What is the working principle of a hydraulic cylinder?

In today’s highly mechanized world, an increasing share of hydraulic cylinder‑driven tasks is performed by machinery. Humans can no longer do without them. With the aid of machines, we are able to accomplish these jobs. It is precisely thanks to hydraulic cylinders that our lives have become more convenient and that societal development has progressed so rapidly. To keep pace with societal progress and boost operational efficiency, hydraulic‑cylinder‑based equipment has grown larger and more efficient. These large‑scale machines can perform their duties effectively only because of their core component—the hydraulic cylinder. Many heavy‑duty machines rely on hydraulic cylinders as the central means of power transmission; it is solely through hydraulic cylinders that they can carry out such tasks.

What is the working principle of a hydraulic cylinder?

Hydraulic cylinders are hydraulic devices that convert hydraulic energy into mechanical energy, producing linear reciprocating or oscillating motion. With their simple structure and stable reciprocating performance, they are widely used in various types of construction machinery, marine vessels, machine tools, and even defense‑related equipment.

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

Classification of Hydraulic Cylinders

Hydraulic cylinders come in two types: single‑rod cylinders and double‑rod cylinders. A single‑rod hydraulic cylinder has a piston rod on only one end, with oil outlets and return ports at both ends, enabling bidirectional motion; it is also referred to as a double‑acting cylinder. Hydraulic cylinders are commonly used in construction machinery such as hydraulic excavators.

Since the piston rods on both sides of the hydraulic cylinder have the same diameter, the effective working areas at both ends of the piston are identical. If hydraulic fluid at the same pressure and flow rate is supplied to both the left and right chambers, the piston will generate equal thrust and reciprocate at the same speed. Such hydraulic cylinders are commonly used in applications where a constant reciprocating speed is required but relatively low thrust is sufficient, such as in the worktable of a grinding machine.

Solutions for Hydraulic Cylinder Operating Noise

1) The cylinder’s filter is clogged with contaminants and cannot filter the oil: Remove the contaminants from the filter using clean hydraulic fluid.

2) Insufficient oil level, excessively high suction position, or the suction pipe exposed above the oil level: Add oil to the specified level and lower the suction position.

3) There are no paper gaskets on either side of the pump body and pump cover; the pump body and pump cover are not sealed perpendicularly, resulting in air ingress during rotation. Install paper gaskets between the pump body and pump cover, and grind the pump body on a flat plate using emery cloth to ensure that the perpendicularity error between the pump body and pump cover is less than 0.005 mm. Secure the connection between the pump body and pump cover tightly, ensuring there are no leaks.

4) The cylinder drive shaft and the motor coupling are misaligned, resulting in torsional friction: Adjust the concentricity of the pump–motor coupling so that the deviation does not exceed 0.2 mm.

5) Insufficient gear meshing accuracy of the hydraulic cylinder: grind the gears to achieve proper gear meshing.

6) The oil seal skeleton on the cylinder shaft has come loose, and the pump housing is not sealed: Replace with a qualified pump shaft oil seal.