A dirty filter is first "pre-cleaned" by blowing air from the inside of the filter as it is rolled horizontally on rubber wheels.  Some contaminants fall into a pan while others are captured by the bag house filtration system.
The filter is then sonic dry cleaned.  The dirty filter is locked down on a turntable in a dry cleaning machine.  The door id closed and the turntable revolves at high speed.  The filter is vibrated while an air nozzle turns up and down the inside and a vacuum device moves up and down the outside.  This stage takes approximately five to ten minutes.