Reducing valve assembly with spherically shaped operating part

In a reducing valve assembly, including a fluid inlet port (112) and a fluid outlet port (116), with a main valve for controlling flow therethrough, wherein said main valve includes a valve member (118) movable with respect to a main valve seat (114) and actuated by an operating part comprising a piston (120) having a piston rod (1) extending toward the main valve seat and engageable with the main valve member for moving the main valve member away from the main valve seat, the improvement comprising the piston (120a) being connected in cantilever fashion to only an end of the piston rod, said piston being slidably mounted in a cylinder of the valve assembly to act as the sole guiding mechanism for movement of the piston rod, a movable wall having an approximately circular section through the center of said piston and being spaced from said valve seat, said movable wall extending outwardly in a diametrical direction from said piston rod to said piston, said piston having an outer peripheral wall connected directly to said movable wall, said outer peripheral wall carrying the outer maximum diameter of said piston, said movable wall having a flat annular section (2a) directed around said approximately circular section under said piston, with the ratio between the maximum diameter of said approximately circular section to the maximum diameter of the piston being in the range of from about 0.4 to 0.7.