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How to choose a liquid filter bag?

Time: 2022-02-08

I often receive inquiries from customers. Many customers know what they want to filter, but they don’t know how to choose filtering products. In fact, the choice of liquid filter bag should be combined with its own needs, such as: what effect should be achieved by filtering? How many micron particles should be intercepted? How much flow should be filtered per hour and so on.

First of all, it is necessary to understand the filtration mechanism of the bag filter system: the liquid flows from the filter bag to the outside of the bag, and the filtered particles are trapped in the bag. The working principle of the bag filter is pressure filtration. The bag filter system mainly includes three parts: filter container, support basket and filter bag.


1.) Selection of Filter Bag Material:

First, according to the chemical name of the fluid to be filtered, find out the available filter material according to the chemical combination taboo, and then according to the filter medium temperature, operating pressure, pH value, viscosity (CPS), impurity types such as (hard particles, soft particles), impurities Content (PPM), operating conditions (such as whether it needs to withstand steam, hot water or chemical sterilization, etc.), evaluate one by one, and reject inappropriate filter media. Use is also an important consideration. For example, the filter material used for drugs, food or cosmetics must be FDA-approved; ultrapure water must be pure, and the filter material that does not contain emissions that will affect the specific impedance; filter gas must be Choose hydrophobic materials and whether you need a “sanitary filter” design, etc.


2.) Selection of the Precision of the Filter Bag:

This is one of the most troubling questions. For example, to remove particles visible to the naked eye, use 20- or 25-micron filter bags; to remove clouds in liquids, use 1- or 5-micron filter bags; to filter out the smallest bacteria, 0.2-micron filter bags are required. The problem is that there are two filter accuracy units: absolute accuracy/nominal accuracy.


Absolute Accuracy/Nominal Accuracy

Absolute accuracy refers to the ability to filter out 100% of the particles with the indicated accuracy. This is an impossible and unrealistic standard for any filter material, since 100% is an infinite value. Strictly speaking, the absolute filters commonly known on the market, such as membranes, can only be called “close to absolute” filtration, while others belong to the nominal accuracy. Nominal accuracy, this is the main trouble: “Nominal accuracy is not a standard recognized and followed by a common industry.” That is to say, Company A can set the nominal accuracy at 85-95%, while Company B would rather set it at 50-70%. In other words, company A’s 25-micron filtration precision may be equal to company B’s 5 microns, or finer. For this problem, an experienced filter bag supplier will help with the choice of filtration precision, and the fundamental solution is “trial “.

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