3. FRL packaging units

3.1 Function and classification

The quality of compressed air in a plant depends on its purity, which is determined by the quantity of solid, liquid or gaseous particles present in the air. The international standard ISO 8573 classifies the quality of compressed air for general use. This quality is indicated by a three-digit number: the first refers to solid particles, the second to the hygrometric level, and the third to the oily residue content (table ). To ensure this quality, one or more filters and an air dryer are used at the outlet of the air compressors at the head of the pneumatic network.