By Mark Belcher, Donaldson Torit Filtration Engineering Manager
Haopeng supply professional and honest service.
Filter pre-coating is the practice of intentionally loading a porous particulate layer onto a filter media in a dust collector to enhance some aspect of performance. For reasons discussed below, pre-coating is sometimes considered advantageous for pleated cartridge filters, but you may not find it to be the best choice for many applications.
There are two basic reasons pre-coating would be considered for new clean filter media. Before considering the possible use of pre-coating, you should understand the differences and impacts of it, including how a single application of pre-coating may only be a temporary fix.
Pre-coating is often suggested as a means of increasing the initial efficiency of lower performance filter media. New, unused cellulose or cellulose-synthetic blend filter medias often offer initial efficiencies of only 30% on sub-micron particles (based on ASHRAE 52.2 testing). The filtration efficiency performance does gradually improve as dust is deposited on the media (as it’s loaded), but this enhanced efficiency performance can be accelerated with the use of pre-coating. As the pre-coating builds a layer of particulate on the surface of the filter media, it acts as a pre-filter, capturing submicron and other particles from the airstream before they can penetrate into the filter media, so overall filter efficiency improves.
Pre-coating suppliers often suggest amounts of pre-coating material application, from as little as 0.5 lb (or 227 grams) of pre-coating per cartridge filter to up to 2.5 lbs (or 1,134 grams) of pre-coating per filter. It is worth noting that while the addition of pre-coating to the filter can increase initial efficiency, the addition of pre-coating also means there will be an increase in filter restriction to airflow. Depending on the type and amount of pre-coating, this increase in filter restriction can become very significant and the increased pressure drop will require more energy to move air. Additionally, there is a cost associated with the application of the pre-coating, as well as the disposal of the secondary waste stream.
Pre-coating filter media for enhanced filtration efficiency is only a temporary fix. Cartridge collectors typically extend filter life by using compressed air cleaning pulses to periodically remove accumulated “dust cake” from the surface of the filter media. When cartridges are pulse cleaned, substantial amounts of collected particulate and pre-coating materials are both dislodged and removed from the media surface. The media once covered by pre-coating now behaves more like untreated filter media. The efficiency adjusts accordingly because the filter media is exposed to fine particles that can penetrate into and bleed through the media.
The end of life for filter media occurs when pressure drop across the filter media becomes either high enough to substantially restrict airflow or the increase in energy cost to operate the fan against the increased resistance reaches such a level it becomes impractical to continue to operate the fan with plugged filters. The general logic behind claims of extended filter life through pre-coating is dependent on the assumption that pre-coating minimizes the amount of small particles penetrating into the depth of the filter media (minimizing the rate of plugging for the media). That may be a reasonable assumption immediately following the application of pre-coating material because the pre-coating material acts as a barrier to smaller particles entering the actual media. However, as discussed earlier, any pulse cleaning of the filter media will disrupt that barrier, and since the pre-coating is removed with each pulse cleaning, its benefits are also removed. After pre-coating has been disturbed and lost during pulse cleaning, the filters begin to load just like untreated filters, and the operating pressure drop again begins to increase accordingly as the media begins to plug, see Figure 1.
Of the premium grades, fine fiber filters offer the best option in most cases. Medias for premium filters with fine fiber are composed of a substrate (often similar to generic cellulose cartridge media) with a permanent surface layer of fine fibers. This layer is often less than one micron thick, so plugging or depth loading in this layer isn’t an issue. The premium fine fibers on high quality fine fiber cartridges will be fine fibers, usually measuring 0.3 microns or smaller in diameter, and they will form a permanent matrix of small pores on the surface of the filter media. Because the fibers in the surface layer are so small in size, they don’t noticeably increase the resistance to air so initial pressure drop stays lower.
If a user wants higher initial efficiency, fine fiber filters are an excellent option. Efficiency of a clean and new fine fiber cartridge will be much higher than a generic cartridge; typical fine fiber cartridges are at least 65% efficient on sub-micron particles while a generic filter may struggle to achieve 30 % initial efficiency, and operating efficiency for the fine fiber filter will increase very quickly. ASHRAE 52.2 testing demonstrates that after one ounce (or 28.35 grams) of particulate is fed to a fine fiber cartridge, its sub-micron efficiency can easily exceed 90%.
Users also seeking longer filter cartridge life will benefit from the use of premium grade fine fiber filters. In operation, dust loads on the surface of the fine fiber media. When the media is pulse cleaned, most of the dust cake is dislodged from the media and is removed from the filter. The fine fiber layer though remains intact, and continues to protect the substrate from depth loading and blinding. Because depth loading is no longer significant, the fine fiber cartridges continuously clean to a lower operating pressure drop than any of the other media options, and produce significantly longer life, see Figure 3.
Hydraulic systems are becoming increasingly complex, and their filters need to keep up. Filtration is key in keeping your hydraulic system working properly by preventing particle contamination from disrupting its performance. Hydraulic filters come in two main options: metal mesh and fiberglass filter media as per this post’s topic. Though they share a common goal, each type of filter has their own advantages and disadvantages that make them suitable for different applications.
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In this post, you will explore the basics of both metal mesh and fiberglass filters. The modern hydraulic oil filter comes in two varieties: metal mesh and fiberglass: both of which protect your equipment from contamination. Each filter will usually consist of a mesh or fiberglass element, designed to trap particles that could cause wear or malfunction to sensitive components.
Airborne pollutants, rust and other contaminants are the enemies of hydraulic systems, affecting component performance and lifetime. Choosing an efficient filter material is essential for protecting sensitive components from faulty operation or even complete failure. Hydraulic oil filters come in two major forms: metal mesh media and fiberglass media. Each comes with its own set of advantages and disadvantages. Understanding which is more suitable for your hydraulic system starts with knowing the basics of both types.
Metal mesh, also known as honeycomb, is a better option for filtration than other types of mesh. It is lighter, stronger, and easier to clean. It has many ways of use: from making window screens or mosquito nets to filtering water. Metal mesh is a more effective filtration option than any other material. The main reasons:
Metal mesh is a better option than alternatives like fiberglass, because it can filter out heavy metals, which are potentially harmful to your health. Metal mesh has no such dangers associated with it. It has metal rods shreds together that have been ground down into very small pieces so that they fit together like puzzle pieces without any sharp edges or points where things might get stuck in between them all together.
Metal mesh filters can reduce energy consumption by filtering out large amounts of waste material from a water source before it enters a home or business building’s plumbing system. This means less power is in use to run these systems compared to traditional systems that do not include metal mesh filters. The main disadvantage to using this type of filter is that they tend to take longer than other types because they have so many holes through which water must flow before it reaches ground level where it exits into another container or drainage system outside your property boundaries.
Metal mesh and fiberglass hydraulic filters are typically made from either stainless steel or aluminium. Both materials have advantages and disadvantages regarding their environmental impacts. Stainless steel has a lower carbon footprint than aluminium because it is not from raw materials such as oil or coal. However, it does require additional processing steps during manufacture that can result in higher emissions than those produced by aluminum. Aluminum has a lower carbon footprint than stainless steel because it has recycled material rather than new raw materials such as petroleum products. It requires more energy to produce than stainless steel does.
Metal mesh and fiberglass hydraulic filters are typically more expensive than other types of filters, especially when compared with paper or plastic media filtration systems. It requires more processing steps during manufacture and generally costs more per unit volume due to its higher cost. Metal mesh and fiberglass hydraulic filters are both effective ways to remove particulate matter from water. However, they have a few important differences:
Metal mesh and fiberglass hydraulic oil filters operate in a variety of environments. However, they also have some specific needs that need to be considered when making decisions about their use. These filters are in areas with harsh flushing conditions, such as oil refineries and natural gas wells. In these situations, the filters should be able to withstand strong hydrostatic pressure and corrosive chemicals that can damage the filter elements. These filters are built for durability and longevity over time. It is important that these filters be able to withstand extremes of temperature without failing due to improper design or poor manufacture quality control standards. Contact us for more information about filters.
Hydraulic mesh filters last longer because their stainless steel or metal construction resists wear and tear, while fiber filters degrade faster due to clogging and material breakdown.
Hydraulic mesh filters improve efficiency by maintaining consistent flow and trapping contaminants without restricting fluid movement, whereas fiber filters can become saturated and reduce performance.
Hydraulic mesh filters require less frequent replacement because they can be cleaned and reused multiple times, whereas fiber filters must be replaced once they reach their dirt-holding capacity.
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