A single stage vacuum breaker flow regulator includes a diaphragm retained in an elevated position in between atmosphere and an outlet chamber for a gaseous medium. A valve in communication with an inlet chamber is yieldingly urged to a closed position by a spring. Cam levers are movable by the diaphragm upon a reduction in pressure to sub-atmospheric in the outlet chamber. The movement of said cam levers in response to a reduction in pressure is transmitted to a yieldingly movable valve to open said valve to the flow of gas from said inlet chamber to said outlet chamber.