Method and arrangement to accomplish a one-way flow

A method to accomplish a self-acting function with a flow in one direction in a conduit (2) with minimal flow resistance, characterized in that a one-way valve (1), which in an unaffected condition closes off the conduit (2), is of a flexible, elastic material and is arranged with a close fit in connection to the inner surface of the conduit (2), that the one-way valve (1) is partially fixed along the inner circumference of the conduit (2) by means of one or more parts of its outer surface having a longitudinal/circumferential extension in the conduit (2), in such a way that in case of pressure from a medium in one direction in the conduit (2) a possible flow is blocked due to the fact that pressure from the medium presses the non fixed parts of the one-way valve (1) against the inner surface of the conduit (2), forming a completely tight element and that under influence of pressure of the medium in the opposite direction, the non fixed parts of the one-way valve (1) are brought to collapse, whereby a flow dependent on the magnitude of the pressure is let through with negligible resistance.