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What an Air Line Filter is and How it Works. The experts at Power Equipment Direct explain how air line filters work to protect and extend the life of your air compressor and pneumatic tools


Air Compressor Filters 101

What an Air Line Filter is and How it Works

Air Compressor
Product Expert
Air Compressor Filters 101

Air compressor filters are referred to as air line filters due to their installation in the compressed air line downstream from the compressor.

Air compressor line filters will help to prevent many problems with your equipment and systems, both short-term and long-term.

Without an air line filter; water, oil and crud can cause major damage to your pneumatic tools or equipment

Quality air compressor filtration will help extend the life of your tools and improve the quality of air being put out.

Your typical air compressor filter will consist of 8 main components.

1. Air Inlet

Air Line Filter Diagram
This is where the air enters the filters. As air enters, the internal cap forces it into a downward spiral to the filter bowl. Be sure to size the inlet appropriately for your unit. While it's possible to use a larger filter on a smaller line, you should never use a smaller filter on a larger line. Doing so will restrict the air flow and put added stress on the unit as a whole.

2. Filter Cap
The filter cap is the part mentioned above that directs the flow of air through the filter. An arrow on the outside of the filter indicates the optimal direction of air flow, and should not be installed backwards.

3. Air Path
In order for the air to be discharged from the filter, it must follow the air path. The air path consists of entering a cyclonic phase and passing through the filter element. it's then able to be discharged.

4. Filter Discharge
The filter discharge is the the orifice through which the air leaves the filter. The sizing of the discharge should match the inlet size. Again, don't under-size your filter or you'll be restricting air flow.

5. Filter Element
The filter element is the part that actually filters the air. The filter element catches particulates you wish to remove from the air. As the filter does its' job, it becomes clogged with those particulates.

Once the filter is clogged, it will need to be cleaned or replaced. If CFM (cubic feet per minute) decreases, it may be due to a clog in the filter element. Using too fine of a filter element can cause more frequent clogging.

6. Filter Bowl
The filter bowl makes up the largest visible part of the air compressor filter. It connects to the cap housing by either threading into it or twisting and locking into place.

The filter bowl houses the filter element and directs the air back upwards toward the filter discharge. They can be made of plastic with a metal shroud or they can be made entirely of metal.

7. Filter Quiet Zone
The filter quiet zone is a zone at the bottom of the filter bowl where contaminants, oil, and water collect. There is usually a horizontal barrier that hangs down from the bottom of the filter element.

That barrier breaks up the cyclonic incoming air to prevent the debris at the bottom from becoming re-intrained in the air.

8. Drain
Eventually, the water, oil, and debris in the bottom of the filter bowl must be drained. Some filters come with manual drains, requiring you to periodically remove the plug and drain the contents.

Other filters come with float-operated drains or electric auto drains. Failure to regularly open and drain the collected water and debris will cause the water to rise above the barrier and become re-entrained, If this happens, your filter element will become contaminated with excessive water, oil, and debris.

How to Pick the Perfect Air Line Filter

What's a Micron?
Air line filters are measured by the size of the particles they can catch. The particulates caught in air filters are very small, and so they're measured in microns (1 micron = one millionth of a meter).

For example: 5 micron filter elements filter particulates as small as 0.0002 inches. These are very fine filter elements and may need to have a general purpose filter element installed up-stream of them to catch larger particulates.

General purpose filter elements are typically 30-40 micron sized. These will catch particulates in the range of 0.0010 to 0.0016 inches. Using general purpose air compressor filtration prior to the very fine air compressor filtration will help to extend the life of your air compressor filters, reducing how frequently you have to replace them.

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