GLOSSARY OF TERMS

Abrasion Resistance: The ability of a fiber or fabric (media) to withstand surface wear.

ACFM:  Actual cubic feet of gas per minute – Total volume of gas flowing per minute at the operating temperature, pressure, elevation and composition.

Air-to-Cloth Ratio: The ratio between ACFM flowing through a dust collector and the square feet of filter area available (ACFM/Ft²).  Sometimes this is referred to as the velocity of air through the cloth.

Baghouse: An air filtration devise utilizing fabric filter bags for removing solid particulate from a gas stream (dust collector).

Blinding: Dust blockage in a fabric or media that cannot be discharged by the cleaning mechanism.  This results in a reduced gas flow and an increased pressure drop across the media.  Once enough material has built up, airflow is severely restricted and the bags have to be replaced.

Bridging: The accumulation of dust collected between two of more filter bags.

Can Velocity: In a dust collector with the filter elements suspended from the tube sheet (pulse-jet).  Upward air stream speed calculated by dividing the open cross sectional area of the baghouse (less the area of the filter bags disc bottom) into the full volume of the exhaust fan (ACFM/Ft² = feet per minute).

Clean Air Plenum: The baghouse area through which gases are directed, located on the clean side of the filter bags.

Collection Efficiency: The measure of a dust collector’s ability to remove particulate from the inlet gas, typically expressed in percent or emission rate (grains per cubic foot).

Dewpoint: The temperature at which condensation begins to form as the gas is cooled.

Diaphragm Valve: A compressed air valve operated by a solenoid valve that opens to allow a pulse to a row of bags.

Dirty Air Plenum: The baghouse area through which gases are directed, located on the dirty side of the filter bags.

Differential Pressure: The change in pressure or the pressure drop across a device (baghouse) located within an airstream.  The difference between static pressures measured at the inlet and outlet of a device.

Dust Cake: A dust buildup on the filter bags that increases the efficiency of the filter media.

Dust Collector (See Baghouse)

Dust Loading: The weight of solid particulate suspended in an air stream, usually expressed in grains per cubic foot or grams per cubic meter.

Emissions: Particulate that escapes through or around a baghouse into the atmosphere.

Fan: A device for moving air and dust through a ventilation system.  If the fan is on the dirty air side of the baghouse, it is called a positive system.  If the fan is on the clean air side of a baghouse, it is called a negative system.

Filter Media: The permeable barrier utilized in a fabric style dust collector on which the dust cake is supported (bag).

Hopper: The section of a dust collector located below the filter bag housing utilized for the accumulation and discharge of the collected dust.

Impingement: The physical contact of a dust laden gas flow against a filter media.  Typically referred to the abrasive wear caused by this impact.

Interstices: The openings or voids in a filter media.

Interstertial Velocity: Velocity of a gas as it passes between a compartment of filter bags calculated at its highest value.  (See “Can Velocity” for formula)

Magnehelic® Gauge: An instrument used to measure the differential pressure drop in a baghouse.

Manometer: A U-shaped tube filled with a specific liquid.  The difference in height between the liquid in each leg of the tube gives the difference in pressure on each leg of the tube – used to monitor differential pressure.

Micron: A unit of length, 11/1000 of one millimeter (1/24,000 of an inch).

Negative Pressure Baghouse: A system where the fan is located after the baghouse on the clean air side, pulling air through the system.

OEM: Original Equipment Manufacturer.

Particulate: Any airborne solid material.

Permeability: A measure of fabric porosity of openness, expressed in cubic feet of air per minute per square foot of fabric at a 0.5” w.c. pressure differential.

Photohelic® Gauge: An instrument used to measure the differential pressure drop in a baghouse and to initiate the cleaning system by means of adjustable “high” and “low” set points for automatic actuation of a sequential timer.

Positive Pressure Baghouse: A system with a fan located prior to a baghouse on the dirty side, pushing air through the system.

Precoat: Material added to the air stream at start-up to aid in establishing the initial dust cake on the filter bags.

Pressure Drop: A measure of the resistance the gas stream encounters as it flows through the baghouse.  It may refer to pressure differential across the media, across the baghouse, or the pressure drop across the entire system, depending upon the points of measurement.

Pulse Cycle: The interval of time between pulsing one row of bags and pulsing that same row again.

Pulse Duration (On-Time): The length of time a pulse lasts, generally described as the length of time the electrical signal holds the solenoid pilot valve open.

Pulse Delay (Off-Time): Elapsed time between pulses in a dust collector cleaning system.

Pulse Clean Baghouse: A baghouse using short intermittent pulses of compressed dry air to clean dust from the filter bags.

Re-entrainment: The phenomenon where dust is collected from an air stream and is then returned to the air stream.  This occurs when dust is dislodged from a filter bag during cleaning and is again captured by the same or an adjacent filter bag.

Reverse Air Baghouse: A dust collector where cleaning is accomplished by mechanically, and temporarily, preventing the dirty gas flow into a compartment or group of filter bags while blowing low pressure cleaning air through these “off-line” bags in the opposite direction of typical air flow, to dislodge the accumulated dust cake.

Rotary Airlock Valve: Device having a star wheel (rotor) designed to provide an air tight seal between the negative or positive pressures of the collector and the outside atmosphere.

Screw Conveyor: A revolving screw operating in a fixed trough for conveying material from one point to another.  Note: Should a screw conveyor be used in a dust collector system, an airlock is still required to ensure ventilation air does not bypass through the conveyor.

SCFM: Standard cubic feet per minute.  The volume of gas flow per minute at standard temperature and pressure conditions (70°F @ sea level).

Shaker Baghouse: A dust collector where cleaning is accomplished by manually or automatically shaking the bags to dislodge the accumulated dust cake.  Typically, the airstream within the baghouse is in a static condition during the shaker cleaning cycle.

Solenoid Valve: An electro-mechanical plunger device that is either “normally open” or “normally closed”.  In use with a baghouse, it is for the relief of air pressure to activate a compressed air device such as a diaphragm valve.

Timer, Sequential: An electrical mechanism that activates a dust collector’s cleaning system.

Tubesheet (Dust Wall): A steel plate to which the open end of the filter bags are connected.  This wall separates the clean air and dirty air plenums of the baghouse.

Venturi: A cone-shaped device located at the top of a tubular filter bag in a pulse-jet dust collector which creates a negative pressure at the top of the venture for pulling additional air down into the filter elements during pulsing.

Weight (Media): The average weight per square yard of fabric.