Hydraulic system: design & applications explained simply

A hydraulic system is used to apply large forces in a targeted manner over a defined distance with minimal effort. The underlying hydraulic principle is simple, but it requires particularly high-quality materials. If correctly designed and well maintained, a hydraulic system can operate reliably for many years.

The hydraulic principle is also used in hydraulic systems

The hydraulic principle is based on the law of nature that liquids are not compressible. This means that applied pressure is transmitted to any point within the hydraulic system with virtually no loss. This can be used to generate large forces.

The simplest hydraulic system consists of two hydraulic cylinders connected by an oil line. When a piston moves into its cylinder, the piston in the connected cylinder moves out—and vice versa. If both pistons have the same effective area, the force, speed and travel of the extending and retracting piston are the same. It becomes interesting when the cross-sections of the effective areas of the two pistons differ. The change in force and speed is proportional to the size ratio of the effective areas. This is why the smaller piston can be retracted with little force, while the large piston extends with a much greater force, as in a car jack, for example.

The components of a hydraulic system

Hydraulic systems consist of at least the following components:

• Pressure source or pump
• Closed piping system
• Tank
• Actuator

Actuators are the modules that are moved by hydraulic pressure. A distinction is made between linear and radial motors.

Depending on the size and range of tasks the hydraulic system is intended to perform, the number of its components increases. Additional components may therefore include the following:

• Valves
• Sensors
• Cooler
• Filter

Valves control the volumetric flow in the lines. Sensors monitor the condition of the hydraulic system. Coolers protect the oil from overheating. Filters retain suspended particles and thus prevent internal damage to the hydraulic system.

Applications of a hydraulic system

Hydraulic systems are used wherever high forces need to be applied flexibly, in a targeted manner, and with minimal effort. Competing systems include levers, block and tackle systems, electromagnetic actuators, or pneumatic systems. Disadvantages of a hydraulic system are the high cost of its components, the high maintenance requirements, and severe contamination in the event of a leak. In addition, hydraulic systems operate very slowly. However, they also offer major advantages. Thanks to the flexible arrangement of their components and lines, they can be used in a particularly versatile manner. Using hoses instead of rigid lines also makes the hydraulic system capable of motion. This is especially evident in mobile equipment such as excavators, forklifts, or loaders. Above a certain force requirement, the hydraulic system is the only way to meet that demand. This makes this technology an indispensable part of engineering in the future as well.