Patent ID: 6837243

Claim:
A breathing gas system comprising: a primary breathing gas source; a primary gas delivery passageway for conveying breathing gas at a first operating pressure, the passageway in fluid communication with the primary breathing gas source and a breathing mask; a check valve disposed in the primary gas delivery passageway; a first valve responsive to primary breathing gas pressure, the first valve having a chamber in fluid communication with the primary gas delivery passageway, the first valve having a first valve passageway capable of alternating between an open and closed configuration, in the open configuration the first valve passageway is in fluid communication with an inlet to a first flow restrictor leading to a vent; a second valve responsive to primary breathing gas pressure, the second valve having a chamber disposed in fluid communication with the outlet of a second flow restrictor, the second flow restrictor having an inlet in fluid communication with the primary gas delivery passageway, the chamber also disposed in fluid communication with the passageway in the first valve, the second valve having a passageway capable of alternating between an open and closed configuration, in the open configuration the passageway is in fluid communication with a secondary breathing gas source and is in fluid communication with the breathing mask; the secondary breathing gas source capable of delivering secondary breathing gas at a second operating pressure; and, wherein the first and second valves are normally closed by the pressure of the primary breathing gas until a reduction of the primary breathing gas pressure causes the first valve to open, the opening of the first valve resulting in the primary breathing gas flowing to the vent, the venting of the primary breathing gas from the chamber of the second valve causing the second valve to open which allows secondary breathing gas to flow to the breathing mask.