The AAF Amer-Therm employs woven fabric, tubular filter bags, open to the hoppers at the bottom and sealed to metal caps at the top. Contaminated gas enters the baghouse inlet manifold and is distributed to each hopper, from which it enters the filter bags through collars in the tube sheets (hopper tops) to which individual bags are clamped. Particulate contaminants are deposited on the inner surface of the bags as the gases pass through the media and are discharged into the atmosphere. The cleaning of bags is accomplished by brief reversal of gas flow through one section of the bags at a time, causing the dislodged filter cake to drop into the hopper below. Air reversal is accomplished by dampening off the compartment being cleaned and opening another damper, which leads to a separate duct system connected to an auxiliary reverse air fan. The operation is repeated in turn until all compartments have been cleaned and returned to service.
Pressure operation is usually selected. Here, the main fan is on the inlet side (upstream) of the baghouse, requiring only that the portions of the collector in contact with contaminated gases be sealed gas-tight. The "clean side" housing may be merely weather tight. Although not usual, suction operation could be selected. Here, gas-tight construction and bracing the housing for high internal negative pressures is necessary.