Abstract: A method and device for unclogging filter cloths for use in filter apparatus particularly apparatus of the kind wherein the cloth describes a closed loop between a filtering station and an unclogging station.Gas is ejected from one or more nozzles through the cloth which is vibrated at a sonic and/or ultrasonic frequency at a location opposite the nozzle ejection head. The cloth is simultaneously stretched at the same location into a projecting shape having leading and trailing edges with a length, in the direction of motion of the cloth, of not more than three times their height in the direction perpendicular to the direction of motion of the cloth.