Rotary hydraulic cylinder that performs rotational motion, unlike linear motion cylinders, this is a special hydraulic actuator where the piston rod performs reciprocating motion while rotating. Used in manufacturing processes requiring simultaneous rotation and linear motion such as workpiece rotation in machine tools, part inversion in automation equipment, and product orientation changes on assembly lines. Applied in NC lathe chuck drives, injection molding machine mold rotation mechanisms, and press machine workpiece positioning, enabling complex operations impossible with conventional hydraulic cylinders. Available in vane type, pinion rack type, and spiral type structures, selected based on rotation angle and torque specifications.