Patent ID: 7344580

Claim:
A filter unit for filtering polluted air, said filter unit comprising a housing having an upper end and a lower end; said housing having an inlet located at said lower end and an outlet located at said upper end; a plurality of part-filter units located in said housing, wherein said part-filter units are arranged one above the other; wherein each of said part-filter units comprises a plurality of filter mats located parallel with each other and with the direction of flow of the polluted air; wherein the direction of flow of a volume of air in the housing is from said lower end to said upper end of said housing; wherein all of the volume of air entering the inlet is filtered by a first part-filter unit located at the lowermost part of the housing, and then successively by part-filter units located above the first part-filter unit; and wherein matter trapped by said part-filter units drops by gravitational force to said lower end of said housing.