An air supply unit for a pneumatic system is provided herein. The unit includes a compressor inlet for receiving compressed air in a supply mode. The unit further includes a consumption outlet for connecting at least one consumption circuit. The unit further includes an air processing unit connected to the compressor inlet for drying and filtering the compressed air and delivering dried compressed air at its outlet. The unit further includes a supply line extending from the outlet to the consumption outlet. The unit further includes a purge tank connected to the supply line. The purge tank is connected to the supply line through a throttle for pressure reduction of the purge air. In order to realize a short filling time, the purge tank is further connected to the supply line by a filling valve. The filling valve is open in the supply mode and blocking in the purge mode.