Abstract: A power wrench comprises a ring member for connection to the screw head to be rotated, the ring member being rotated with an engaging lever. The ratchet lever is driven by the piston rod of a piston. The piston has a convex circumferential surface so that it may be tilted within the cylinder in order to adapt to different orientations of the piston rod.

Abstract: The power wrench is provided with two pistons (38,41) arranged within each other. The pistons (38,41) abut against a pressure member (26) for pivoting a lever (18). The lever (18) is connected by an annular member (14) to the bolt head to be rotated. In a working stroke, the path of the first piston (38) is limited in that this piston impinges onto an abutment (46) while the second piston (41) moves on. The largest part of the working stroke is performed exclusively by the second piston (41) and thus is effected with low hydraulic throughput. When the force of the second piston (41) is not sufficient anymore, the working strokes are performed by both pistons (38,41) in common over the shorter piston path.

Abstract: The pressure-operated power wrench is provided with an annular member (14) rotatably supported within a headpiece (10). The annular member (14) can be coupled to the bolt to be rotated and is taken along in a moving direction by a ratchet lever (18). The lever (18) is actuated by a hydraulically moved piston (40). The piston (40) has a first piston face (45) and a second piston face (47) arranged coaxially thereto. When the load moment is small, only the first piston face (45) is pressurized. When this pressure exceeds a limit value, a back-check valve (57) is opened whereby also the second piston face (47) is pressurized. In the phase wherein rotation for tightening a bolt is still easy, only a small quantity of oil need be moved. Thus, power and heat losses are small. Further, the easy-rotating phase is abbreviated by fast reciprocation of the piston.

Abstract: The power wrench is provided with a hydraulic cylinder unit (12) and a wrench head (10). The cylinder unit (12) is movable with an arm (11) of the wrench head along a female guiding track (15), which is substantially parallel to the axis (16) of the wrench head (10). This way, the wrench head (10) may be less wide than the cylinder unit (12) and the cylinder unit (12) can be set so as not to collide with obstacles near the screw head to be turned.

Abstract: The power wrench comprises a housing (10) with a rearward housing member (12) which forms a protection against bursting for the hydraulic cylinder (27) arranged within the housing member (12). Through a joint (38, 40) and self-aligning, the piston (35) acts upon the lever (18) which is supported coaxially to the ring (14). The lever (18) comprises a ratchet element (17) being supported at the lever (18) by a semisperical pressure member (20). The power wrench can be submitted to extremely high hydraulic pressures without a danger to the environment.