Filtration Glossary

Absorption
Process where one material consumes another as a homogeneous mixture in solution form

Air-to-cloth Ratio
The ratio of the amount of air entering the baghouse to the amount of surface area available for filtration. Optimal air to cloth ratios vary for different industry segments and types of dust collectors. Example: If the fan on a baghouse is capable of 100,000 CFM and the baghouse has 1000 bags of 6" diameter x 12' long (for a total filtration area of 18,850 sq. ft.), the A/C ratio would be 100,000/18,850 or 5.3:1

Blinding
Particulate that accumulates within and/or on the surface of the media such that the flow passages for the gas are blocked restricting the flow and resulting in high pressure drop.

CFM
Acronym for Cubic Feet per Minute. A unit of measure for volumetric flow.

Dust Cake
Essential buildup of porous dust layer on the surface of a filter, which significantly increases the efficiency of the filter. Proper management of the dust cake also effects useful life of the filter.

Epitropic Fiber
Filtration media manufactured by mechanically bonding layers of staple fibers to a base cloth (scrim) by means of a fiber interlocking machine. Needles are used in this machine to punch the fibers through the fiber mass and lock them to each other.

Needle Felt
Fabric structures constructed by the interlocking action of the fibers them- selves, without spinning, weaving, or knitting.

Hydrolysis
A chemical reaction in which water reacts with another substance, either dust or the filter media, breaking the chemical links and creating two or more substances.

Permeability 
A measurement of the ability of air to flow through a filter at a given differential pressure. The value is expressed as (U.S.) cubic feet per minute at .5" water gauge differential or (Metric) liter/min at 20mm water gauge differential.

pH
The measure in units from 0-14 of the acidity or alkalinity of a stream of gas or liquid. A pH of 7 is neutral. Values below 7 tend towards acidic; values above 7 tend toward alkaline.

Pressure Drop
Resistance to gas flow; may refer to apressure differential across the cloth, across the baghouse, or across the entire system. Units are usually inches of water.

Pulse-jet
Type of baghouse design where dust is collected on the exterior of a filter tube, supported by a cage, and cleaned with a rapid pulse of compressed air driven down the interior of the filter tube.

Reverse-air
Type of baghouse design where cleaning is accomplished by reversing the flow to a portion of filters and dislodging the dust.

Shaker
Type of baghouse design where the filter bag is agitated by mechanical means to dislodge the dust.

Scrim
The openly woven substrate fabric that forms the base of needle elts.This light weight woven fabric can be seen in the middle of the “felt sandwich” in a cross-section view. Many in the industry regard the scrim as reinforcing bar in the felt. They point to the scrim as being responsible for lending burst and tear strength to the needle felt.

Self-supported
A nonwoven fabric that has been processed to interlock the  fibers such that a scrim is not required. Self-supported filter materials have established themselves as the most popular choice for low temperature applications.

Glazing
High pressure pressing of the filter medium at elevated temperatures; fuses surface fibers to the body of the filter medium.

Singeing
Passing of the filter medium over an open flame, thereby removing the protruding surface fibers. Singeing the collection side of the filter allows for easier dust cake removal.

Staple Fiber
Short fiber cut to specific length in synthetics to either form yarns or non-woven felts. The size, distribution and type of fibers used in the filtration vary to suit process needs. Selecting the right combination is essential for maximum performance.

Tensile Strength
A measure of the ability of yarn or fabric to resist breaking by direct tension.

Thread count
The number of warp and filling yams in a fabric.

Warp
The yarn running lengthwise (machine direction)

Weft
Cross machine direction

PTFE Membrane
PTFE membrane is a thin film produced by expanding microporous polytetrafluoroethylene. The slick membrane surface provides excellent dust cake release. In the process of manufacturing the ePTFE membrane, microporous holes are opened in the membrane that permit the passage of gases but not particulate. These pores can be regulated to various sizes and applied to specific applications as required. Various thicknesses, efficiencies and pore size openings of ePTFE membrane can be manufactured to meet the most stringent requirements.