Compressor Air Filter

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The compressor air filter  is one of the air compressor components that may come with your air compressor, but unfortunately, does not usually come with the lower cost, DIY type air compressors purchased through retail outlets.

What are compressor air filters, how and where are they installed, and what can be done when they don’t work properly?

Before we zero in on the nuts and bolts of compressor air filter itself, a typical one of which is shown in the image below, we would like to explain why an air filter is a piece of equipment you would want to install on your air compressor if it did not come with one.

Compressed air filter
Typical big box store type of compressor air filter

Compressed air is hot and wet!

The air compressors job is to cram air into the compressor tank.

To do that it pulls air in from around the intake of the compressor, then the compressor pump drives that air into the tank,  forcing more and more air into the smaller area.

The compressor pump gets hot from the friction of operation and from driving the air into the tank this heats up the compressed air in the tank.

As the compressor pumps air into the tank, that volume of air is reduced which increases the pressure in the tank. This is desirable. What is not desireable is that the air now in the compressor tank still has the same amount of moisture vapor in it as it did when out in the atmosphere, and this dramatically increases the humidity level in the compressor tank.

The humidity inside the tank continues to rise as the compressor pumps into it.  It won’t be long before that hot air inside the compressor tank is holding all the water it can. Once the humidity level passes the 100% level inside the tank – sometimes within minutes depending on the tank size – free water is generated in the tank as the water vapor in the air turns back into free water.

When the compressor stops, the air in the tank starts to cool. Cooling air can hold less moisture vapor, so as the compressed air chills down, even more water is released into the tank.

Then you turn on your air tool. Compressed air laden with a high level of water vapor and containing some free water from the bottom of the tank rushes down your air line to your air tool. As the air moves along the hose, it cools further, and even more water vaport condenses into free flowing water in your air hose.

Sometimes you can even see water dripping from the exhaust vent of an air tool if it has been used for a long enough duration.

Water is not good for most compressed air using applications.

How do you try to stop the water? Enter the compressor air filter.

Compressor Air Filter

Compressor air filter
Partially disassembled air compressor air filter

The image just above is of a general purpose compressor air filter.

This air filter comes with a bowl guard, shown on the left.The bowl guard is part of this filter assembly as the filter bowl itself is made of polycarbonate (plastic). Over time, the plastic bowl may be affected by corrosive material coming down the air line, the plastic itself deteriorates over time, there may be a slight defect in the bowl itself, and the external metal guard is there in case the plastic bowl shatters from the internal air pressure. It’s a safety device. It is, in our opinion, not an option for any compressor air filter that has a polycarbonate bowl. If your compressor air filter has a plastic bowl, it should have a metal bowl guard.

Removing the compressor air filter bowl guard

This bowl guard is attached to the filter head by a bayonet-type connection. This type of connection is quite simple to operate.

Compressor air filter bowl guard
This compressor air filter bowl guard is attached with a bayonet-type mount.

When it is required to remove this compressor air filter bowl guard, for example, you wish to change the filter element, if you grasp the guard, pull down slightly on the slide shown in the photo above, push up on the bowl – rotate it – and then gently pull down and the bowl guard will release from the housing. This exposes the polycarbonate bowl.

Other types of polycarbonate bowl guards may thread into the compressor air filter housing. If your compressor air filter has no obvious slaiding latch mechanism on the side, then likely it will be threaded on. Turn that bowl guard in a counter-clockwise direction to unthread it.

Inside the compressor air filter

After you have removed the bowl guard, you can then typically remove the polycarbonate bowl, making the inner components of the compressor air filter accessible.

There is more on the inner components of the compressor air filter and what those components do right here.

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