Filtering devices with at least one filtering cavity

Claim 1

In a filtering device, the combination comprising: at least one filtering cavity in the form of a hollow member of filter material; means defining an inlet enclosure containing said filtering cavity; means for introducing a gas to be filtered into said inlet enclosure so as to be exposed to the external sides of said filtering cavity; an outlet enclosure separated from said inlet enclosure by a separating partition; an open ended connecting pipe connecting the cavity interior to the oulet enclosure by passing through the separating partition; exhausting means for evacuating filtered gas out of said outlet enclosure, said filtered gas having passed through the cavity from the exterior thereof to the interior thereof; and gas injection means, including an injection nozzle, arranged in said outlet enclosure opposite the open end of the connecting pipe in the outlet enclosure for introducing from time to time and during relatively short periods a flow of clearing gas under pressure into said filtering cavity, in counter flow with respect to the normal issuing flow of the filtered gas out of the cavity; and means connecting said injection means to a supply of compressed clearing gas, through controllable valve means; said connecting pipe being internally provided with fixed helicoid blade means for effecting rotation of the flow of clearing gas delivered by said injection means as said clearing gas passes into said filtering cavity.