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Bag filters – often the first step in the filtration process

2 Minutes Read

Bag filtration technology has many applications when liquid process streams enter a manufacturing site or a process. We explain some essential features of bag filters technology so that you can apply them correctly.

Are bag filters just a different type of strainer?

Although the shapes of the bag filter and strainer fitted into a housing in the process line are similar, the similarities stop there. Both are filters but are used for entirely different applications. The strainer is the first line of defence filter due to its construction from metal meshes. It would remove particulate and debris that might damage further filtration downstream, such as a bag filter if they remained in the liquid stream. The bag filter is general-use filter technology for removing particulates and contamination that is simple to use, and bag filters are easy and rapid to change.


Where are bag filters typically used?

A typical application of bag filters in industrial, water and food applications is removing coarse and fine particulate, carbon or resin fines and sediment above 20 microns in size. This protects the downstream process equipment and recontamination of the liquid stream. Also, by removing these contaminates early in the process, we extend the service life of fine filtration and other separation technologies while reducing the customer’s annual cost of filtration.

What is the correct liquid flow rate for different bag filters sizes?

Standard bag filters come in four sizes known as 1,2,3 and 4. Typically, size 1 (7” diameter and circa 16”) handles flows up to 20 m3/hr and size 2 is twice the length (7” diameter and circa 32”), managing twice the flow up to 40 m3/hr. 
However, for some reason, sizes 3 and 4 do not continue the same logic. Therefore, size 3 is the smallest product (4” diameter and circa 8”), suitable for flow rates to 6 m3/hr, and size 4 (4” diameter and circa 15”) is used on flows up to 12 m3/hr.


What materials make up bag filters?

Polypropylene is the main material in bag filters, but manufacturers also produce them in polyester, nylon, Nomex, and PTFE. The key reasons for the different materials are chemical compatibility with the liquids being passed through the bag and the bag’s maximum working temperature. Polypropylene has the lowest temperature resistance and is only used below 1000C. PTFE has the highest temperature resistance and is used in applications up to 2500C. 

What are the main applications of bag filtration?

Paint manufacture – removal of paint skin, agglomerates and particulates.
Sidestream filtration in HVAC applications in the building services industry – removing sediment, rust, and suspended calcium deposits from CHW, LTHW, and MTHW circuits.
Water treatment processes – protecting downstream equipment, such as valves, heat exchangers, and sensors.
Incoming water to manufacturing sites – sediment, coarse and fine particulate removal.

Bag filtration is a simple, economic, easy-to-install and uses filter technology that you see throughout many process industries as the first stage in a filtration train. Find out how Porefilter supports your bag filtration needs (bag filters, bag filter housings, duplex systems).

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David Keay