Choosing the Right Filter Bag

Choosing the right filter bag depends on many factors including application / process, micron rating and temperature & chemical compatibility. There is a wide variety of baghouse filter bags on the market.

Filter bags have a dirty side and a clean side; the dirty side captures dust and the clean side contacts and exhausts the cleaned gas stream. The bags have a sealing ring that prevents particulates from bypassing the bag.

Needle Felt

Needle felting is a wool craft that creates lifelike 3D figurines and flat pieces of art filter bag for use as wall decorations. It is a relatively new technique that uses needles to shape wool into a solid object. It is similar to wet felting but allows more precise design and a quicker process. Felting with needles is also easier for those with physical limitations.

Felting needles come in various gauges (size) and barb count. Those with higher gauge numbers will feel more quickly but leave larger stab holes in your work, while those with lower numbers are more finely-tuned and can be used for smaller projects. Felting needles also have different shaft shapes and types. Triangular needles have a basic three-barb design, while twisted needles spread the barbs out over a wider surface and allow faster felting. Cross star needles have four working edges and are useful for felting textured surfaces or attaching limbs to your figure.

Filter bags are often exposed to a variety of chemicals in industrial applications, which can damage the fabric and lead to poor filtration performance. Selecting a filter bag with a chemical resistance treatment, such as SlyTech-01, can extend the lifespan and improve the efficiency of the filter.

Snap-Ring

A snap-ring is a plastic ring sewn inside the filter bag opening that aligns with a groove within the support basket. The ring and the groove have tolerances to create a tight seal, holding the filter bag in place during use. The ring can be made from zinc, stainless steel or polypropylene. A variety of materials are used to make the ring, depending on the filter bags application.

The choice of material will be based on the particle size range and retention efficiencies required for your application. Needle felt materials are economical for 1 to 200 micron nominal rated efficiency, with limited depth filtration. Woven cellulose and aramid are available for higher flow applications. A special design, the LOFCLEAR model, is absolute rated for its ability to adsorb trace oils and entrap gel-like solids for automotive and coatings.

Melt-blown filter bags are excellent for 1/2 to 25 micron retentions, offering higher absolute rated efficiencies and a longer service life than needle felt or woven materials. They are manufactured using a melt-blown process that allows control of the density and thickness of fibers, with minimal change in performance over time. This also reduces the likelihood of fibers “migrating” downstream, as can be seen in a sewn construction. Additional filtration products, such as filter bag positioners and displacement balloons, can improve the performance of your system.

Crush-Ring

SNAP-RING filter bags use a metal or plastic ring sewn within the opening of the bag that aligns with a groove in the bottom of a filter vessel. The ring is usually made of either zinc, 316 stainless steel or polypropylene. The ring helps prevent bypass of fluids between the filter bag and the container. Using this type of seal will help reduce the number of times you need to replace your filter bags.

This is because it will reduce the amount of time you need to re-instate your filtration system when changing filter bags. The ring also allows the filtration bag to expand and contract with the pressure of the liquid flowing through the filter bag, which makes it more resistant to leaks.

Another advantage of this type of filter bag is that it will help reduce the frequency of pulsing your system, which geotextile manufacturer can damage the filter bags and the pulse valve solenoids and diaphragms. Pulsing increases wear and tear on your equipment, so less pulsing will save money in the long run by reducing repair and replacement costs for these components.

Using this style of filter bag can be a good intermediate solution between needle-felt, mesh and melt-blown. These are more expensive than needle-felt or mesh bags, but they provide better nominally rated efficiency and can eliminate fluid bypass.

Melt-Blown

Melt-blown filter bags are a highly efficient solution for applications where the minimalization of particle travel is key. This is due to their unique structure that features an inner/core layer of micro pores for efficient particle retention, with a coarse pre-filter layer for removal of large debris, and an outer cover that prevents fiber migration. This is possible thanks to the specialized manufacturing process that uses precise melting and extrusion of polypropylene (PP) material.

This unique manufacturing technique starts with raw synthetic thermoplastic materials such as PP or polybutylterephtelate (PBT), which are melted into liquid state and forced through small capillaries. The molten polymer is then blown by high-velocity hot air that creates a random web of fine fibers. The web can then be calendered to reach a specific thickness and pore size that can match the requirements of various industrial filtration systems.

The finer, more breathable woven fiber mats produced by melt-blown nonwovens offer a higher surface area per weight and moderate stiffness, while maintaining tunable permeability. In combination with the lower cost of production and good resistance to many chemicals, this makes it an ideal choice for a wide range of industrial filtration applications.

The filtration properties of PP melt-blown fabrics also make them suitable for medical and sanitary cloths such as surgical gowns, protective clothing, and sterilization wraps. This fabric is also often treated with electrostatic treatment to help boost the fabric’s ability to trap bacteria and viruses.