As a rule compressed air is cleaned through a combination of different filters (from coarse to fine). In this manner, the service life of the individual filters is noticeably increased. The first filter stage is normally a cyclone separator or prefilter, which removes the coarse dirt and water drops. This is followed by a microfilter or sub-microfilter, which also filters out oil and water aerosols. In order to also remove oil vapours from the compressed air for special applications, an activated carbon filter can be attached downstream to the sub-microfilter. Which filter combination is used at which point depends on the requirements of the application.