A device for shutting off or regulating a medium flow, such as, for instance, a shutoff or an overflow slide, provided with a sliding plate (2) which is movably set up and which is connected with an adjusting mechanism (3, 4, 5) by means of which the sliding plate (2) can be set in different positions, characterized in that the device is further provided with a mounting plate (7) in which a passage opening (8) is provided, of which passage opening (8) the passage area can be shut off or regulated with the sliding plate (2), while the mounting plate (7) further serves for guiding the sliding plate (2), and to that end the sliding plate (2) is U-shaped at two opposed, first longitudinal edges (2a, 2a'), the two U-shaped parts embracing the corresponding longitudinal edges (7a, 7a') of the mounting plate (7).