The hydraulic cylinder is the hydraulic actuator that changes the hydraulic energy into mechanical energy and does reciprocating motion (or oscillating motion) in a straight line.It is simple in structure and reliable in operation.When it is used to realize reciprocating motion, the deceleration device can be removed, and there is no transmission gap, the motion is stable, so it is widely used in all kinds of mechanical hydraulic system. The output force of the hydraulic cylinder is proportional to the effective area of the piston and the pressure difference on both sides.The hydraulic cylinder is basically composed of cylinder barrel and cylinder head, piston and piston rod, sealing device, buffer device and exhaust device.Buffering devices and exhaust devices depend on the specific application; other devices are essential. Hydraulic drives have cylinders and motors that convert the pressure energy of a liquid into mechanical energy and output it.Cylinder is mainly output linear motion and force. Hydraulic cylinder has a variety of forms, according to the different characteristics of its mechanism it can be divided into piston type, plunger type and swing type three categories, according to the mode of action it can be divided into single action and double action. Piston cylinder, plunger cylinder is mainly used in: machinery, such as excavator;Scientific research, such as university structural laboratory. The oscillating hydraulic cylinder is an actuator which can output torque and realize reciprocating motion. It has several forms such as single vane, double vane and spiral oscillation.Blade mode: the stator block is fixed to the cylinder block, and the blade is connected to the rotor.According to the direction of oil intake, the blades will drive the rotor to oscillate back and forth.Spiral swing type is divided into single spiral swing and double helix two kinds, now double helix is more commonly used, by the two spiral sidelobe piston in the hydraulic cylinder straight motion into linear motion and rotation motion composite motion, so as to achieve the swing motion. Buffer device In the hydraulic system, the use of hydraulic cylinder to drive a mechanism with a certain mass, when the hydraulic cylinder movement to the end of the stroke has a greater kinetic energy, such as not decelerated processing, the cylinder piston and cylinder head will occur mechanical collision, impact, noise, destructive.In order to mitigate and prevent the occurrence of this kind of harm, therefore can set up in the hydraulic loop deceleration device or set up in the cylinder block buffer device.