pressure drop corresponds with a higher resistance to airflow. Pressure drop is calculated by determining the difference in total pressure at two points, typically the inlet and outlet. Filter drag is the resistance across the fabric-dust layer. The air-to-cloth ratio (ft/min or cm/s) is defined as the amount of gas entering the baghouse divided by the surface area of the filter cloth. Filter media Fabric filter bags are oval or round tubes, typically long and in diameter, made of woven or felted material. Nonwoven materials are either felted or membrane. Nonwoven materials are attached to a woven backing (scrim). Felted filters contain randomly placed fibers supported by a woven backing material (scrim). In a membrane filter, a thin, porous membrane is bound to the scrim. High energy cleaning techniques such as pulse jet require felted fabrics. Woven filters have a definite repeated pattern. Low energy cleaning methods such as shaking or reverse air allow for woven filters. Various weaving patterns such as plain weave, twill weave, or sateen weave, increase or decrease the amount of space between individual fibers. The size of the space affects the strength and permeability of the fabric. A tighter weave corresponds with low permeability and, therefore, more efficient capture of fine particles. Reverse air bags have anti-collapse rings sewn into them to prevent pancaking when cleaning energy is applied. Pulse jet filter bags are supported by a metal cage, which keeps the fabric taut. To lengthen the life of filter bags, a thin layer of PTFE (teflon) membrane may be adhered to the filtering side of the fabric, keeping dust particles from becoming embedded in the filter media fibers. Some baghouses use pleated cartridge filters, similar to what is found in home air filtration systems. This allows much greater surface area for higher flow at the cost of additional complexity in manufacture and cleaning. See also Dust collector Electrostatic precipitator References External links Baghouse Dust Collector Information Baghouse Technical Drawings Baghouse Knowledgebase Baghouse / Fabric Filter Glossary of Terms Guide To Choosing The Correct Baghouse Filter Pollution control technologies Filters