Abstract: A self-regulating valve device adapted for use with respiratory equipment of a type which produces a pressurized flow of breathing gas. The valve device affords automatic access to the ambient atmosphere in the event of respiratory equipment malfunction and includes a primary inlet, a secondary inlet and an outlet. The primary inlet is adapted for connection to a ported exhalation valve which, in turn, is connected to one end of an elongated flexible tube, the opposite end of which is connected to a gas flow generator. The outlet, in turn, is connected to the inlet of an oral, nasal or oral/nasal respiratory mask respectively adapted to cover the patient's mouth, nose or mouth and nose. The valve device further comprises a pressure-responsive valve element for regulating gas flow into the inlet of the respiratory mask. In accordance with a further aspect of the invention, there is additionally provided a diffuser element positioned generally at the valve outlet/mask inlet junction.