Compressed air is essential for many UK businesses, but it is rarely clean when it enters the system. There are millions of tiny particles in the air around us, and when these contaminants are compressed, they become more concentrated, which can damage equipment and ruin products.
It’s not just the physics that facility managers need to know about particulate filtration, it’s also about how to keep everything working and the energy costs low. This guide goes over what these filters take out, how they work, and why it’s important to pick the right one for your business.
What Are Particulate Filters in Compressed Air Systems?
What Do These Filters Actually Remove?
Particulate filters are the main way to keep solid things out of your compressed air, and there are four main places these pollutants come from:
- Ambient Air: Dust, pollen, and soot drawn into the compressor.
- The Compressor: Small metal or plastic fragments from internal wear.
- The Piping: Rust and scale that flake off inside the pipes.
- Desiccant Dust: Fine dust created by adsorption dryers.
A particulate filter is a must if you use desiccant dryers. Over time, the drying beads break down and create dust that needs to be caught before it gets into your production lines.
How Do They Trap Such Small Particles?
A filter is like a sieve, but more advanced. Simple straining only stops big pieces of debris, so high-efficiency filters use four different ways to catch even tiny particles:
- Straining: Blocking larger particles physically.
- Impaction: Heavy particles hit the filter fibres and stick.
- Interception: Particles pass close to a fibre and are grabbed.
- Diffusion: Tiny particles move erratically, making them likely to hit a fibre eventually.
The hardest particle size to remove is used to test the filters, which makes sure they work the same way every time, even in tough conditions.
Particulate vs. Coalescing Filters: What is the Difference?
Why Flow Direction Matters
There is a big difference between wet coalescing filters and dry particulate filters, and a lot of system problems are caused by using them incorrectly.
- Dry Particulate Filters (e.g., DDp/PDp): Air flows from Outside-to-Inside. This uses the larger outer surface to catch more dust, lasting longer.
- Coalescing Filters (e.g., DD/PD): Air flows from Inside-to-Outside. This allows liquid droplets to merge and drain away.
Where Does Each Filter Go?
In a complete system, the order of filter placement is important. Here is a simple layout:
- Coalescing Filter: Placed before the dryer to remove oil and water aerosols.
- The Dryer: Removes water vapour.
- Particulate Filter: Placed after the dryer to catch any dust.
- Carbon Filter: Placed last to remove vapours (if needed).
The Risks of Poor Filtration
How Contamination Affects Your Equipment
When dust mixes with oil residue, it forms a sticky sludge which can coat the valves in your pneumatic systems. In practice, this causes “stiction”, where a valve that should move instantly might lag or get stuck, and on an automated production line, this timing error can lead to jams and unplanned stops.
What Happens if Drains Fail?
Coalescing filters rely on a drain to remove collected liquid, but if this drain blocks, the filter housing fills with water. Eventually, the airflow will push this water back into the pipes, bypassing the filter entirely and potentially flooding the downstream equipment.
Avoiding Filter Failure
If a filter is left too long, the pressure difference across it becomes too high and, in extreme cases, the filter element can collapse. This releases the trapped debris into the system, causing major quality issues. Regular filter changes prevent this risk.
The Cost of Clogged Filters
How Pressure Drop Wastes Energy
Every filter resists airflow. Even new filters have a small “pressure drop” and as filters catch dirt, this resistance grows even more. The compressor has to work harder to push air through a blocked filter, and a pressure drop of just 1 bar increases energy use by about 7%.
For a standard 75 kW compressor, an unnecessary 0.5 bar drop could waste over £3,000 a year in electricity. Changing filters is often cheaper than paying the extra energy bill.
When Should You Change Them?
Filters don’t block up steadily. They stay clear for a long time, then clog rapidly once they reach near-capacity.
If you wait for the gauge to hit the red zone, you will have already been wasting energy for weeks. A fixed replacement schedule based on running hours is usually the most economical approach. For more on these costs, read our guide on the Importance of Compressed Air Quality & Filters.
Atlas Copco Filter Solutions
Dry Dust Filters (DDp/PDp)
These are designed specifically for dry contaminants and are usually found after desiccant dryers.
- DDp: Catches particles down to 1 micron.
- PDp: Catches particles down to 0.01 micron.
- Remember, these must be installed with Outside-to-Inside flow.
Coalescing Filters (DD/PD)
These remove aerosols and are placed before dryers.
- DD: General-purpose protection.
- PD: High-efficiency polishing.
- Always place a DD filter before a PD filter to protect it.
The UD+ Series: A 2-in-1 Solution
The UD+ series uses “Nautilus” technology, where the media is wrapped in a spiral to save space and improve flow.
- Combined Performance: One UD+ filter does the job of both a DD and PD.
- Energy Savings: It offers a 40% lower pressure drop than using two separate filters.
- Easy Maintenance: The inPASS system allows you to change the element without stopping the air supply.
Specialised Options
- QDT (Carbon): For removing oil vapours and odours.
- SFA (Silicone-Free): Essential for automotive paint shops to prevent finish defects.
You can view the full range on our Atlas Copco Compressed Air Filters page.
Staying Compliant with UK Regulatory Standards
ISO 8573-1:2010
This standard is the benchmark for air purity and classifies air based on solids, water, and oil.
- Class 1: Required for sensitive electronics.
- Class 2: Common for general manufacturing and food contact.
Industry Requirements
Different sectors have specific rules to follow:
- Food & Beverage: Follows BCAS guidelines. Air touching food generally needs Class 2:2:1 purity.
- Medical: HTM 02-01 requires “duplex” systems. This means having a backup filter bank so the supply is never lost during maintenance.
- Safety (PSSR 2000): Large filter housings are pressure vessels and must be inspected regularly to meet safety laws.
See our Guide to Compressed Air Compliance for more details.
Maintenance Tips
Stick to a Schedule
Depending on the model, we suggest changing parts every 4,000 to 8,000 hours. Also, do not ignore the drains, because mechanical drains often get stuck. Upgrading to electronic “zero-loss” drains is a smart move that improves reliability and saves compressed air.
Test Your Air Quality
The first thing to do is to put in the filters and test that they are working. Regular checks of the air quality will make sure that it meets standards like ISO 8573-1 and that there are no leaks around the edges.
Summary of Operational Value
A healthy air system needs particulate filters to keep your equipment from getting worn out and to make sure your products stay clean.
You can avoid problems like valve failure and high energy bills by knowing the difference between dry and coalescing filters and keeping up with maintenance.
Schedule Your System Audit
Is your system working well? J Ll Leach has depots in Stoke-on-Trent, Birmingham, and Shrewsbury. We can help with installation, maintenance, and air quality testing all over the country.
Call us today to talk about upgrading your filters or to schedule a compliance audit for your building.