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Filter Pre-Coat Application
How & Why

The application of any filter pre-coating media is very much the same in most cases. Depending on the product details may change. The main reasons for applying a filter pre-coat are to provide an improved efficiency not normally possible with a clean, new filter media, and to help prolong the active life of the filters. A pre-coat medium will tend to partialy plug and coat the open pores in a filter product. This plug will be sufficiently porous in itself to have a minimal effect on air flow through the filter, but will have reduced the available air passages in size, limiting the amount of particulate emissions.

This also has the desirable effect of preventing the particulate from plugging the air passages with a non porous mass.The combined effect of the cleaning cycle and continious bombardment of particulate, does eventually overcome the protection of the pre-coat, but the working life of the filter is usually extended noticably.

Pre-coating products are usually applied to new, unused filters installed in the system, with any cleaning mechanism turned off.

When applying a dense pre-coat to a needlefelt type filter, such as Diatomaceous Earth or Lime, the fan is usually dampered down to 2/3 to 3/4 the normal volume. This is to reduce the filter face velocity and apply the pre-coat gently. New filter media is comparatively wide open and it is not the intention to blind the media. Needlefelt is a depth filtering media that relies on collected product partially penetrating & plugging the felt, in order to reach higher filtration efficiencies. On the other hand, with a Pearlite type of pre-coat, dampering is not so critical as Pearlite is a very porous product, which will allow reasonable airflow even when applied quite thickly.

Woven fabrics, and cartridge filters are usually a lightweight fabric, and tend to be surface filtration products. This means that any product collected remains on, or very close to the surface of the media. In this case, fan dampering again is not quite so critical.

Fan dampering is not necessary withAMORPHOBE ™. Particle size is small enough (0.3 microns) to get into the body of the fabric and form a porous coating. Also, this tends to spread the desirable hydrophobic properties more evenly throughout all the available air passages. AMORPHOBE ™ is applied at the very low rate of 1 lb for every 500 sqft for cartridge filters, and 1 lb for every 400 sqft for fabric filters.

Any pre-coat can be introduced at the closest pick-up point to the filter system by means of a cup or pail, or can be sucked directly from its shipping container, usually a paper sack. When pickup hooding or location prevents easy access for pre-coat introduction, an alternative location could be the hopper discharge This only works on suction systems, ensure the fan is on the clean side of the system. For a pressure system (fan on dirty air side), the main duct leading into the fan is a convenient spot to put a pre-coat feed opening.
When the pre-coating is complete, put the system on line and introduce the fume, dust or other particulate. If the fan was dampered, now increase to full volume.
Depending on the system, it may not be necessary to turn on the cleaning cycle until the pressure drop reaches 2" or even 3" W.C. but this should be determined with the regular operator of the system or maintenance department.

If you have questions on pre-coating, or any other filtration problem, please do not hesitate to contact us, it is our pleasure to help.

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