| 摘要 |
PROBLEM TO BE SOLVED: To easily adjust rotational torque transmitted to a Kelly bar.SOLUTION: A torque limiter of this invention has a hydraulic motor 10 for disconnecting power transmission between a casing tube 4 and a Kelly bar 9 when transmitted torque exceeds upper limit torque set in advance, and sets the upper limit torque by connecting an outlet port of the hydraulic motor 10 with an inlet port through a relief valve 121. Further, a plurality of oil pressure setting valves 122, 123 and 124 capable of being connected with the relief valve 121 are provided, and by changing connection between the relief valve 121 and the oil pressure setting valves 122, 123 and 124, the upper limit torque can be changed. |
