A compressed air supply system for supplying compressed air to a pneumatic system is disclosed. The compressed air supply system comprises a compressed air input port, a compressed air output port and a vent port, a pneumatic main pipe arranged between the compressed air input port and the compressed air output port, a pneumatic vent pipe arranged between the compressed air output port and the vent port and connected to the pneumatic main pipe, a purge valve arranged in the pneumatic vent pipe for venting the compressed air supply system, a regeneration valve for controlling a regeneration flow of compressed air through an air dryer arranged in the main pipe, a governor valve for generating a pressure signal, and a first and a second pneumatic control pipe.