Abstract: A device, e.g. a pressure regulator, for realizing an opening and/or closing function in connection with the force-velocity curves of the device incorporates two parts which work away from and towards each other at different velocities and accelerations, e.g. slide and housing. The parts work with a stroke and determine, in dependence upon the present size of the stroke, the passage of a fluid by way of a restrictor function realized by the parts. At least the one part (the slide) is subjected to force on both its sides. The restrictor function is made up of at least two part-restrictors which can be simultaneously actuated by a respective stroke and thereupon vary, preferably successively, their restrictor sizes differently from each other in dependence upon the respective stroke size. In the restrictor function, a passage of fluid is herein obtained which produces a smooth curve shape in the introductory and concluding part of the respective opening or closing function.