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Filtering Compressed Air for Use in Painting – A Complete Guide

When it comes to using an air compressor to provide air for a spray gun one of the critical things to consider to ensure you get a quality finish is to ensure your compressed air is clean and dry. If your compressed air has water in it that can create problems like solvent pops in your paint or if you have oil in your compressed air line it can create issues like fish eyes, both of which are problematic as they will impact the product finish you achieve. To deal with these issues it is critical to ensure you have proper compressed air filtration for your painting process. There are a few different degrees of compressed air filtration that you can implement which we will cover further so that you can decide what kind of compressed air filtration is right for your painting process needs.

Air Filtration at the Compressor

The first option for filtration of compressed air is directly at the air compressor.  Air compressors can have air filtration built in with options like a desiccant bead or refrigerant dryers. Both help remove moisture from your compressed air but have unique pros and cons associated with each of them.

Refrigerant dryers offer a better initial cost compared to air compressor desiccant dryers. They are also not damaged by oil in your air stream which can be a benefit with older compressors that may pass oil with the operation. The primary disadvantages to refrigerant dryers include that they do not cool the compressed air as much which means they do not remove as much moisture from your compressed air.

Alternatively, there are regenerative desiccant dryers that can be incorporated at the compressor which bring compressed air temperature lower than refrigerant dryers. What this offers practically is an increase in the amount of moisture that is drawn out of your compressed air line. The main disadvantages to a desiccant air dryer at the compressor is that they have higher initial and operating costs. They also have a bit more maintenance to consider because if desiccant comes in contact with oil it can become coated and become ineffective at removing moisture from compressed air which will require you to replace the desiccant beads.

Air Piping Considerations

So the first stage of filtering compressed air for painting occurs at the compressor. The second aspect of filtering compressed air for painting to consider is the size and way you run piping for your compressed air in your paint shop. The two critical things to remember about piping for an air compressor include ensuring you select a large diameter pipe and that you utilize what is known as air drops. Airdrop legs are pipe that comes off your compressed air line and goes beyond where you will actually have connections for compressed air. At the bottom of your drop leg should be a way to drain moisture as the leg will allow for an additional point for moisture in your compressed air line to settle out. When it comes to selecting compressed air line pipe diameter you always to use at least a ¾” pipe but the larger pipe you use the less air volume and pressure you will lose.

Air Filtration Prior to Your Paint Equipment

After you have properly filtered your compressed air at the compressor and implemented proper piping for your compressed air the final level of compressed air filtration will occur adjacent to the drop leg from your compressed air line.  This is where you will add an additional or in some cases only air filtration option.  Air filtration options for compressed air lines prior to a tool, like a paint spray gun, are offered in one, two, or three stage designs. A single stage air filtration unit offers an oil water extractor. An oil water extractor removes oil and water down to .05 microns by a tornado like spinning of the compressed air within the unit.  After a basic oil water extractor the next stage ads a coalescent filter which removes contaminants like oil and water down to .01 microns. While the final stage adds desiccant beads which remove water vapor making desiccant beads the most pure filtration of compressed air. You can often times by these stages one at a time which can help keep initial costs down and can allow you to expand your compressed air filtration to be better over time. Typically for almost all paint applications at the very least, you will use a two stage air filtration unit.  If you find you are still having issues with problems like solvent pops and moisture bubbles you can then consider adding the desiccant bead dryer if needed or go with a complete three stage compressed air filtration unit.

Final Thoughts

Ultimately properly filtering your compressed air for painting along with strong painting technique will ensure you achieve quality finishes in your painting projects. Remember that you should consider air filtration at the compressor, proper design of your compressed air lines (both size and layout), as well as compressed air filtration right before your tool that uses compressed air. By considering these steps you can ensure that you get the best results. If you are looking to learn more about compressors you can check out this site for resources on portable air compressors and more.

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