| 摘要 |
PROBLEM TO BE SOLVED: To execute long-distance work reducing driving force by injecting a lubricant from a plurality of places of a small bore propulsion pipe. SOLUTION: A plurality of relief valves 7 with the valve bodies formed of a synthetic resin are fitted to a propulsion pipe 1, and the working pressure of each relief valve 7 is according to the distance from a filling device 9. Each relief valve 7 is connected to the filling device 9 by an injection pipe 10 to propel the propulsion pipe 1. During propulsion of the propulsion pipe 1, a lubricant is injected between the propulsion pipe 1 and the natural ground through each relief valve 7 if necessary. Upon completing propulsion of propulsion pipe 1, the valve body, formed of the synthetic resin, of each relief valve 7 protruded from the inner surface of the propulsion pipe 1 is cut by a cutter provided at a self-advancing vehicle, and recovered together with the injection pipe 10.
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