Pressure demand regulator with automatic shut-off

In a pressure-demand breathing apparatus including a face mask providing a mask chamber when fitted against the face of a user, and means including an air supply line for connecting said mask to a pressurized air supply, a pressure demand regulator positioned in said air supply line between said face mask and said air supply,

• said pressure-demand regulator including means responsive to pressure within said mask chamber for admitting said pressurized air to said mask chamber at flow rates required for normal breathing or abnormally deep breathing when said mask is worn and for maintaining a predetermined positive pressure in the mask chamber above ambient pressure when said mask is fitted against the face of a user, said regulator also admitting said pressurized air to said mask at a predetermined high air flow rate substantially greater than that required either for normal breathing or for abnormally deep breathing when said mask is removed the improvement comprising shut off means for interrupting air flow from said air supply to said mask chamber and time delay means for preventing said shut-off means from interrupting said air flow for a predetermined period of time, wherein said shut-off means is responsive to said air flow and time delay means to interrupt the supply of air to said mask automatically upon sustained high flow through said regulator at a rate exceeding that required even for abnormally deep breathing which occurs for a time exceeding said predetermined period of time, whereby, said shut off means differentiates between temporary, user-induced high flow rates only momentarily exceeding that required even for abnormally deep breathing and sustained high flow rates exceeding said preselected values, such as occur when said mask is removed from the face of a user and open to ambient atmosphere, said shut-off means operating to interrupt the air supply only in the event of such sustained high flow rates.