PRESSURE CONTROLLER

In a proportioning valve integrated into or connected to the housing (3) of a master cylinder of a vehicle brake system, the valve closure member (30) is provided on a control piston (23) which is slidable by the action of fluid pressure against the force of a control spring (45). With its end remote from the valve closure member (30), the control piston (23) projects into a chamber (46) which is sealed against the master cylinder pressure. The chamber (46) communicates, via the channel (47), with the master cylinder reservoir. As the chamber (46) is therefore not in direct communication with the atmosphere, the displacing motion of the control piston (23) will not be impaired by contamination or corrosion; it also cannot be impaired by the development of an increased pressure or a pressure below atmospheric pressure in the chamber (46). An arrangement of two in-line valves integrated into a tandem master cylinder housing is also described (Fig. 5 not shown).