Abstract: The invention relates to a hydraulic blocking valve, a so-called holding valve (10), the shutting-off member of which consists of a movable ball (16) coacting with a seat (17) in an inlet chamber (24). The space (15) on the side of the ball opposite its seat forms an operating chamber (15), and both chambers are joined by a constriction passage (13) counteracting flow of hydraulic liquid between the chambers. The operating chamber (15) is in communication with valve means (32) by the aid of which the pressure in the operating chamber can be heavily reduced, e.g. by being taken to a tank (44), resulting in that the ball (16) is thrust from its seat (17) to open the valve. A throttling means (25, 26) simultaneously comes into action for reducing the flow, i.e. liquid loss through the valve means (32) from the operating chamber (15). When the valve means is subsequently closed, pressure is once again built up against the ball so that the latter is pushed towards its seat (17) for closing the valve (10).