TERMS & FORMULAS

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

DEWPOINT/OR ACID DEWPOINT: The temperature at which liquid condenses in the bag house and/or on the bags.

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) flow 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 to 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 or 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 –
number of bags – 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 H2O 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.

PRESSURE DROP: Resistance of airflow creating a pressure differential across the cloth, bag house or system. An installed and maintained magnehelic meter is an excellent indicator of pressure drop and loss of efficiency.

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. See our example for proper snap band installation in bag lady tips.

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 – see bag lady tips for chart.

TUBE SHEET - Also known as 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.