Separator of a mixture of liquid and gas, comprising an injection device, a separation chamber having a substantially cylindrical internal surface and extending along a vertical longitudinal axis, and a control chamber, in which: - the injection device is fed by the mixture of liquid and gas, and injects the mixture into the separation chamber, in a manner that is substantially tangential to the internal surface, such that the mixture is separated in the separation chamber into gas situated in a central volume and liquid situated in an annular volume around the central volume, an interface surface separating the said central and annular volumes, - the separation chamber extends downwards between an upstream wall close to the injection device and a downstream wall opposite to the upstream wall, and comprises a first axial outlet for extracting the gas from the central volume, a second outlet at a distance from the said axis for extracting the liquid from the annular volume, and a third axial outlet in communication with the control chamber, the said third outlet located in the downstream wall and having a diameter (D 5)greater than the diameter of the first outlet (D 4) and smaller than an internal diameter (D 3) of the second outlet, - the control chamber is in the extension of the separation chamber and receives through the third outlet of the separation chamber a quantity of liquid which flows from the separation chamber to form a volume of liquid having an upper surface, and is connected to the injection device by a return circuit to reinject a quantity of liquid from the said control chamber to the injection device, and - a regulation means comprising a pump and suitable for regulating a level of the upper surface in the control chamber by reinjecting the quantity of liquid through the return circuit to the injection device, and such that the said interface surface has, in normal operating conditions, a diameter (D c) lying between the diameter of the first outlet (D 4) and the diameter of the third outlet (D 5) so that the said interface surface enters the control chamber and the liquid from the separation chamber flows to the said control chamber. - the injection device is fed by the mixture of liquid and gas, and injects the mixture into the separation chamber, in a manner that is substantially tangential to the internal surface, such that the mixture is separated in the separation chamber into gas situated in a central volume and liquid situated in an annular volume around the central volume, an interface surface separating the said central and annular volumes, - the separation chamber extends downwards between an upstream wall close to the injection device and a downstream wall opposite to the upstream wall, and comprises a first axial outlet for extracting the gas from the central volume, a second outlet at a distance from the said axis for extracting the liquid from the annular volume, and a third axial outlet in communication with the control chamber, the said third outlet located in the downstream wall and having a diameter (D 5)greater than the diameter of the first outlet (D 4) and smaller than an internal diameter (D 3) of the second outlet, - the control chamber is in the extension of the separation chamber and receives through the third outlet of the separation chamber a quantity of liquid which flows from the separation chamber to form a volume of liquid having an upper surface, and is connected to the injection device by a return circuit to reinject a quantity of liquid from the said control chamber to the injection device, and - a regulation means comprising a pump and suitable for regulating a level of the upper surface in the control chamber by reinjecting the quantity of liquid through the return circuit to the injection device, and such that the said interface surface has, in normal operating conditions, a diameter (D c) lying between the diameter of the first outlet (D 4) and the diameter of the third outlet (D 5) so that the said interface surface enters the control chamber and the liquid from the separation chamber flows to the said control chamber.