How Particulate Filters Work in Air Compressor Systems

Across Scotland, a lot of industrial businesses rely on compressed air to keep their operations running.

It runs everything from packaging lines in the Central Belt to factories in the Highlands. But the air around us isn’t clean enough for these sensitive processes on its own. It often has dust, oil aerosols, and moisture in it that can damage your equipment.

Particulate filters are usually needed to remove solids, and coalescing filters are needed to remove aerosols. This guide was put together by Design Air (Scotland) Ltd to help you understand how these filters work and how to take care of them.

How Do Particulate Filters Work?

It helps to think of compressed air filters as more than a simple screen.

A sieve only stops particles that are larger than its openings. A high-efficiency particulate filter works differently – it’s designed to capture contaminants that are far smaller than the gaps between the fibres themselves.

The filter media employs four primary physical techniques to accomplish this:

• Straining: This is the simplest mechanism at work. It behaves much like a sieve – particles that are larger than the gaps in the filter media are physically blocked and held back.
• Inertial Impaction: This comes into play with slightly heavier particles, typically in the 0.3 to 1 micron range. Because of their mass, they can’t follow sudden changes in airflow. Instead, they keep moving straight ahead, hit a filter fibre, and stick there.
• Direct Interception: This mechanism deals with lighter particles, typically around 0.1 to 1 micron. They follow the airflow through the filter, but pass close enough to a fibre to brush against it and adhere.
• Diffusion: This applies to extremely fine particles, below about 0.1 micron. At that scale, constant collisions with gas molecules push the particles into a random, wandering motion. That randomness increases the chance they’ll collide with a filter fibre and be captured.

Where Do Contaminants Come From?

In systems, filters are usually used to control three main sources of pollution:

1. The Atmosphere: The ambient air that your compressor draws in naturally contains moisture, dust, and pollen.
2. The Compressor: Small wear particles may be released during the compression process itself. Additionally, oil aerosols may be introduced into the air stream by oil-lubricated compressors.
3. The Piping: Older pipe systems can sometimes develop rust or scale. Upgrading to modern aluminium compressed air pipework is a good way to reduce this issue.

Dry and coalescing filters are built for different jobs – which is why the distinction matters.

Dry Particulate Filters

Dry particulate filters are used to deal with solid, dry contamination – things like dust, scale, or rust. 

To do that efficiently, they tend to use a pleated filter element – increasing the surface area available for particles to collect.

• Flow Direction: Air enters from the outside of the element and flows inward. That direction isn’t accidental. It keeps the dirt on the outer face of the media, where there’s more room for it to build up without restricting flow too quickly.
• Why: What they don’t do is handle liquids. Oil and water will pass straight through, which is why dry particulate filters are normally paired with other stages when moisture or oil is a concern.

Coalescing Filters

These are used to remove liquid aerosols (oil and water) as well as solids. They usually use a deep bed of glass fibres.

• Flow Direction: Flow direction matters with coalescing filters. Air is designed to pass from the inside of the element to the outside.
• Why: As the air moves through the media, fine oil or water droplets are forced together into larger drops. Once they’re heavy enough, gravity takes over and pulls them down to the drain at the bottom of the housing.
• Important Note: If the filter is installed the wrong way around, that process breaks down. The liquid can’t drain as intended and may be carried back into the airflow instead of being removed.

How Does Atlas Copco Filter Technology Work?

At Design Air, we supply Atlas Copco filters which are designed to meet specific air quality needs.

• DD Series: This is a general-purpose coalescing filter. It removes solids and oil aerosols to a standard suitable for general industrial use.
• PD Series: This is a high-efficiency filter. It is designed to polish the air, removing very fine particles and aerosols.
• DDp / PDp Series: These are the dry particulate versions, designed specifically for dust removal.
• UD+ Series: This is a 2-in-1 solution. It combines the functions of two filters into one unit. It uses a spiral design to improve airflow and reduce energy loss. You can see the specifications for the Atlas Copco UD combination filter on our product page.
• QD Series: These use activated carbon to remove oil vapours and odours. They are typically used where air quality is critical.

Where Should You Place Your Filters?

Getting good results isn’t just about the filters themselves. 

The order they’re installed in matters too. A typical compressed air system follows a set sequence to keep each stage doing its job properly.

1. Air Compressor: The source of the air.
2. Wet Receiver: To collect bulk water.
3. DD Filter: To remove the majority of oil and dirt.
4. PD Filter: To clean the air further.
5. Air Dryer: To remove moisture. Note: It is best to place coalescing filters before the dryer to protect it from oil.
6. DDp / PDp Filter: To catch any dust that might come from the dryer itself.
7. Activated Carbon Filter: If you need to remove odours or remaining vapours.

How Do Filters Affect Energy Costs?

There is a small amount of resistance to the airflow in every filter. This is called pressure drop. Your compressor uses energy to push air through this barrier.

In general, a pressure drop of 1 bar increases energy use by about 7%.

When filters are new, this resistance is low. 

But the resistance increases as they trap dirt. As a filter blocks, the pressure drop rises – and energy costs rise with it.

In most cases, keeping to a regular replacement schedule is cheaper than paying for the extra power a clogged filter demands.

If energy use really matters, it’s worth looking beyond the filters as well. 

Air leaks elsewhere in the system quietly add to running costs, and a proper leak survey can uncover other areas where energy is being lost. 

Why Does Maintenance Matter?

Frequent maintenance aids in preventing typical operational problems. If filters are left on for too long, you may come across:

• Carryover: Contaminants may be able to get past the media and into your piping network if the filter is blocked.
• Filter Damage: High pressure can damage the filter element itself.
• Valve Issues: Dirt and oil can make pneumatic valves stick or work slowly.
• Product Issues: In clean environments, particulates can affect the quality of your final product.

How Do UK Regulations Affect Filtration?

For businesses in Scotland, following industry standards helps ensure safety and quality.

• ISO 8573-1: This standard groups air purity into classes. You can check your current levels with an ISO 8573 air quality test.
• BCAS Best Practice: For the food and beverage industry, guidelines suggest specific purity levels (Class 2:2:1) for air that touches food.
• HTM 02-01: This applies to medical air and requires backup filtration to ensure a continuous supply.
• PSSR 2000: Filter housings are often pressurised, so they should be included in your safety checks.

Which Industries Rely on Clean Air?

Many sectors in Scotland have specific needs when it comes to filtration:

• Food & Beverage: Clean air helps maintain hygiene standards.
• Manufacturing: Removing dust prevents machinery from jamming.
• Paint & Finishing: Fine filtration prevents blemishes in paint finishes.
• Pharmaceuticals: These environments often require very high purity. Regular breathing air testing is often used here alongside filtration checks to ensure safety.
• Electronics: Clean air protects sensitive components during assembly.

Conclusion

Particulate filters sit quietly in the background, but they have a real impact on how safe and reliable a compressed air system is.

Get the selection right, don’t let elements run past their useful life, and you reduce wear on equipment while keeping energy use under control. It’s not complicated – just easy to overlook.

Design Air (Scotland) Ltd offers local support to help you manage your system efficiently. 

We cover everything from proactive compressor service plans to advice on how to improve the air quality. 

Get in touch with us today – we’d be happy to talk about your filtration needs.