Abstract: A sealing ring device is provided for a fluid valve having a piston (2) reciprocating within a cylinder (1), wherein the piston (2) includes a valve cone (2c) adapted to contact a valve seat (11). In order to seal the inner space of the cylinder (1) located behind the piston (2) from an inlet/outlet passageway (A), a resilient sealing ring (5) is disposed in an annular groove (4) opening into the cylinder (1) around the rear end (2a) of the piston (2). A press ring (7), which extends above the rear end (2a) of the piston (2), contains the sealing ring (5) in the annular groove (4). A spring element (8) rests on the press ring (7). A piston rod (3) is guided in slidable manner through the piston (2). A stop (9) is attached to the rod (3) above the rear end (2a) and opposite the top side of the spring element (8).

Abstract: A pneumatic positioner with a casing composed of a shell-like bottom part and a shell-like cover part. A membrane plate, is connected through a gas-tight membrane with the side walls of the casing so as to be movable back and forth in the casing in the direction of a drive spindle which is disposed in sealing relationship through the bottom part of the casing. In the bottom part and/or in the cover part, there are arranged one or more gas-conducting connecting pieces. In the casing there are arranged coil springs for producing biasing or restoring forces. These springs abut, on the one hand, the membrane plate and, on the other hand, the bottom part or cover part. On the membrane plate of one embodiment there is provided for each coil spring at least two supporting surfaces which present different spacings from a plane perpendicular to the direction of motion of the drive spindle and upon which the coil springs are replaceably disposed.