Terms & Formulas

Abrasion

Wear on bags/cloth due to excessive bending, filtering or product “blasting” the bag.

Dewpoint/ or Acide Dewpoint

The temperature at which liquid condenses in the bag house and/or on the bag.

Bleeding/ Bleed

Product particles or fume leaking (bleeding) through the bag.

Blinding

Product particles impacting filter media (bags) and closing the media pores reducing air (gas) glow and/or increasing pressure drop in the system.

Bridging

Collected material build-up across an opening blocking airflow or cleaning. Example: Hopper outlet or between bags.

Cake

A layer of dust that is allowed to build up on surface of the bag to enhance filtration. Generally this is only required on depth filtration style bag media.

Cloth

Sometimes called media, medium or fabric. The combination of textile fibers to create a filtration cloth that will be converted into a filter bag.

Cloth Weight

Generally the weight per sq. yd. or sq. ft. of a specific cloth. Often used to identify weight and airflow characteristics for a cloth (media).

Gas to Cloth Ratio

Also called air to cloth ratio. The volume of gas (air) entering the dust collector (ACFM) then divided by the total sq. ft. of cloth area in the bag house of filter section.

Total Inlet Volume of Gas (ACFM) | Total Cloth Area (FT2)

How to figure total cloth area:

(Bag diameter (in.) x 3.14 x bag length (in.)) / 144 x total number of bags.

Example:

Bag diameter:

6″x 3.14 x 120″= 2,260.8″

2,260.8″ / 144= 15.7′ of cloth per bag x number of bags (100)- 100 x 15.7= 1,570 sq. ft. of bag material in the collector.

When doing your calculations or ordering bags, be sure to remember:

Circumference: Distance around a circle, bag.

Diameter: Distance across a circle- across a rounded bag or cage.

Flat Measurement: Across the bag laid flat.

Particulate

Dust particles.

Permeability

The measurement of the fabric’s openness or porosity. Used when selecting proper media for filtration and operating pressures- CFM of air/sq. ft. of fabric at 0.5″ of H20 pressure differential.

Permeability Test

A test used on new materials for airflow as above. Also used on dirty filters to check blinding and again on cleaned filters to measure the airflow on the cleaned filters against the new filter medias airflow.

Pre-Coat

Materials added to the air stream on initial start-up to and in building the initial dust cake. Some pre-coats include calcium oxide, quicklime, burnt lime, perlite, diatomaceous earth or a combination of these and other additives to assist the new bag.

Seeding

Inducing a coarse, dry dust to the bags prior to full start-up – similar to pre-coating but sometimes done with process particulate (dust).

Shaker Bag House

Bags are cleaned by shaking during periods of down time or when no inlet air is present.

Snap Band

A flexible stainless steel band, covered with material. The snap band is found on the open end of a bag and “snaps” into a hole in the tube sheet section of the bag house, creating a seal between the dirty and clean sections in the bag house.

Tensioning

The amount of tension applied to a shaker bag for proper operation and reduced wear – rule of thumb is 2 lbs. to 2.5 lbs. per circumferential inch of the bag.

Tube Sheet/ Cell Plate

A tube sheet can be at either the top or bottom of a collector and is a fabricated metal sheet with close tolerance holes punched or laser cut to facilitate a bag snap band or bag and cage assembly.