Nitrogen/carbon dioxide mixing valves

Claim 1

Gas mixing and supply apparatus, comprising: (a) a first on/off valve adapted to be snapped between a fully open position and a fully closed position, said first valve being an inlet connectable to a source of a first gas under substantially constant pressure, and an outlet; (b) a second on/off valve adapted to be snapped between a fully open position and a fully closed position, said second valve having an inlet connectable to a source of a second gas under substantially constant pressure, and an outlet; (c) a mixing chamber having a first inlet connected to the outlet of said first valve, a second inlet connected to the outlet of said second valve, and an outlet on an outlet side thereof, said outlet being connectable to a pipeline for supplying a mixture of said first and second gases generated in said mixing chamber, to a point of use, (d) bias-providing bistable detent means adapted to restrict opening of the valves and to ensure that the valves snap from said fully open to said fully closed position and from said fully closed to said fully open position; and (e) actuating means for actuating said first and second valves, the actuating means being operable in dependence upon the gas pressure prevailing as an outlet pressure, in use, in said outlet side of the mixing chamber, such that, when the outlet pressure is at or below a predetermined lower value, the actuating means overcomes the bias of the detent means and causes the first and second valves to snap from said fully closed position to said fully open position, whereby the first and second gases mix within the mixing chamber until the outlet pressure attains a pre-determined upper value, whereupon the actuating means causes the first and second valves to snap from said fully open position to said fully closed position and that when the outlet pressure drops to said pre-determined lower value the actuating means causes the first and second valves to again snap into said fully open position until the said upper value of the outlet pressure is again attained, whereby the outlet pressure is, in use, maintained substantially within said upper and lower values.