A pressure control valve for regulating the gas pressure in a conduit is composed of two chambers, one of which receives control fluid under well-defined pressure for the purpose of adjusting the pressure of the medium in the second chamber and in the conduit to follow changes of the control fluid pressure. A soft, non-resilient double diaphragm divides the two chambers and the space between the two diaphragms is accessible from the outside and may be supplied with gas or fluid at higher pressure. The valve has a compensating piston which is attached to the diaphragms and glides in a blind bore the end of which communicates with the second chamber in which the pressure is controlled.