A system for non-invasive ventilation comprising: a gas source conduit adapted to be fluidly coupled at a first end to a gas source and comprising at a second end a bifurcation having a first branch and a second branch; a primary flow path conduit adapted to be coupled to the first branch of the bifurcation as part of a primary flow path ; a flushing flow path conduit adapted to be coupled to the second branch of the bifurcation as part of a flushing flow path having a higher resistance to gas flow than primary flow path ; a patient interface comprising a breathing chamber and a nasal flow delivery part, constructed such that the breathing chamber is in the primary flow path and the nasal flow delivery part is in the flushing flow path ; a control assembly coupled or adapted to be coupled to the primary flow path , the control assembly comprising a movable member movable between a first position in which the movable member increases the resistance to gas flow through the primary flow path and a second position in which the movable member does not increase the resistance to gas flow through the primary flow path , the movable member configured to move between the first position and the second position in response to pressure changes within the breathing chamber of the patient interface ; and wherein the movable member is configured to move to the first position when gas pressure within the breathing chamber of the patient interface is greater than about a gas source pressure and move to the second position when gas pressure within the breathing chamber is less than or equal to about a gas source pressure. a gas source conduit adapted to be fluidly coupled at a first end to a gas source and comprising at a second end a bifurcation having a first branch and a second branch; a primary flow path conduit adapted to be coupled to the first branch of the bifurcation as part of a primary flow path ; a flushing flow path conduit adapted to be coupled to the second branch of the bifurcation as part of a flushing flow path having a higher resistance to gas flow than primary flow path ; a patient interface comprising a breathing chamber and a nasal flow delivery part, constructed such that the breathing chamber is in the primary flow path and the nasal flow delivery part is in the flushing flow path ; a control assembly coupled or adapted to be coupled to the primary flow path , the control assembly comprising a movable member movable between a first position in which the movable member increases the resistance to gas flow through the primary flow path and a second position in which the movable member does not increase the resistance to gas flow through the primary flow path , the movable member configured to move between the first position and the second position in response to pressure changes within the breathing chamber of the patient interface ; and wherein the movable member is configured to move to the first position when gas pressure within the breathing chamber of the patient interface is greater than about a gas source pressure and move to the second position when gas pressure within the breathing chamber is less than or equal to about a gas source pressure. <EOS>