The FRL (Filter Regulator Lubricator) assemblies are examples of such air treatment systems. The FRL unit consists of a filter which filters the air and removes particulate matter and dust. The Regulator reduces the air pressure to the desired value while the Lubricator delivers a fine aerosolised spray of oil to the air.
The oil spray in the air may be desired for certain pneumatic tools such as drills and air motors. The oil serves to lubricate the parts in these equipments.