LEADING TUBE PROPULSION METHOD AND LEADING TUBE PROPELLING DEVICE

摘要

PURPOSE: To effectuate a re-advance by temporarily increasing the preset maximum propulsion force, when a propulsion load becomes equal to the force over the preset time during the propulsion of a rod tube. ;CONSTITUTION: A controller 5 receives from a position detecting sensor 14, a signal showing that a leading tube 10 or rod tubes sequentially jointed thereto, even if propelled, are still in such state as not exceeding the length of a rod tube to be jointed next. In this case, a propulsion load becomes equal to relief pressure as the first maximum propulsion force, and a hydraulic circuit is relieved. When this stop condition continues over the preset time, a booster signal is transmitted to a variable relief valve 31 for the preset time. As a result, pressure is raised to such relief pressure as the second maximum propulsion force, thereby effectuating a re-advance, regardless of the temporary interruption of an advance motion. Also, a pressure rise time is short and hydraulic equipment are, therefore, almost free from an adverse effect. Furthermore, a burden on an operator is lessened, due to automatic control via the controller 5.;COPYRIGHT: (C)1995,JPO