NOVELTY - The gas mix installation comprises a main pump (8) that includes a suction side, an injection side and a unit for cutting, chopping or shredding any solids in a liquid and is externally arranged in a biogas reactors tank (1), where the pump is a shredder type pump, a liquid suction pipe (6) connecting an interior of the tank to the suction side, an injector pipe connecting the interior of the tank to the injection side, and a gas pipe (10) connected between the injector pipe and a source of biogas (9). The gas pipe is connected to the injector pipe externally of the tank.    USE - The gas mix installation is useful with a biogas reactor tank for producing biogas.    ADVANTAGE - The gas mix installation increases biogas yield and speeds up a biogas production process by providing improved mixing and processing of the organic materials in basic materials.    DETAILED DESCRIPTION - The gas mix installation comprises a main pump (8) that includes a suction side, an injection side and a unit for cutting, chopping or shredding any solids in a liquid and is externally arranged in a biogas reactors tank (1), where the pump is a shredder type pump, a liquid suction pipe (6) connecting an interior of the tank to the suction side, an injector pipe connecting the interior of the tank to the injection side, and a gas pipe (10) connected between the injector pipe and a source of biogas (9). The gas pipe is connected to the injector pipe externally of the tank. A gas pipe inlet in the injector pipe is arranged in a venturi device arranged in the injector pipe. The injector pipe upstream from a connection to the gas pipe is provided with a branch pipe, which is provided with a secondary injector pipe. A diameter of the injector pipe on a section of the injector pipe has an interior diameter of 60-100 mm. The injector pipe is arranged at an angle relative to a side of a wall of the tank, where the angle is 15-40 degrees C. A part of the injector pipe projects into the tank in use. The injector pipe is arranged at an angle relative to the wall of the tank in use, where the angle is different to the angle at which the suction pipe or the part of the suction pipe projects into the tank. The suction pipe in use is arranged below the injector pipe. The injector pipe has a longitudinal axis, and comprises a nozzle having an opening with a first diameter and connecting to a mixing chamber, where the mixing chamber in cross-section orthogonal to the longitudinal axis has a diameter larger than the first diameter, the mixing chamber connects to an ejector pipe, which in turn is connected to a transition pipe section that is conical and has a smallest diameter adjacent the ejector pipe. A diffuser is arranged in an opposite end of the transition pipe. An INDEPENDENT CLAIM is included for a method for increasing a gas yield from a biogas reactor tank.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a gas mix installation.    Biogas reactor tank (1)    Liquid suction pipe (6)    Main pump (8)    Source of biogas (9)    Gas pipe. (10)