What is a Filter Micron Rating?
Filter micron rating refers to the size of particles that a filter can effectively capture. It is a measure of the filter’s ability to remove contaminants of a specific size from a fluid (liquid or gas) that passes through it. The rating is usually given in micrometers (μm) or micron.
It’s worth noting that the effectiveness of a filter is not solely determined by its micron rating; factors such as the filter material, particle shape, and application also play crucial roles.
Some Important Considerations for Selecting Filter Micron Rating
Physical Properties of Particles
Particle shape and size are equally important for the selection of micron rating. Testing models rely on spherical or cylindrical shapes but particles in industrial applications are rarely uniform and cannot be fully described by a single dimension such as a radius or diameter e.g. a needle like particle will have a diameter much smaller than overall length.
Application Requirements
An application might require removal of all particles or only a percentage of particles above a certain micron rating.
Filter Type
Different types of filters (e.g., depth filters, surface filters, membrane filters) have varying capabilities in terms of particle retention.
Filter Materials
Some materials are better suited for specific types of contaminants e.g. a thicker non woven media will provide better removal of deformable particles.
Cost
As a rule of thumb, the finer the micron rating, the higher the cost of replacement filters. The effective surface area for filtration can also decrease with very fine micron ratings and a fine filter will require larger surface and prefiltration to avoid frequent filter replacement.
Regulatory compliance
In certain industries, there may be regulations specifying the required level of filtration e.g. honey, cryptosporidium.
Micron Ratings of Some Common Particles
Coffee
Iron Oxide
Silt
Yeast
Pollen, honey
Bacteria
Hair
Red Blood Cell
Sand, fine
Sugar
100 - 500µm
20 - 100µm
20 - 50µm
3 - 40µm
20 - 80µm
0.2 - 10µm
50 - 200µm
2- 8µm
100µm
50 - 400µm
Commonly Used Methods for Selecting Filter Micron Rating
- A small scale onsite trial is by far the best method to select the correct filter media and micron rating for challenging applications.
- A sample can be tested for particle size distribution and particle concentration analysis.
- More commonly, filters are selected using data from previous experience of similar applications or from filters currently in use in customer’s process.
Micron Ratings for some Common Applications
Industrial Applications
Parts Washing
Parts washing can be a multi step process that uses a mix of cartridge, bag and oil removal filters with a filtration range of 1 - 100μm.
Waste Water
Suspended solids can cause siltation and blockages in the sewerage system. The UK Environment Agency has a default permit standard for suspended solids of 100mg/l.
Sidestream Filtration
Removal of magnetite, sediment and biological growth in LTHW and CHW is usually achieved with a magnet + 5μm filters.
Paints and Coatings
Filtration is often a solution to quality problems. Due to the large number of paint formulations and raw materials, filtration will depend on the application.
Solvents
Solvents are widely used in manufacturing processes. Hydrophobic 0.2 micron membranes for sterile filtration or 1 - 100μm elements or bags for particulate removal.
Heat Exchanger
Suspended particles can cause rapid fouling of heat exchanger plates, resulting in frequent cleaning or costly plate replacements. 50 - 200μm.
Pumps
Filter micron rating can range from 25 - 500μm depending on application and pump protection requirements. These are usually mesh baskets or filter bags.
Waste Vegetable Oil (WVO)
Particulate removal from waste vegetable oil (WVO) is a common application in biodiesel production. 100 - 200μm mesh baskets or filter bags are commonly used.
Fuels & Biofuels
5 - 100μm filter bags can be used for particle removal from Diesel and Biodiesel blends.
CNC & Cutting Fluids
Abrasive particles in coolants can cause tool failure, nozzle damage, reduce coolant life and impact surface finish. Filter selection is based on finish requirements.
Food Grade Applications
Bacteria
Bacteria removal is required in many beverage and pharmaceutical applications. Usually 0.2μm in pharmaceuticals and 0.45 - 0.65μm in beverages.
Beer
Beer filtration is a multi stage process which involves removal of sediment, hop, haze, yeast and spoilage organisms. Micron ratings range from 0.45 - 10μm.
Whiskey
Whisky is filtered to remove barrel char, barrel sediment and unwanted particles. This is also used to achieve a consistent product. Filters range from 1 - 10 μm.
Kombucha
Kombucha is fermented tea. Filtration is used to improve the appearance and quality of final beverage. 10 - 100μm filter bags or mesh baskets are commonly used.
Bottled Water
Bottled water production is a multi stage process. Filtration is used to remove suspended impurities (1 - 5μm) and also to keep storage tanks sterile (0.2μm)
Honey
Commercial honey blends require filtration prior to bottling in order to remove contaminants and to maintain consistency. Usually 100- 200μm.
Flavours
Filtration is used to clarify juices, syrups and alcoholic beverages to eliminate impurities and ensure a consistent and high-quality flavour profile. Application dependent.
Tea Infusions
Tea is infused with leaves and herbs to extract flavours, aromas and colours by seeping ingredients in hot water. Draw string filter bags can be used as large tea bags for infusion. Micron rating depends on size of ingredients.
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