Abstract: A fluid pressure actuator (1) having two pistons (5,6) and a associated toothed rack portions (7,8) for activating an actuating member (10) via a toothed wheel (9) enables the piston positions to be adjusted, both in the full-strokes position of the actuating member (10) and in its zero-position. To this end, one end-wall (4) of the actuator has provided therein an adjusting screw (16) which engages the one piston (16). The piston, in turn, is provided with an adjusting screw (17) which engages the rack portion (7) of the opposing piston (5). This latter adjusting screw (17) can be reached through a plugged entry port (4d) in the end-wall (4).

Abstract: In a pressurized operated actuator (1) for stepwise regulation of valves between at least three distinct positions, one end-wall has been removed and replaced with an auxiliary actuator (19) having a piston (21) whose piston area exceeds the sum of the areas of the conventional pistons (5 and 6) of the firstmentioned actuator. The piston (21) of the auxiliary actuator has a piston rod (22) which extends into the cylinder chamber (2a) of the actuator. Its stroke equals half the length of the stroke of the rods (7 and 8) of two conventional pistons (5 and 6). The firstmentioned piston rod (22) limits the movement of the pistons (5 and 6) of the actuator in a direction away from one another. In this way, there can be obtained a distinct intermediate position for the rotary settings of the actuator.

Abstract: A pneumatic operating device, e.g. for controlling valves, includes a cylinder (2) in which a piston (12) is movable. The piston has an axially extending rack part (11) having teeth which engage with teeth on an operating element (10) arranged in the cylinder wall (2b) for rotation transversely of the longitudinal axis of the piston and passing sealingly through said cylinder wall. The piston (12) is provided on the side opposite its rack part with a recess (24) for receiving a part of a spring (26) for the return movement of the piston. The recess (24) extends substantially into the rack part (11) of the piston, preferably through a distance of such length that it extends axially approximately up to or beyond a radial line perpendicular to the piston axis through the center of rotation of the operating element even when the piston is in a position in which the spring is compressed to its maximum.