SWELLING COMPENSATOR

PURPOSE:To made the efficiency of operations higher by a method in which a cylinder to give pulling force of drag head and an accumulator are connected through a working fluid, and a piston serving as one partition wall of the accumulator is moved and fixed by an actuator. CONSTITUTION:An open air discharge valve 28 is closed, and an air supply valve 26 is opened to supply compressed air to an accumulator chamber 25. A given pushing-up force is given to a cylinder 8, and a ground contact pressure is set up. An optimum spring constant is selected for the soil to be dredged. A solenoid valve 29 is operated, the position of the piston 22 is decided by an oil-pressure cylinder 20, and the volume of the accumulator chamber 25 is matched with the spring constant. The air supply valve 26 is closed, the cylinder 20 is locked by the solenoid valve 29, and the setting of the ground contact pressure and spring constant is completed. Since the volume of the chamber 25 can be optionally varied by the cylinder 20, optimum ground contact pressure and optimum spring constant corresponding to the quality of the soil to be dredged can be selected.