Apparatus for feeding gas mixtures at the intake of a high pressure compressor the high pressure compressor configured to suck air or any other gas mixture at ambient pressure, the apparatus comprising: - a tubular mixing pipe which presents a first end suitable to be connected with the intake of a sucking manifold of a high pressure compressor; - a first gas intake device placed along said mixing pipe and suitable to inject inside said mixing pipe the gas which receives from a pressurized Helium source; - a second gas intake device placed along said mixing pipe, downstream said first gas intake device and suitable to inject inside said mixing pipe the gas which receives from a pressurized Oxygen source; - a first and a second Oxygen-measurement sensor placed along said mixing pipe, downstream respectively said first and said second gas intake device and suitable to measure/determine the percentage of Oxygen of the gas mixture which is in the region of said related Oxygen-measurement sensor (31, 32); - a first servo-controlled throttling valve interposed between said first gas intake device and said pressurized Helium source and suitable to adjust/control the gas flow directed towards said first gas intake device; - a second servo-controlled throttling valve interposed between said second gas intake device and said pressurized Oxygen source and suitable to adjust/control the gas flow directed towards said second gas intake device; - an electronic control unit configured in such a way as to drive said first and second throttling valve on the basis of the Oxygen percentages of said gas mixture measured/determined by said Oxygen-measurement sensors (31, 32), in such a way that the percentages of Oxygen, Nitrogen and Helium of said gas mixture coming out of said mixing pipe keep substantially equal to prefixed target percentages of Oxygen, Nitrogen and Helium, characterized in that it comprises a first auxiliary pressure regulator and a second auxiliary pressure regulator, both electrically connected with said electronic control unit suitable to manage the operation thereof, the first of which interposed between said first servo-controlled throttling valve and a high pressure manual regulator of said pressurized Helium source and suitable to vary the pressure of said Helium entering into said first servo-controlled throttling valve and the second of which interposed between said second servo-controlled throttling valve and a high pressure manual regulator of said pressurized Oxygen source and suitable to vary the pressure of said Oxygen entering into said second servo-controlled throttling valve. - a tubular mixing pipe which presents a first end suitable to be connected with the intake of a sucking manifold of a high pressure compressor; - a first gas intake device placed along said mixing pipe and suitable to inject inside said mixing pipe the gas which receives from a pressurized Helium source; - a second gas intake device placed along said mixing pipe, downstream said first gas intake device and suitable to inject inside said mixing pipe the gas which receives from a pressurized Oxygen source; - a first and a second Oxygen-measurement sensor placed along said mixing pipe, downstream respectively said first and said second gas intake device and suitable to measure/determine the percentage of Oxygen of the gas mixture which is in the region of said related Oxygen-measurement sensor (31, 32); - a first servo-controlled throttling valve interposed between said first gas intake device and said pressurized Helium source and suitable to adjust/control the gas flow directed towards said first gas intake device; - a second servo-controlled throttling valve interposed between said second gas intake device and said pressurized Oxygen source and suitable to adjust/control the gas flow directed towards said second gas intake device; - an electronic control unit configured in such a way as to drive said first and second throttling valve on the basis of the Oxygen percentages of said gas mixture measured/determined by said Oxygen-measurement sensors (31, 32), in such a way that the percentages of Oxygen, Nitrogen and Helium of said gas mixture coming out of said mixing pipe keep substantially equal to prefixed target percentages of Oxygen, Nitrogen and Helium,