Abstract: A valve for a carbonator having an internal check valve movable between two operable positions depending upon whether the carbon dioxide or the pressure water has the greater pressure, (these being the ingredients of the carbonated fluid being sought). When the carbon dioxide positions the check valve, venting openings having an aligned relation cause harmless venting of the carbon dioxide to atmosphere, thereby obviating any possible contamination of the water source by the carbon dioxide. When the pressure water positions the check valve, a consequence of such movement is that a sealing ring occupies an interposed position between the venting openings to prevent any water leakage therethrough during this interval of operation.