Abstract: A valve housing has a mouth port in one side and a vent opening in its opposite side, with another opening between them for connection to a carbon dioxide removing and oxygen generating canister. Around the mouth port inside the housing is a valve seat, toward which a valve member is urged by a spring to normally close the valve. Surrounding the valve member and spring is a bellows that has an open end secured to the housing around the vent opening to thereby expose the inside of the bellows to the pressure of water or other liquid in which the valve may be submerged. Connected to the outer end of the mouthport is a mouthpiece adapted to be held in the mouth of a user, and encircling the mouthpiece is a ring that is connected with the valve member for movement with it.