Compressed air filters

Compressed air filters protect your equipment from dust, dirt, oil and water. Dust will wear down your equipment (like the air motor in grinders, pneumatic actuators and it can make pneumatic control valves get stuck.

Especially when the dirt and dust is combined with oil (which is often the case with compressors), a sticky mess can form inside valves, motors and other compressed air equipment.To protect your equipment, you need to install some compressed air filters. Which ones? Find out below… There are many different kinds of filters, and I have often seen people using the wrong one.

I have seen many ‘compressed air filter mistakes’ for that matter, like: wrong filters installed, too small filters installed, filters installed in the wrong place.

People also tend to forget about their filters… while the compressor gets its service every year, people seem to think that their filters will last a lifetime!

That’s not true of course… and it will cost you money!

Filter buildup

Look at the picture below what a typical filter looks like.

The workings are quite simple: air enters on one side and goes through the filter element, where all dust, water or oil is collected. The clean air then leaves the filter housing on the other side.

As you can see above, the compressed air filter usually is made up of two main parts: the housing and the filter element.

The filter element itself is the part that is doing the job: filtering your compressed air.

In some cases, the filter housing is doing an important job too: it’s often used to separate dust or water/oil droplets by cyclone action. What does it mean? The housing is designed in such a way that the compressed air moves around in it like in a tornado. All the solid particles and droplets will get smashed into the walls of the housing, while the rest of the air moves to the filter element.

You can buy the filter elements separately from the housing, so you can change them for new ones every year or so.

Be careful when buying your filter housings: what kind of filter elements can they hold? If you like to change filter type later on, do you need a new housing also?

Also, check the maximum flow rate. If you’re thinking about buying extra compressors or a bigger one in the near future, it might be a good idea to over-size your air filters so you don’t have to buy new ones in the future.

Filter types

There are many different types of compressed air filters.

So you need a compressed air filter, but are overwhelmed by all the different types, sizes and specifications.

Don’t worry! Let me help you..

Particulate filters

Particulate compressed air filters are used to remove dust and particles from the air.

They use different methods to do this, but the main thing is that the dust particles get trapped in the filter material and stay there.

The dust is ‘stored’ inside the filter material. But it is designed to do this and therefor has a large dus-holding capacity.

But, when the filters becomes ‘full’, the pressure drop increases and the amount of dust particles that make it past the filter also increases.

So every so many months, the filter element needs to be replaced.

Coalescing filters

Coalescing filters are used mainly to capture oil and/or moisture that is suspended in the compressed air in very tiny droplets.

Unlike particulate filters, they don’t trap the contaminations in the filter material.

The working principle is different: the filter material makes the small water and oil drops and mist stick together to form larger drops.

The drops then fall down to the bottom of the filter. A drain is fitted to remove the liquid from the filter housing.

If the air is free of solid particles, the coalescing filter can theoretically work ‘forever’. However, there are always solid particles present in the compressed air. These get stuck in the filter material, slowly blocking the air flow.

For this reason, the coalescing filter also needs to be replaced every so many months.

Activated carbon filters

Activated carbon filters remove (oil) odors and vapors.

They are not very common in ‘shop air’ installations or in industrial installations for that matter. They are mostly used in factories where food or medicine is produced or for breathing-air applications.

Unlike other filters, these activated carbon filters don’t filter out any solid or liquid contaminations. In fact, the air should be totally free of all solid and liquid contaminations before passing through an activated carbon filter!

Costs and considerations

When shopping for compressed air filters, keep in mind that quality is important.

Quality air filters will produce cleaner air, which means fewer problems with your equipment.

Quality air filters have a lower pressure-drop then low-quality ones. This will save you energy. Every pressure drop in your system (from filters, dryers, long piping etc.) will require you to put your compressor on a higher setpoint, which will cost you extra electricity.

Over time, dust will accumulate in your filters. All this dust will cause an extra obstacle for the compressed air. This means the pressure drop over your filter will become higher over time.

Low-quality air filters will clog up quicker than quality air filters. This means that you’ll have to buy new filters more often. But it also means that the pressure drop over your filter will become higher, quicker, with low-cost air filters.