摘要 |
PROBLEM TO BE SOLVED: To provide a leader type pipe-driver capable of preventing an overload state applied to a mast in the case of the derricking works of a leader. SOLUTION: One end section of a leader derricking rope 10 is connected to the root attaching section 7A of a mast 7 through an overload preventive device 11 having an alarm means. The overload preventive device 11 has a cylinder 12 in which a base end section is connected to the root attaching section 7A of the mast 7, an expansion rod 14, which is urged in the shrinking direction by a spring 13 incorporated to the cylinder 12 and in which a projecting end section is connected at one end section of the leader derricking rope 10, a limit switch 16 on-off operated by a dog 15 fixed onto the expansion rod 14 and an overload alarm means operated by the limit switch 16.
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