Precoating Information

Precoat is a chemically inert light density powder that is injected into the baghouse to establish a uniform porous dust cake on the filter bags for maximum even air flows with enhanced operational efficiency and unequaled bag protection from moisture, particulate bleed through, hydrocarbon carryover, bag blinding, oil and tacky or viscous contaminants.


Procedure Steps for Filter Bag Precoating

The amount of precoat utilized should be a minimum of 1 lb per 20 square feet of baghouse filter cloth area. For cartridge filters, 1lb per 100 square feet of media. (use the same formula as the Leak Detection Powder Information to find the sq. ft. of the media).

Prior To Injection of Precoat

  1. Ensure that all previous dust has been evacuated from baghouse hoppers, and then turn off hopper dust removal equipment.
  2. Deactivate (lock-out) the bag cleaning cycle to prevent filter bag cleaning during the precoat period.
  3. Operate system at approximately 50% of design air flow to the baghouse for resulting air flow velocity of approximately 2000 feet per minute through the inlet duct, but not less than 2000 feet per minute.
  4. Inject precoat at the feed rate of .3 lbs per minute per 1000 ACFM of reduced gas flow to the baghouse (EX. 50,000 ACFM to baghouse/1,000 ACFM x .3 lbs. = feed rate of 15lbs per minute.)
  5. For baghouses operating under suction, precoat can be injected through ports or inspection doors in ducts or hoppers.
  6. For positive pressure baghouses, precoat should be injected into duct at the suction side of the positive pressure system fan.
  7. Isolate each compartment and inspect filter bags for adequate precoat cake, (approximately 1/26” thick) and check inside of hoppers to be sure there is not a large amount of precoat dropout.
  8. Once filter bag precoating with precoat is complete, increase the air volume for normal design flow levels to the baghouse, and turn on the hopper dust removal equipment. However, do not reactivate the filter bag cleaning cycle until a minimum differential pressure of 3”-4” s.p.w.g. is measured across the bags. This ensures that a seasoned cake of Precoat has been achieved on the filter bags prior to activation of the initial cleaning cycle.

Why, When & How to Precoat Filter Bags & Cartridges

Benefits of Coating
  • New filter media is porous and fine particles 0.5 micron or smaller will leak through the filter media. The precoat starts a cake on the filter media. Our precoat is made up of 50-60 micron particles. This base cake helps prevent blinding and clogging of the new filter media.
  • Also used as a spark and flame retardant. Some of our customers re-precoat for just that reason.
  • Precoating is helpful for air containing moisture or hydrocarbons.
  • Depending on the application, precoating can extend the filter life.