The fabric filter unit consists of one or more isolated compartments containing rows of fabric bags, in the form of round, flat, or profiled tubes, or pleated cartridges. The dust carried by the air mass passes, by suction or depression, along the area of the bags and then radially through the fabric, with the outer part of the bags retaining the dust particles. The filtered air, once inside the bags, passes to the upper clean air chamber (plenum) through the venturi nozzles and from there to the outside by means of the extractor (fan). The filter operates cyclically, alternating relatively long filtering periods with short cleaning periods. During cleaning, the dust accumulated on the fabric bags is removed. Fabric filters collect particles ranging in size from submicrometers to several hundred microns in diameter with efficiencies generally greater than 99 or 99.9 percent. The layer of dust, or dust cake, accumulated on the fabric is mainly responsible for this high efficiency. The cake is a barrier with tortuous pores that trap particles.