A flow diverter valve (12) is used in controlling the pressure and/or flow rate of a breathable gas supplied to the airways of a patient by a breathable gas flow generator supply apparatus (11) during, for example, ventilatory assistance treatments such as non-invasive positive pressure ventilation and nasal Continuous Positive Airway Pressure (CPAP) treatment of Obstructive Sleep Apnea. The flow diverter valve includes a vane (10) and a housing (14). The housing has an inlet port (16), an outlet port (18), and an exhaust port (20). The exhaust port opens to atmosphere, and the inlet port is in fluid communication with the flow generator (22). The outlet port is in fluid communication with a patient mask (54) via a conduit (52). The vane is configured with respect to the housing such that a blower associated with the CPAP apparatus remains substantially unchoked, regardless of whether the vane is in the open or closed position. <；IMAGE>；
