| 摘要 |
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.
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