Hydraulic cylinder is an actuator in hydraulic transmission, which converts hydraulic energy of hydraulic oil into machinery. Hydraulic cylinder consists of cylinder block, end cap, piston, piston rod, hanger and other parts. According to the direction of action of pressure oil in hydraulic cylinder, it can be divided into two types: single-acting hydraulic cylinder and double-acting hydraulic cylinder. Single-acting hydraulic cylinder is usually plunger or sleeve, or piston-acting hydraulic cylinder. Two oil chambers can enter and exit pressure oil.