Abstract: An earth discharge control system for a small-diameter pipe propelling machine controls the excavated earth discharging operation of the small-diameter pipe propelling machine. The small-pipe propelling machine propels a small-diameter pipe (2) joined at its leading end to a leading pipe (1) into the ground by a propelling unit (3) installed in a starting shaft (4). Earth excavated by a cutting head (8) supported on the leading end of the leading pipe (1) is conveyed toward the starting shaft (4) by a screw conveyor (6) disposed within the small-diameter pipe (1). A pneumatically operated control valve (10) is disposed in combination with a portion of the screw conveyor (6) within the leading pipe (1).

Abstract: A pulse signal transfer control circuit is located between an input pulse detecting circuit for detecting the arrival of an externally applied input pulse and outputting a pulse signal with a predetermined pulse width, and an R-S flip-flop. The transfer control circuit prohibits the pulse signal from being transferred to the R-S flip-flop during a period in which the R-S flip-flop is set, a period of generation of a first internal clock signal, and a period of generation of a second internal clock signal, and allows the pulse signal to be transferred to the first R-S flip-flop during period in which the first and second clock signals are not generated and the period in which the first R-S flip-flop is reset.

Abstract: A pebble-stone crushing device for use in an excavator for laying pipelines underground has a plurality of rotor teeth formed integrally with the rear face of a cutter head which is mounted in the most front part of an excavator body to excavate a working face in front thereof, and a plurality of stator teeth formed radially on and integrally with an annular front face plate of said excavator body so as to cooperate with said rotor teeth. The stator teeth comprises plural groups of radially spaced apart tooth members having different length. Further, the tooth members comprises groups of comparatively long main tooth members and groups of comparatively short auxiliary tooth members each being disposed, respectively, between every adjacent two main tooth members.