Vent valve assembly

1. A vent valve apparatus for use with a system for supplying, from a gas supply, breathable gas pressurized above atmospheric pressure to a human or an animal, the apparatus including:

a gas washout vent;

a vent valve associated with the gas washout vent and being adapted to progressively restrict the flow area of the washout vent; and

a pressure sensitive control associated with the vent valve and being adapted to progressively cause said vent valve to restrict the flow area of the washout vent in response to increases in the pressure of the gas supply, thereby substantially regulating the flow of gas through the washout vent over a range of gas supply pressures.

2. An apparatus as claimed in claim 1 , wherein the vent valve is a plug connected to the pressure sensitive control such that movement of the pressure sensitive control causes a responsive movement of the plug.

3. An apparatus as claimed in claim 1 , in combination with a CPAP apparatus.

4. An apparatus as claimed in claim 1 , further comprising a conduit in communication with the gas washout vent to provide a supply of pressurized gas.

5. An apparatus as claimed in claim 4 , wherein the gas washout vent is fixed with respect to the conduit.

6. An apparatus as claimed in claim 4 , wherein the gas washout vent is an orifice in the conduit.

7. An apparatus as claimed in claim 4 , further comprising a branch extending from the conduit, and wherein the gas washout vent is an orifice in the branch.

8. An apparatus as claimed in claim 4 , wherein the vent valve is a plug movable with respect to the conduit.