Abstract: An arrangement in a circulation lubrication system, the arrangement including a control mechanism for controlling the flow of lubricating oil supplied to a part to be lubricated. The control mechanism includes two interfitting tubes with apertures in walls of both of the tubes. The apertures are arranged to provide a flow orifice for the lubricating oil, and the tubes are arranged to be rotatable around their common symmetry axis to the effect that an angular position of the tubes in relation to one another changes and the apertures in the tube walls shift in a circumferential direction of the tubes by their relation to one another, thereby a change in a size of the flow orifice is provided by the apertures. The rotating movements of the tubes are produced by different transmissions.