construction is composed of a series of grooved filter plates and wave washers placed one above the other. When compressed, the gaps between the filter plates and wave washers filter foreign matter. When decompressed, the element widens the gap between the filter plates and wave washers, allowing dust and foreign particles caught between the plates to be washed away. The gaps between the filter plates are equally maintained by the wave washers to allow stable back-flush operation.