Bag filters are used in a variety of industries, usually manufacturing industries that produce harmful by-products that need to be filtered out of the air, or in some cases, out of water. These industries rely on bag filters to limit pollution from their plants, or in water reclamation systems, to remove glass or metal particulates from various fabrication processes. Bag filters are often used in large mechanical arrays that filter air used in various manufacturing processes; the bags catch the dust, smog, or other pollutants created, and are cleaned periodically, then eventually replaced.
What Are Bag Filters?
Bag filters are incredibly simple, from a design point of view. They tend to look like very long tube socks, with a mounting ring at the top for hooking onto various systems like dust collectors and water filtration systems. They are made from a variety of materials, such as polypropylene and polyester. Bag filters work on the same principle of physical restraint that a fish net does, simply with much small pores in the material. In this article, we will cover the basics of bag filters, the materials they are made of, and what to look for when buying.
Main Components of a Bag Filter
A bag filter consists of the filter itself, which is a long tubular mesh made of a synthetic material such as polypropylene felt or polyester felt, and the top ring or rings, which are also usually made of a somewhat malleable plastic. Different bag filters use different style of rings, which are used in mounting the bags to the dust collector or other industrial machine. Manufacturers make bag filters in a variety of sizes for different machines, from less than a foot in length, to several feet for large dust collector and industrial applications.
Types of Bag Filters
Bag filters are mainly differentiated by size, and materials used in their construction. The filters themselves are usually made of synthetic materials such as polypropylene, nylon, and polyester. Different materials prove more efficient in certain applications, hence the variety of They are available in a variety of sizes that are fairly standardized (though by no means universally) across the industry. One of the most important things to consider when looking at various bag filters is the micron rating of the bag. You want to choose a bag with a micron rating that is appropriate for the size of particles you are attempting to filter out.
Standard Bag Filters
A standard bag filter is usually made from either polypropylene or polyester and are typically available in a variety of sizes, with the most standard widths being four inches and seven inches. Lengths tend to vary from nine inches to thirty-two inches, or even more in some cases. Some differentiators to look for include regular vs glazed polypropylene felt. In the case of glazed felt, the extruded polypropylene is subjected to heat, which melts and smears the fibers together, making for a denser filtration matrix.
High-Efficiency Bag Filters
Some companies offer high-efficiency filters, which typically contain more layers, hence more surface area. Filters like this work like large mazes, or labyrinths. Particles flow into the bag, and begin making their way through the dense filter maze, becoming trapped in various cul-de-sacs within the material. High efficiency filters can boast filtration rates well over 90%, making them the best choice for tough jobs or when working with especially dangerous contaminants.
Dust Collection Bag Filters
One of the most common applications for bag filters is in dust collection machines used in industrial manufacturing. During smelting or other manufacturing processes, pollution is generally created, and needs to be taken care of by the factory to some degree in order to be in accordance with environmental laws. Massive arrays of bag filters are often used, sometimes with dozens of filters working in tandem with one another to pull carbonaceous ash, smoke, VOCS, and other dangerous contaminants out of the air.
Liquid Bag Filters
Bag filters are great for water filtration as well, often being used in water reclamation systems that use CNC machines or water jets to cut through metal and other materials. Glass manufacturers also rely on bag filters to clean out glass shards and dust from the water stream they use in the fabrication process..
Specialty Bag Filters
There are many applications for bag filters outside of these regular industrial uses. One could use bag filters in residential applications, and many home beer-makers and vintners rely on bag filters during their brewing or wine-making process. Other bag filters are made of specialty materials, such as nylon monofilament mesh, which is desirable in some applications.
How Bag Filters Function
Bag filters work in the same way that a net works–it is a mechanical filter that works solely on principles of physical restraint. The water or air flows through the bag filter, while the particulate matter in either medium is filtered out, trapped in the dense weave of the filter.
Efficiency of Bag Filters
Bag filters are highly efficient, usually somewhere between 90% and 99%. How efficient a bag filter is depends on many factors, most importantly the size and nature of the contaminant you are attempting to filter out. Know your filtration goals, and the rough size of particulate matter that you are dealing with. Other factors that will determine how efficient a filter is are micron rating and material used to construct the filter. Different industries often tend to prefer a specific media type for their filters, because they have found, through long empirical testing, that it works best.
How to Select the Right Bag Filter
A bit of research into the specific contaminant you are working to remove, and the industry perspective on various media should give you enough to go on. These filters are used in a wide range of industries, and there is a host of free information online and on YouTube discussing the relative merits of various filter media, and what works best for what application.
Application-Specific Requirements
Ensure that you have determined the best filter for your application. In general, there are no hard and fast rules when it comes to water and air filtration–everything is context-specific, and depends on the contaminants you are attempting to isolate and remove.
Performance Criteria
Some of the things to consider when purchasing are the track record of the company and filter type, its proven efficacy in combating the problem you are facing, its lifespan and durability, and its cleanability. Especially in air filtration contexts, bag filters are cleaned and reused for quite a while in some cases before being reused, so determine the average expected lifespan for your application.
Cost vs. Efficiency
High efficiency filters, or specialized filters, are typically more expensive than standard bag filters, though for many people and applications, the extra filtration power may not be strictly needed. Determine what you need, and buy at the best price point, rather than automatically reaching for the top shelf option.
Maintenance and Troubleshooting
Maintenance on bag filters typically consists of routine cleaning, and eventual replacement. When installing a bag filter, you may find that various manufacturers have bag filters that are sized slightly differently, though they are fairly standardized across major manufacturers. Ensure that you are choosing a bag with the same ring size and type so that it fits your application.
Conclusion
While they are mostly seen in industrial contexts, bag filters can be used in a variety of contexts and ways, even in some home uses. They are quite cheap, inasmuch as polypropylene and polyester are abundantly available and easy to produce, and they are effective as well. Do your homework, and make sure that you have the correct size, micron rating, and material for your needs, and then sit back and let your filters work.
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