A control circuit for automatically stopping the flow of a gas in a primary circuit, includes a valve, a sensor and a controller. The valve is couplable with a primary pressure-regulator that controls the flow of another gas in a primary circuit. The valve has an inlet operable to receive a gas and an outlet operable to distribute the gas. The sensor is positionable in the primary circuit and operable to sense a parameter of the flow of the gas in the primary circuit and generate a signal that represents the sensed parameter. The controller is operable to receive the sensor's signal and, in response to the signal, direct the valve to close if the parameter of the flow of gas in the primary circuit lies outside of a predetermined range.