In-line filters or as they are also known compressed air filters are used in addition to existing air treatment in your system and provides extra filtration. These can vary from 5 micron rating down to 0.01 micron and also activated carbon filters.
This filter element inside the filter housing removes liquid and debris from your compressed air and therefore allows compressed air to be used in many applications including spraying, manufacturing processes and with the correct range of inline filters even breathing air application.