A continuous positive airway pressure (CPAP) system provides positive airway pressure therapy. It has been recognized that users generally prefer to breathe freely rather than to fight the pressurized air when possible. A continuous positive airway pressure (CPAP) system provides positive airway pressure therapy when required, but allows the user to breathe freely with the mask on when positive airway pressure is not required. The system has a valve that moves between two positions to open and close the unassisted breathing vent and the outlet from the flow generator.
