How does the hydraulic system work

The teaching of hydraulics deals with the flow behavior of liquids. In technology and mechanical engineering, hydraulics is about the transmission of signals, forces and energy. Hydraulics is a branch of fluid technology. The word hydraulics comes from the Greek and can be derived from the combination of the two words hýdor "the water" and aulós "the pipe".
In this hydraulics script you can learn the basics of hydraulics and fluid technology.

Properties of hydraulic systems

A system is called a hydraulic system if it works according to the hydraulic principle.
As already described at the beginning of this hydraulics script, this means that forces, energy and signals are transmitted via a fluid. The fluids used for this are mineral oil, biodegradable fluids, flame-retardant fluids and water.

Hydraulic fluids

  • mineral oil
  • biodegradable liquids
  • hardly inflammable liquids
  • water

Forces that are transmitted in a hydraulic system are created by pressure. Movement is created by a volume flow. The transmitted power results from the factors pressure and volume flow.
The required pressure and volume flow in hydraulics is usually generated by a pump that is driven by an electric motor. In a hydraulic system, the hydraulic fluid always remains in the circuit (only in the case of water hydraulics it can be dispensed with). That means there is a return flow for the hydraulic fluid. For example, the hydraulic fluid can be conveyed to a consumer (e.g. hydraulic cylinder) by a pump and from there is returned to the fluid container via a return line.

In principle, the hydraulics work in the same way as the pneumatics. In pneumatics, however, compressed air is used to transmit power and signals, while in hydraulics it is liquids. In addition, there is no compressed air circuit in the pneumatics (there and back). The exhaust air is simply blown off into the environment (usually via a silencer). Advantages of hydraulics over pneumatics are that significantly higher forces can be transmitted and very precise and uniform movements can be implemented.

Construction of a hydraulic system

A system that works according to the hydraulic principle usually consists of a fluid container, a hydraulic pump, a consumer (hydraulic motor or hydraulic cylinder) that converts the hydraulic energy transferred by the pump into mechanical energy, and control elements (e.g. valves).

Areas of hydraulics

The hydraulics can be divided into the following areas:

  • Stationary hydraulics
  • Mobile hydraulics
  • Aircraft hydraulics
  • Vehicle hydraulics

Advantages and disadvantages of hydraulics

Hydraulic systems have the following advantages and disadvantages


  • Transmission of high forces and high performance with a small construction volume possible
  • Movements can also take place from a standstill under full load
  • Power and speed are infinitely variable
  • Protection against overload can be implemented easily and safely


  • The hydraulic system is limited by the temperature sensitivity of the fluid
  • High demands on the filtration of the hydraulic fluid
  • Risk of leaks
  • Compressibility of the liquid

Applications of hydraulics

Typical areas of application for hydraulics are hydraulic cylinders that are used in a wide variety of areas such as forklifts, excavators, lifting platforms, etc. Hydraulic systems can also be found in cars, airplanes for controlling the wing flaps and extending the landing gear, in cranes, machine tools and much more.