When compressed air is expanded through a spray gun, the air cools down and the vapor condenses into a liquid. The bulk liquids created by the expansion of compressed air through an orifice or a control valve can lead to major problems. As an example, when it mixes with paint in a spray gun it ruins the paint job. In the case of blast media it creates clogs in hoses and nozzles.
Humidity and Water Vapours
Water vapor is the gaseous form of water. The higher the temperature of the compressed air, the more water vapor it can contain. As a rule of thumb, every 20 degrees of temperature increase approximately doubles the moisture content of your compressed air.
Water and Bulk Liquids
When the hot saturated compressed air cools down, the water vapor condenses into liquid water. Condensed liquid water leads to water aerosol, an emulsification of water and air.
Dirt and Solid Particulates
The dirt category of contaminants includes pipe scale, rust and solid particulates. These contaminants are often the result of the presence of water and humidity in the compressed air and have a negative effect in surface preparation and paint jobs.
Oil and Aerosols
Oil contaminants can enter the compressed air atmospherically or from the compression systems themselves (lubrication, cooling, and sealing). Oil can lead to fish eyes.