Limiting and unloading hydraulic clamping device

The utility model relates to a limiting and unloading hydraulic clamping device. The device comprises a piston, a cylinder body and a supporting sleeve, wherein a step-shaped pipe wall is formed on the front outer wall of the piston, an oil pipe port channel is axially formed on the inner wall of the piston and extends out of a step-shaped wall surface, the cylinder body is coaxially sleeved outside the piston, the rear inner wall of the cylinder body is provided with a step-shaped pipe wall which is closely fit with the piston, an oil drainage through hole is formed in the pipe wall of the cylinder body in a distance of Lmax (maximum limiting displacement) from the step surface of the piston, a limiting valve is assembled in the through hole and consists of a ball valve plug, a spring and an adjusting screw, and a damping hole is formed in the adjusting screw of the limiting valve and communicated the outside of the clamping device. In practical work, after high pressure oil is filled into the clamping devic