Abstract: Using conventional manufacturing methods, porous, sintered, compacted powder bodies shaped as straight cylinders can be produced with extremely small variations in their flow resistance to a fluid. According to the invention, such bodies are produced in series so that, for a certain fluid and a certain pressure drop above the body, they produce a predetermined flow which can easily be regulated by using simple pressure-regulating equipment for controlling the pressure drop. The invention comprises an apparatus consisting of a pipe with pressure-regulating means, a container for a body according to the invention, and a series of bodies with different flow resistance for setting different flow intervals in the pipe for given fluids. The invention also comprises a method for setting a predetermined flow for a specific fluid at a given pressure, and the use of well defined porous bodies enabling a desired pressure to be set by regulating the pressure drop across the body.