| 摘要 |
PROBLEM TO BE SOLVED: To inexpensively manufacture a fastening device such as a bolt having simple structure and high fastening reliability. SOLUTION: Actuating a device through selecting a relief valve PV1 by a solenoid operated directional control valve V actuates respective hydraulic motors M1-M6 in order by a fastening torque of a 1/4 of final value set to a pressure switch PS1, to fasten a bolt, etc. Then a relief valve PV2 is selected to actuate the device, and at that time the respective hydraulic motors are actuated in order by a fastening torque of a 1/2 of final value set to a pressure switch PS2 to fasten the bolt, etc. Finally a relief valve PV3 is selected to actuate the device, and at that time the respective hydraulic motors are actuated in order by the fastening torque of the final value set to a pressure switch PS3 to fasten the bolt, etc. The device can be simplified because of the common use of the pressure switches PS1-PS3 to the respective hydraulic motors.
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