A pressure regulator which maintains a constant ratio of pressures at two gas outlets is described. The device consists of three chambers, a central reference chamber; and two side chambers, each one separated from the central one by a double diaphragm. The two double diaphragms are connected to two valves that control the respective gas flows into the side chambers. In this way, the pressures in the side chambers are governed by the pressure in the central reference chamber. The individual diaphragms of one double diaphragm are of identical diameter; whereas, the other double diaphragm consists of two single diaphragms of different diameters. The areas of these diaphragms determine the constant ratio of the outlet pressures from the side chambers.