Hydraulics vs. pneumatics

Hydraulics vs. pneumatics ! Hydraulics and pneumatics

Hydraulics vs. pneumatics- Regardless of whether you are a hobby inventor and are planning a new project, have to prepare a lecture in physics or just want to know out of curiosity how hydraulic and pneumatic systems work and what the difference is – most of the questions in our community were on this topic already answered.

What are hydraulics and pneumatics and how do such systems work?

The terms hydraulics and pneumatics initially refer to the general theory of the flow or flow behavior of liquids (hydraulics) and gases (pneumatics). Liquids and gases are also called fluids as flowable substances , which is why hydraulics and pneumatics are summarized under the term fluid technology . From a technical point of view, it is always a matter of transferring a force and thus a movement from one place to another with the help of such a fluid. The force is generated by a pump or a compressor , regulated via control valves and transmitted via pipelines to a reciprocating piston or a rotating motor.
A special feature is that a form of the lever law also applies here. A piston with a small cross-sectional area in the pump can therefore transfer a multiple of the pump force to a larger working piston, which then only moves by a corresponding fraction of the distance that the pump piston has covered. As a result, very large forces can be generated even with relatively small pumps , because in this way they only have to pump faster but not more.

What is the difference between hydraulics and pneumatics? Or is it somehow the same?

Although the basic principle is the same for both methods ( Hydraulics vs. pneumatics ) , it makes a big difference whether you use a liquid such as oil or a gas such as air as the medium.

The reason for this is that gases – and thus also air – can be compressed in contrast to liquids. They are compressible while liquids are incompressible . A reciprocating piston filled with compressed air can still be compressed like a (more or less hard) spring, while a reciprocating piston filled with liquid remains virtually immobile regardless of the pressure.

But something else happens: when you compress a gas, it heats up pretty violently – and cools down just as quickly when the pressure drops, i.e. the gas expands . Incidentally, such an expansion can also happen suddenly and uncontrollably: Then one speaks of an explosion, which can have devastating effects at high pressures and large pressure vessels.

All of this has far-reaching consequences for the practical application of pneumatics: On the one hand, components in which gas is compressed can easily overheat and have to be cooled – on the other hand, components in which gas is expanded can ice up and become brittle. On the other hand, part of the energy used for compression is lost again as a result of the heating.

Now you already know some restrictions in the practical use of pneumatics. But is that why hydraulics are the superior technology? Time to compare . 

Hydraulics and pneumatics in comparison 

Here are the main differences between ( Hydraulics vs. pneumatics ) the two techniques for you:

Hydraulics

Advantages:

• Because liquids are practically incompressible, extremely high forces and a high level of precision of movement can be achieved.
• Even at extremely high pressure there is hardly any risk of explosion, since no pressure energy is stored in the liquid.

Disadvantage:

• Since water is corrosive and permanently attacks metal parts, expensive hydraulic oils or special water-based fluids usually have to be used.
• The oil circuit must be closed; return lines and filters are required for this.
• In the event of a leak, oil leaks and pollutes the environment (this is why, for example, vegetable oils must be used in forestry machines).
• Due to the higher frictional resistance of the liquid in the lines, no high flow velocities and therefore no very fast movements are possible.

Pneumatics

Advantages:

• Air is available everywhere, a closed circuit is not necessary.
• High flow velocities and therefore very fast movements are possible with air.
• Due to its compressibility, compressed air can also be stored in containers.
• Simple assembly, quick change of tools or motors, because the lines do not have to be refilled and vented.
• Air escaping in the event of a leak does not cause pollution.

Disadvantage:

• No extremely precise movements under load possible, as air “springs”.
• Very large cylinder surfaces are required for greater forces.
• High energy losses through heating and residual pressure of the “used” compressed air.
• Risk of explosion at high pressure.

So you see that both techniques ( Hydraulics vs. pneumatics ) can do something that the other cannot. Wherever high speeds with little or medium force are required, pneumatics are the right choice, for high forces with low speeds, hydraulics. You can imagine this particularly well if you, for example, compare an air rifle with a hydraulic scrap press – two completely different applications, each of which could not work with the other technology.