Multi-stage air filter assembly

Claim 1

A multi-stage assembly for filtering forced air, comprising a housing divided vertically into releasably connected upper and lower parts in metal-to-metal contact, a vertical bore in said upper part and having a downward extension into said lower part, a fine filter unit in said upper part and having a sleeve slidably received in said bore therein, a coarse filter unit slidably received in said bore extension in tandem with said fine filter unit, spaced inlet and outlet air ports in said upper part, a vertically directed helical air passage in said upper part bounded laterally by a side wall thereof and said sleeve and opening upwardly onto said inlet port and downwardly onto an interior of said lower part outwardly of said bore extension, said passage directing air from said inlet port to flow cyclonically downwardly therethrough for centrifugally separating contaminants from said air and discharging said air and contaminants into said lower part, baffle means in said lower part between a side wall thereof and said coarse filter unit for interrupting the cyclonic motion of said air from said passage to prevent forming of a boundary layer of dead air along said side wall of said lower part while passing said air and contaminants, a sump in said lower part below said side wall for collecting separated contaminants and directing said air upwardly for flow in succession through said coarse and fine filter units to said outlet port, said upper and lower parts being externally finned for heat transfer to ambient air, drain tube means extending upwardly from said sump through said filter units to an upper end of said housing and releasably mounting said filter units, and drain valve means surmounting said housing and connected to an upper end of said tube means for periodically draining collected contaminants from said sump.