The purification system of a compressed air system consists out of staged filtration and drying systems. As the compressed air has to travel through filter elements, heat exchanges or desiccant layers with small diameters and many bends pressure is lost. Corrosion, retained particles or absorbed oil & water clog filters and dryers and cause significant pressure drops which is a loss of energy. Monitoring the pressure drop is easily performed by utilizing a pressure sensor up-streams and another one down-streams and calculating the differential pressure. The gained information helps for efficiently timing filter element exchange and dryer overhauls.