All compressed air contains a certain amount of moisture in the form of water vapour. The volume of water vapour that the air may contain, however, is limited, and if the moisture content is greater than this limit, the excess moisture precipitates as condensation. The maximum amount of water vapour that the air may contain drops at lower temperatures and at increasing pressure, respectively, calculated per volume unit of air.

A mechanical water separator, such as VAM 05 A, only separates free water and should therefore be placed where the compressed air is as cold as possible, in other words, as far away from the compressor as practically possible, but where temp is slightly above 0°C