An exhaust assembly (1) adapted for use in a respiratory gas delivery system comprises an exhaust vent, an exhaust gas flow passage, a primary gas flow passage, and a moveable member. The exhaust gas flow passage communicated a flow of exhaust gas from a first end of the exhaust assembly to the exhaust vent. The exhaust vent communicates the exhaust gas from the exhaust gas flow passage to ambient atmosphere. The primary gas flow passage communicates a flow of supply gas from a second end of the exhaust assembly to the first end of the exhaust assembly. The moveable member defines at least a portion of the exhaust gas flow passage and the primary gas flow passage, is operable to isolate the flow of exhaust gas from the flow of supply gas, and is responsive to a pressure differential between the flow of supply gas and the flow of exhaust gas.
