| 摘要 |
A suction head or a pick-up roll in a paper machine is mounted on a pivotable lever and is movable therewith between an operative position, an intermediate position at a short distance from the operative position, and a retracted position at a substantial distance from the operative position by two hydraulic cylinder and piston units whose cylinders are articulately connected to the frame and whose piston rods are articulately connected to the lever. The piston rods are rigid with first pistons, and each unit further comprises an annular second piston which surrounds the respective piston rod. Admission of pressurized fluid into a first chamber of each cylinder results in movement of the second pistons from first to second positions to thereby move the lever from operative to intermediate position through the medium of the first pistons and piston rods. The lever is pivoted to retracted position by admitting fluid into a second chamber of each cylinder to thus move the first pistons relative to the second pistons. The lever can be returned to operative position by admitting fluid into a third chamber of each cylinder and by relieving the pressure of fluid in the first chamber so that the first pistons first move relative to and thereupon together with the second pistons.
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