| 摘要 |
A rotary hammer which comprises a tool holder (2), an air cushion hammering mechanism which comprises a piston (9) and a beat piece (21) slideably located in a cylinder (8') so that reciprocation of the piston in the cylinder will cause the beat piece to hit a tool located in the tool holder; and means for causing the cylinder to rotate in addition to, or instead of, reciprocation of the piston in order to cause a tool located in the tool holder to rotate. The piston (9) is formed from a plastics material and is sealed in the cylinder (8') by means of an annular seal (27) that is located within an annular groove (26) in the piston. The annular seal has an inner diameter that is greater than the diameter of the radially outwardly directed surface of the groove, and the groove has an axial dimension that is greater than that of the annular seal, so that when the cylinder rotates about the piston (without reciprocation of the piston) the seal (26) will rotate with the cylinder (8').
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