Power unit for positioning valves, or the like, into desired position

A pressure-fluid-operated power unit producing a rotating motion for positioning valves, or similar actuators, into a desired position, the rotating motion of the actuator being a multiple of about 90°, the power unit comprising:

• a cylindrical casing, a first end flange and a second end flange being provided at the ends of the casing;
• an annular cylinder space;
• at least two pairs of pistons, the pistons being movable with respect to each other and substantially of the same shape and size as the cross-section of the cylinder space, the first pistons in each piston pair being movably arranged with respect to the cylinder space, the first pistons rotating about its axis to allow the first pistons to move in the cylinder space in the direction of its circumference, and the second pistons of the piston pair adjacent to the second end flange being immovably arranged with respect to the second end flange or the casing of the cylinder space;
• a transmission shaft arranged to rotate about the axis of the cylinder space with said first pistons for transmitting power for the positioning of the actuator;
• at least one additional annular cylinder space being arranged coaxially with the cylinder space between the first end flange and the second end flange;
• the cylinder space adjacent to the additional cylinder space and additional cylinder spaces being separated from each other by an intermediate flange which is arranged to move with respect to the cylinder space and the additional cylinder spaces and the transmission shaft, the flange rotating about their axis;
• the additional cylinder space being provided with at least two pairs of additional pistons, the additional pistons of which are substantially of the same shape and size as the cross-section of the additional cylinder space;
• second additional pistons of the additional piston pairs being arranged to the additional cylinder space limited by the second end flange are immovably fastened with regard to the second end flange or the casing of the cylinder space, and second additional pistons being arranged to other additional cylinder spaces as well as second pistons of the cylinder space being fastened to the intermediate flange, on the opposite side of which are fastened the first additional pistons of the adjacent additional cylinder space;
• additional piston pairs being arranged into one and the same additional cylinder space being movable with respect to each other in the direction of the circumference of the additional cylinder space;
• pressure fluid conduits for leading pressure fluid into and out of the spaces between the pistons and the additional pistons.