In today’s highly mechanized world, an increasing number of tasks are performed by machines. Humans can no longer do without them. Machines enable us to accomplish work efficiently—indeed, they are indispensable. Our lives have become far more convenient, and the rapid pace of social development is also thanks to their contributions.

To keep pace with societal development and enhance operational efficiency, machinery is becoming increasingly large and efficient. These machines can perform their tasks effectively only with the aid of a key component: hydraulic cylinders. Many heavy-duty machines rely on hydraulic cylinders as the core mechanism for force transmission, enabling them to accomplish their intended functions.

Hydraulic cylinders are hydraulic devices that convert hydraulic energy into mechanical energy, enabling linear reciprocating or oscillating motion. They feature a relatively simple structure and provide smooth, reliable operation during reciprocation, making them widely used in various types of construction machinery, marine vessels, industrial equipment, and even defense systems.

In the 17th century, Pascal’s principle of hydrostatic pressure transmission laid the foundation for the subsequent development of hydraulic cylinders.

In 1795, the British used water as a working fluid and applied hydraulic presses in industry, giving rise to the world’s first hydraulic press.

In 1905, the working fluid was changed to oil, further enhancing performance.

Following World War I, humanity entered the industrial era, and hydraulic transmission began to be widely adopted.

Different machines require different types of hydraulic cylinders. Based on their structural design, hydraulic cylinders are primarily classified into piston cylinders, plunger cylinders, and oscillating cylinders, each serving distinct functions.

Piston hydraulic cylinders are classified as single-piston and double-piston types. A single-piston hydraulic cylinder has a piston rod extending from only one end. Both ends are equipped with an outlet and a return port, enabling bidirectional motion. Also known as double-acting cylinders, they are commonly used in construction machinery such as hydraulic excavators.

Double-rod hydraulic cylinders have piston rods extending from both ends, and their configuration is essentially the same as that of single-rod hydraulic cylinders. When oil enters the right chamber and exits the left chamber, the piston moves to the left; conversely, when oil enters the left chamber and exits the right chamber, the piston moves to the right.

Since the piston rod diameter is the same, the effective cross-sectional area on both sides of the piston is identical. If equal pressures and hydraulic fluid are applied to the left and right ends, the piston will generate the same thrust and reciprocating speed. This type of hydraulic cylinder is typically used in applications where the reciprocating speed must be consistent but the required force is relatively low, such as in grinding‑machine tables.

A plunger hydraulic cylinder is a single‑acting cylinder that can move in only one direction, driven by fluid pressure. The plunger does not contact the cylinder wall under any external forces or its own weight. Pressure is applied at the plunger’s end; to ensure sufficient thrust and stability, the plunger is typically relatively thick and heavy. Horizontal installation can lead to uneven wear, so such cylinders should be mounted vertically on machines with long strokes.

The hydraulic cylinder’s piston rod features two check valves: when the piston moves in one direction, a vacuum is created inside the cylinder. This causes the first check valve to open, allowing fluid to enter the cylinder; as the piston shifts in the opposite direction, it compresses the fluid, triggering the second check valve to open and expel the fluid drawn into the cylinder. This operating principle ensures a continuous fuel supply during sustained motion.