A separator of a mixture of liquid and gas, comprising an injection device, a separation chamber having a cylindrical internal surface and extending along a vertical axis, and a control chamber. The mixture is separated in the separation chamber into gas and liquid, with a cylindrical interface surface. The separation chamber comprises a first axial outlet for extracting the gas, a second outlet for extracting the liquid, and a third axial outlet in communication with the control chamber. The interface surface has, in normal operating conditions, a diameter lying between the diameter of the first outlet and the diameter of the third outlet. The control chamber is connected to the injection device by a return circuit.