the development of earth's snake from a grabenlos laid pipe

摘要

A scraper for removing an earth core from a pipe laid without excavation by ramming or pressing has a sledge (4), a hydraulic jack (6) and clamping devices (8, 11). The sledge (4) is linked to the piston rod (10) of the hydraulic jack (6) and to a first clamping device (11) and the housing (7) of the hydraulic jack (6) is linked to a second clamping device (8). The clamping devices (8, 11) may be alternatively moved into a clamping position in which they may be pressed against the inner wall of a pipe (2) and into a released position in which they are released from the inner wall of the pipe (2). The clamping devices may be actuated by hydraulic clamping cylinders (34, 74). The hydraulic jack (6) has a sensor that generates a control signal when an end position of the hydraulic jack (6) is reached. A control valve is provided to control the hydraulic jack (6) and the clamping cylinder (34, 74). The control valve automatically controls the working direction of the hydraulic drives depending on the control signal generated by the sensor.