Ask the Expert Question-and-Answer Archive

by Ron Joseph

January, 2002

Compressed Air For Painting Operations

Q. Hi, hopefully you can help me since no one else can. I have emailed perhaps ten different paint manufactures this same very question and they have never responded. However, the problem is that I am looking for properties of compressed air such as temperature, moisture content, relative humidity - what do these properties need to be so that when mixed with the paint the paint atomizes correctly and you receive a good paint job. I need a set of standards such as ISO or ANSI or other published data to support my mechanical design project. I would appreciate your help. Thank you very much.

A. I'm not an expert in compressed air, but in our industry we generally prefer the air to be at ambient temperature, usually between 60 - 75 °F, although there are no standards on this.

The compressor should be followed by a dehumidifier and more often than not it is a refrigerated dryer. I believe that the dryer removes moisture at approximately 34oF. You should contact people like Ingersol Rand who sell both the compressors and dryers. They will also provide you with you with temp/RH charts that will be helpful. You might find these on their websites.

The humidity of the compressed air at the spray gun should be "dry". But here "dry" simply means that we don't want any condensate in the compressed air piping. There are no standards that I'm aware of concerning the RH of the air that is fed to the spray gun. The dryer the better.

Assuming that dryer does not eliminate the moisture adequately, it is common practice to add a drain plug at a low point in the piping so that at the beginning of a working shift the painters can easily drain any liquid water that has collected. Alternatively, you can purchase oil/moisture separators (filters) that are installed in the spray booth adjacent to the point at which the compressed air is fed to the spray gun.

ITW-Finishing Systems, Fluid Air Products, etc., sell regulators and filters for the painting industry, and you can get more info from their websites.

Somehow I doubt that you will find ANSI or ISO standards on this topic, but if you do, please send me the information so that I can include it on my website