You must run a filter between your compressor and your airgun

If you are into precharged pneumatic (PCP) airguns and have bought a compressor – you need to also make sure you have a good inline filter. The reason is pretty simple, any compressor sucks in everything that is in the air including dust and moisture. You may not have stopped and though about it, but there are also impurities the are bonded to the water as well – sulfurs, acids, minerals, etc. You really need to filter the air before you pump it into your airgun or air cylinder.

If you are wondering why this is critical it is because your airguns use precise maching and a ton of O-rings. You don’t want contaminants to be introduced that cause premature wear or corrision of the aluminum surfaces. The cleaner your air supply is, all things being equal, the more reliable your airgun will be and the less maintenance required. Please note I am not saying this will make your o-rings and what not last forever – all airguns will require maintenance at some point and the most common need is to go though and replace the seals. Clean air will help them last longer than dirty air is all I am saying.

“But isn’t the oil & water separator in my air compressor enough?” is often asked and the answer is a resounding “No, it is not”. High pressure air is hot and as it expands and cools, condensation forms and this continues after the separator. Yes, the separator is better than nothing but it is not sufficient. What you need is a long filter made up of multiple elements.

Buying a Filter

First off, and I can’t stress this enough, you need a filter with a working pressure equal to or greater than your compressor. A high-pressure air (HPA) compressor has working pressures between 4-5,000 PSI these days so your filter must as well and they are specialized – these are not shop air compressors working at 150-250 PSI. One of those would explode.

Second, you need a long filter. When you go to Amazon or other sites you will notice there are short stubby filters that are 1.5-2.0″ long. I sometimes use them from the tank to the gun but I would not recommend them as the filter immediately after the compressor. They are better than nothing but they are too short and usually just have mesh or foam filter elements inside – no dessicant or carbon.

The ones I would recommend are 11.8″ (300mm) long and outside diameter of 1.9″ (50mm) at least. These filters tend to use replaceable cartridges that contain a mesh for particulants, a dessicant for drying the air and a carbon section for neutralizing chemicals that remain.

Air enters at the dessicant end (the white section) and moves towards the black carbon and out the end. There are mesh wafers at the ends and between the dessicant and carbon to trap particulants. The end caps of the filter unscrew and this cartridge can be pushed out and replaced with a new one as it becomes more and more discolored. If airflow stops or you notice fill times taking longer and longer, a plugged filter cartridge is your most likely culprit.
This is my GX CS4 compressor and I am using the factory airline and its 8mm quick connect female fitting to connect to the filter’s male plug. The filter I am currently using and really like is sold on Amazon by “FASTTOBUY”. It’s very well made and you can buy additional filter cartridges. The brass colored nut you see on the surface of the left side’s end cap is the burst disc. A burst disc is designed to break first and let air leak vs. allowing the filter to exceed its safe operating pressure. From the filter, there is a Manloney brand air hose with an 8mm plug on one end and an extended length female fitting on the other.

If you read the captions, I really like my 300mmx50mm FASTTOBUY filter. It’s long enough for a fair amount of drying and cleaning to happen but also ins’t completely unwieldy either as I need to move my compressor around. I have toyed with running two filters in series as a first stage and a second stage and may try that some day but for now, I just run the one.


I can supply clean dry air to my PCP airguns at home with this set up. The FASTOBUY unit works and the fittings they used have worked with what I have so far. They also provide some spare parts including another filter cartridge.

Do you have to go with the one I am recommending? No, of course not. Just look for a long one that gets good reviews and you can get spare filter cartridges for.

What I am telliing you very directly is NOT to fill your airguns right off the air hose direct from the compressor. You need a filter to get rid of water and other contaminants before you fill your airgun or air cylinder.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

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