The air compressor inlet filter: more important than you think

For today’s post in the ‘part of the day’  series, I want to talk about the inlet filter of your rotary screw air compressor.

The air compressor inlet filter protects your compressor from outside dust and dirt. This is important, because all the dust that is sucked in by the air compressor eventually ends up in the:

  • Oil

    XAS 87 inlet filter and housing
    XAS 87 inlet filter and housing
  • Oil filter
  • Oil separator

That’s really a bad thing, because it will deteriorate your compressors performance, increase the maintenance costs, lower the lifetime of the compressor element en increase your energy bill.

Dirt and dust in the oil can damage the bearings or the screw elements of a rotary screw compressor. The screw element is the heart of the compressor and is the single most expensive part of your compressor.

It is true that most dust will be filtered out by the air compressor oil filter, but what happens when the oil filter become clogged with dirt? Did you know the oil filters have an internal by-pas valve. Once the pressure difference over the oil filter becomes too big, the by-pass valve opens, sending unfiltered oil to the screw element and the bearings. The thought behind this is ‘better dirty or than no oil’.

Not only the oil filter will be clogged with dirt, also the oil separator. As a result, the pressure drop over the oil separator will rise. A clogged oil separator is bad for various reasons:

  • An increased pressure drop over the oil separator will decrease compressor output and increase energy costs.
  • An increased pressure drop over the oil separator increases the chance of an separator collapse. Trust me, you don’t want that to happen

As you can see… it’s very important to have high quality inlet filters on your air compressors. Clean them frequently and change them often.

Filter process

Did you know that the air filter only filters out 20% of the dirt?

The other 80% was already filtered out by the filter housing!

The process of removing dust from the intake air is a two step process. The inlet filter housing is constructed in such a way that you get an ‘cyclone action’ (much like the Dyson vacuum cleaners). This removes 80% of the dust. The remaining 20% is filtered out by the second step: the air filter.


Air compressor inlet filter housing
Air compressor inlet filter housing






My name is Cas. I’ve worked in the compressed air business for years and saw the same mistakes over and over again. This website is my answer. The best way to get started is to download my free e-book “Hidden Compressor Problems”.

Articles in 'Stationary Air Compressors'

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