The pre-filter removes solid particles (> 0.01 µm) and oil residue from the air that is to be dried. The air then flows through the inlet valve and lower diffuser into one of the two desiccant tanks. The desiccant traps the moisture, leaving the dried compressed air to exit the desiccant tank via the upper diffuser. The main flow of dried compressed air then finally reaches the compressed air network via a check valve and the downstream dust filter. A small portion of the dried compressed air is drawn off as purge air via a control valve and alternately regenerates the desiccant in whichever tank is not in use.