A method of controlling the feed of a combustible gas by means of a valve device placed in a feed pipe which has a gas inlet section and a gas outlet section, the device comprising a valve seat in said pipe associated with a membrane-operated plug and means for returning the plug to a position in which the valve seat is shut off, said method comprising the following steps: - creating a pressure difference (Dp) in a section of the pipe downstream of said plug with respect to the direction of flow, by means of a constriction in the pipe having a predetermined cross section, said pressure difference (Dp) being defined by a first pressure (Pu) upstream of the constriction and a second pressure (Pe) downstream of said constriction, - collecting the signal formed by said second pressure (Pe) downstream of said constriction and making said second pressure act on the side of the membrane opposite that on which the first pressure (Pu) acts, - generating a regulatable load (F; F') on the membrane of said membrane operating system, this load being independent of said first and second pressures (Pu, Pe), such that the pressure difference (Dp) can be regulated by regulating said load (F, F') acting on the membrane, said load being correlated proportionally with said difference, in such a way that the flow rate of the gas fed to the outlet section, which is a function of said pressure difference (Dp), is controlled independently of the pressure levels present in the inlet section and in the outlet section of said pipe, characterized in that said valve device is made in the form of a servo valve, and in that said method includes the following steps: - collecting the signals formed by said first and second pressures (Pu, Pe) across the constriction, by means of corresponding pipes, and bringing said pressures to opposite sides of a second membrane of a pressure regulator fitted in a control circuit of the servo valve, - generating said regulatable load (F') on said second membrane of the pressure regulator only, independently of said first and second pressures, in such a way that the pressure difference (Dp) can be regulated by regulating the load acting on said second membrane, the load being correlated proportionally with said pressure difference, in such a way that the flow rate of the gas fed to the outlet section, which is a function of said pressure difference, is controlled independently of the absolute pressure levels present in the inlet section and in the outlet section of said pipe. - creating a pressure difference (Dp) in a section of the pipe downstream of said plug with respect to the direction of flow, by means of a constriction in the pipe having a predetermined cross section, said pressure difference (Dp) being defined by a first pressure (Pu) upstream of the constriction and a second pressure (Pe) downstream of said constriction, - collecting the signal formed by said second pressure (Pe) downstream of said constriction and making said second pressure act on the side of the membrane opposite that on which the first pressure (Pu) acts, - generating a regulatable load (F; F') on the membrane of said membrane operating system, this load being independent of said first and second pressures (Pu, Pe), such that the pressure difference (Dp) can be regulated by regulating said load (F, F') acting on the membrane, said load being correlated proportionally with said difference, in such a way that the flow rate of the gas fed to the outlet section, which is a function of said pressure difference (Dp), is controlled independently of the pressure levels present in the inlet section and in the outlet section of said pipe, - collecting the signals formed by said first and second pressures (Pu, Pe) across the constriction, by means of corresponding pipes, and bringing said pressures to opposite sides of a second membrane of a pressure regulator fitted in a control circuit of the servo valve, - generating said regulatable load (F') on said second membrane of the pressure regulator only, independently of said first and second pressures, in such a way that the pressure difference (Dp) can be regulated by regulating the load acting on said second membrane, the load being correlated proportionally with said pressure difference, in such a way that the flow rate of the gas fed to the outlet section, which is a function of said pressure difference, is controlled independently of the absolute pressure levels present in the inlet section and in the outlet section of said pipe.