Abstract: A medical gas production system produces from air a gas composition having a concentration of oxygen greater than the air for subsequent respiration by patients. The system includes a pair of treatment tanks, each containing an adsorbent bed for adsorbing gases from the air and a receiver tank for receiving an oxygen enriched gas mixture from the treatment tanks. A pair of transfer valves connected between receiver tank and respective ones of the treatment tanks control flow of gas from each treatment tank to the receiver tank, as well as enabling backflow of the gas mixture from the receiver tank to the treatment tank if a measured quality of the gas exiting the receiver tank falls below a prescribed threshold.