What is a line filter and how does it work?

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What is a line filter and how does it work?

When working with compressed air, air treatment is crucial to get the result you need. But what line filters do you need? And how do they all work? Find out everything you need to know here.

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What is an air line filter?

A compressed air filter or air line filter is used to filter impurities from atmospheric air, like dust, oil and moisture, to make compressed air viable for use.

Just like air dryers, they are a crucial part of the air treatment process to make sure your compressed air is clean and safe to use, and to increase your equipment’s life span.

How do compressed air filters work?

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The working principle of compressed air filters changes depending on the type of air filter you use. 

The most common air line filters and their basic working principles:

  • Particulate air filters remove dust and other particulates from the air after compression by catching and retaining them within the air compressor. They are often combined with an adsorption air dryer. 
  • Activated carbon air filters remove gases and odours from the air with a composite carbon medium. These filters are often used in the food industry and for breathing gas.
  • Coalescing air filters filter oil and water particles from the air and condense them into an easily expelled mass. Contrary to moisture separators, coalescing air filters only remove moisture and oil aerosols, not actual liquid.
  • Compressed intake air filters remove microscopic contaminants from the air, as well as possible chemical particles.

What compressed air filter types are there?

  1. Particulate air filters
  2. Activated carbon air filters
  3. Coalescing air filters

1. Particulate air filters

Particulate air line filters remove dust and other harmful particles from compressed air. Like the membrane air dryer, the particulate filter uses a membrane that only lets air pass through and blocks other contaminants like dust, pollen and dirt.

Why choose a particulate air filter?

Particulate air filters are often used after an adsorption dryer like a desiccant dryer. They also filter internal particulate matter like corrosion to help your air compressor live longer.

Benefits of a particulate filter

  • Filter particulate impurities like dust
  • Prevents clogs in air lines

If you’re looking for a finer filter that removes fumes and vapours, the activated carbon filter is what you need, for moisture you are better off with a coalescent filter.

2. Activated carbon air filters

Activated carbon filters are often referred to as vapour removal filters, perfectly describing how carbon is used to attract gaseous contaminants and immobilise them. The carbon has a large surface area making it a durable type of filter.

As the filter becomes more saturated, however, the pressure will need to drop to reach the same quality of filtration. In order to maintain a reasonable amount of pressure, the carbon filter needs to be replaced every so often.

Why choose an activated carbon air filter?

Activated carbon filters or vapour filters are mostly used for food processing and the production of breathable air.

Reasons to go for a vapour removal filte

  • Filters gaseous contaminants like odours, chemical fumes and vapours
  • Most common filter type
  • Easy to maintain

Vapour filters are often followed by a particulate filter to catch possible carbon particles that break off into the air.

If you’re looking for a filter to take care of moisture, you are more likely to find what you need in a coalescing filter.

3. Coalescing air filters

Coalescing air filters remove liquids like water, aerosols, lubricants and other oil particles from the air. They coalesce aerosols into droplets through pressure drops and the tortuous path working principle.

Because of this versatile way of working, coalescing air filters also catch particulates. They are caught along with the aerosol particles, drained and run through an oil-water separator to avoid pollution.

As with the carbon air filters, coalescing filters need regular replacing to avoid the pressure dropping too dramatically.

Why choose a coalescing air filter?

Coalescing air filters are incredibly versatile, though not very energy efficient.

  • Filter water and oil aerosols
  • Filter particulate contaminants to a high degree


How do I choose the right compressed air filter?

Choosing the right compressed air filter is an important step when optimising your air treatment system. With these tips, you’re on your way to choosing the perfect compressed air filter.

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  • Find out what type of filter best fits your goals. An auto shop will need a different quality of compressed air than a food processing business.
  • Pick the filter type you need without going overboard. Filtering the air more than you need to will not make a difference for your work, but will cost you more.
  • Finally, make sure to calculate the costs in the long run. Cheaper compressed air systems might cost less now, but you’ll end up paying a lot more in repairs, new material and replacements over the years.

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Get expert advice

Not sure what type your air line filter is or how to make sure you choose the right one? Then get advice from the experts at Mark to make sure you make the right choice or get a quote.

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