Earth discharge control system for small-diameter pipe propelling machine

A pipe propelling machine for positioning a small-diameter pipe in the ground, the small-diameter pipe having a front end, the pipe propelling machine comprising:

• a leading pipe positioned against the front end of the small-diameter pipe, the leading pipe having a front end that is positioned forward of the front end of the small-diameter pipe;
• a propelling unit for moving the small-diameter pipe and the leading pipe forward;
• a screw conveyor disposed in the leading pipe for transporting earth rearwardly from the front end of the leading pipe, said screw conveyor including a rotatably mounted screw shaft and a drive unit connected to the screw shaft for rotating the screw shaft, said drive unit being configured to rotate the screw shaft at a variable screw shaft speed;
• and a pneumatically operated control valve located within the leading pipe, said control valve including a valve element for regulating movement of earth along the screw conveyor, said valve element having an expandable pressure chamber that is inflated to a set pressure;
• comprising the improvement wherein a control system is provided for regulating the discharge of earth from the leading pipe, said control system including:
• a pressure detector in fluid communication with the pressure chamber for monitoring the pressure of the pressure chamber and being configured to generate a pressure-sensed signal representative of the pressure in the pressure chamber;
• and
• processor means connected to said pressure detector for receiving the pressure-sensed signal and connected to the drive unit for controlling the drive unit so as to regulate the screw shaft speed, said processor means being configured to calculate a pressure difference between the set pressure of the pressure chamber and the actual pressure of the pressure chamber as indicated by the pressure-sensed signal and to control the drive unit so as to regulate the screw shaft speed based on the calculated pressure difference.