| 摘要 |
For installing a cable-duct (1) around a cable (3) buried in the ground the duct is propelled by propelling means (17) which comprise solenoid means (49) and a corresponding core member (53) of a magnetic material, and duct transporting means (47). The core member is provided with coupling means (55) for coupling to the free end of the cable, and the solenoid means are driven by a current as to maintain during operation the free end of the longitudinal member coupled to the core member in a fixed position with respect to the transporting means. The propelling operation is supported by feeding a fluid under pressure through the duct, the foremost end of the duct being provided with a spouting member. Suitable design of the core member in combination with a suitably varying current for driving the solenoid allow more dynamical propelling operation, and consequently better performance.
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