The hydraulic cylinder is a hydraulic actuator that converts hydraulic energy into mechanical energy and performs linear reciprocating motion (or swing motion). It has a simple structure and reliable work. When it is used to achieve reciprocating motion, the deceleration device can be eliminated, and there is no transmission gap, and the motion is stable. Therefore, it is widely used in various mechanical hydraulic systems. The output force of the hydraulic cylinder is proportional to the effective area of the piston and the pressure difference between its two sides: the hydraulic cylinder is basically composed of a cylinder barrel and a cylinder head, a piston and a piston rod, a sealing device, a buffer device and an exhaust device. According to the structure of commonly used hydraulic cylinders, it can be divided into four types: 1 piston type, 2-pillar type, 3 telescopic type, 4 swing type.

The working principle of each cylinder is almost the same. Take a manual jack as an example. The jack is actually the simplest oil cylinder. The hydraulic oil enters the oil cylinder through a one-way valve through a manual booster (hydraulic manual pump). At this time, the hydraulic oil entering the cylinder cannot be reversed again due to the single valve, forcing the cylinder rod upward, and then the work continues to make the hydraulic oil continue to enter the hydraulic cylinder, and it continues to rise. When it is about to fall, open the hydraulic valve to make The hydraulic oil returns to the oil tank. This is the simplest working principle. The others are improved on this basis. The principle of the cylinder is basically the same as that of the oil cylinder.