Moisture (Water Vapor) Compressed Air Test Results

Moisture (Water Vapor) Test Results Greater Than 3900 ppm or

Ambient Pressure Dew Point Greater Than 22 Degrees F Discussion


The TRI method for conducting Compressed Air Moisture Testing is an  on-site method that directly measures the moisture content of the compressed air stream using a color indicator TRIAirTesting_Cylinders3tube. We choose to use this onsite method because moisture content measured from a low-pressure sample container can be wrong due to the loss or gain of moisture through interaction with the interior surfaces of the sample container including the polymeric and elastomeric seal. Also, differences between the sampling temperature and the temperature when the moisture analysis is conducted remotely can introduce error into moisture results.


When moisture (water vapor) compressed air  test results on the analytical report show values of >3900 ppm or >22° F this means that the air being tested has more moisture than the TRI Air Testing methodology is able to measure. Typically this means that the compressed air system has no functioning equipment for lowering the water vapor level. The air in the compressed air system lines when exiting the compressor is probably saturated with water vapor and liquid water will be condensing. The condensed liquid water will then be exhausted to the room through a liquid collection/purge system. The compressed air is still saturated with water vapor and when cooled, such as entering an air conditioned building, more liquid water will condense in the piping system. The concerns of high moisture as water vapor and especially as liquid water are that they can promote corrosion and microbiological
growth in the piping system.

There are three main types of  compressed air system dryer methods for lowering the amount of water vapor in the air; a refrigerated dryer, a desiccant dryer or a membrane dryer. A refrigerated dryer is capable drying the air to at least -5° F ambient pressure dew point or 973 ppm. A desiccant dryer is capable of drying the air to at least -50 ° F ambient pressure dew point or 67 ppm. A membrane dryer is capable of drying the air to at least -40 ° F ambient pressure dew point or 127 ppm.

More information here from Kaeser on the Art of Dryer Sizing. Compressed air dryers are commonly rated to achieve a specific moisture level (e.g. 40°F pressure dew point) for a certain volume of air flow (cfm).

For more information about compressed air and compressed air testing, visit


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