Abstract: A method and an apparatus for separation and separate flow of gas and liquid in a flow system, e.g. a tube system, wherein there is flowing a liquid or a liquid mixture containing gas or giving off gas as a function of time and/or variable pressure. The gas (10, 11) is permitted to separate continuously from the liquid phase (9) and thereby establish and maintain a pneumatic system in pressure equilibrium with the hydraulic system, by separation of the two phases by means of at least one permeable blocking layer (7), e.g. of textile material, which is so arranged along the length of the flow system that the heaviest medium (9) at all times will be located on that side of the blocking layer configuration (7) conditioned by gravimetrical forces, at the same time as the layer, or a configuration of layers, allows a change of the available cross-section for the essentially two phases (8, 9) along the length of the flow system, in order to compensate for variations in quantity between the phases.