Plastics in hydraulics and pneumatics
Which plastics are used in hydraulic and pneumatic systems. Comparison of PA, POM, PTFE, PU, PE and PEEK.
Hydraulic and pneumatic systems form the backbone of numerous industrial applications – from production machinery through mobile work equipment to precision controls. The systems must operate reliably under high pressure, changing temperatures and sometimes aggressive media. While metals were long the first choice, plastics have been gaining in importance for decades.
The reason lies in their specific advantages: low weight, easy processing, high corrosion resistance and diverse possibilities for adapting the properties through additives or fibre reinforcement. Nevertheless, the choice of material remains complex, since every application places its own requirements. This article sheds light on the most important plastics in hydraulics and pneumatics, their properties, areas of application, limits and future trends.
Fundamentals: requirements for materials in hydraulics and pneumatics
The requirements for plastics in hydraulic and pneumatic systems are multi-layered. Mechanical load-bearing capacity plays a central role, since components such as valve bodies, seals or gears must withstand high forces and pressure peaks. The materials must remain dimensionally stable over the long term in order to prevent leaks and system failures.
In addition, chemical resistance is decisive, because hydraulic oils, compressed air with oil content, coolants or aggressive cleaning agents must not attack the surface. A further factor is the friction and wear properties: many components are in motion, which is why low coefficients of friction and high abrasion resistance are essential in order to ensure energy efficiency and extend maintenance intervals.
Finally, temperature and ageing resistance must also be taken into account. Depending on the ambient temperature and the operating conditions, plastics must withstand both cold and heat without losing their properties.
Important plastics in use
Polyamide (PA)
Polyamide is frequently used for hoses, valve bodies and housings. It impresses with good strength, abrasion resistance and an attractive price-performance ratio. PA is particularly widespread in pneumatics, since it offers a good balance between rigidity and flexibility. However, PA tends to absorb moisture, which can affect dimensional accuracy.
For precise applications or for use in damp environments, modified PA types or special additives must therefore often be used. Glass fibre reinforcement can significantly improve stability, making PA competitive even in highly loaded applications.
Polyoxymethylene (POM)
POM is known for its high dimensional accuracy, rigidity and excellent sliding properties. It is particularly suitable for gears, guides, valve bodies and precision parts that must maintain a constant shape even under continuous load.
POM is also characterised by good resistance to many solvents, lubricants and weak acids. In hydraulic systems it is frequently used when metallic components are to be replaced by a lighter material without having to compromise on precision. Limitations exist at temperatures above 100 °C, since POM loses stability here.
Polyethylene (PE)
Polyethylene is a versatile material that stands out through high chemical resistance, low weight and good machinability. In pneumatic systems, PE is used above all for hoses and lines, since it is very flexible and easy to install.
It is used in particular where aggressive media such as alkalis or acids are transported. However, PE quickly reaches its limits at higher temperatures and pressure loads. It is therefore more suitable for applications with moderate operating conditions and is frequently used as a cost-effective solution.
Polytetrafluoroethylene (PTFE)
PTFE is regarded as a classic among high-performance plastics. It stands out through extremely low coefficients of friction, very good non-stick properties and virtually universal chemical resistance. PTFE withstands temperatures of up to 260 °C and remains flexible even at low sub-zero temperatures. It is used above all for seals, bearings, guide rings and valve seats, where low friction and resistance to aggressive media are required.
However, PTFE exhibits comparatively low mechanical load-bearing capacity, which is why it often has to be supplemented with fillers or metallic reinforcements in order to extend its service life.
Polyurethane (PU)
PU is one of the most frequently used plastics for hoses in pneumatic systems. It combines high flexibility with good abrasion resistance and pressure resistance. This makes it ideal for applications with frequent movement cycles in which material fatigue must be avoided. PU hoses are more resistant than many alternatives made of PE or PVC and can nevertheless be installed easily.
Disadvantages exist above all in contact with strongly aggressive chemicals or solvents, which can shorten the service life. Special formulations can partially compensate for these weaknesses.
Polyetheretherketone (PEEK)
PEEK is one of the high-performance plastics and is used where standard materials are no longer sufficient. It combines extreme mechanical strength with high chemical resistance and temperature resistance up to 250 °C. PEEK is used for valve seats, seals, high-pressure bearings and complex precision parts that must function reliably under continuous load.
Although PEEK is very expensive compared with other plastics, its exceptional performance justifies its use in critical applications in which failures must be avoided. In addition, PEEK is increasingly used in combination with fibre reinforcements in order to achieve even higher stability.
Other plastics
Alongside the plastics mentioned, glass fibre or carbon fibre reinforced variants, fluoroplastics such as FEP or ETFE as well as high-performance polymers such as PPS are also gaining in importance.
These materials expand the range of applications, particularly under extreme conditions, and are an important component of future developments.
Comparison of properties
| Plastic | Mechanical strength | Chemical resistance | Temperature resistance | Typical applications |
|---|---|---|---|---|
| PA | high | medium | medium | hoses, housings, valves |
| POM | high | high | medium | gears, guides, precision parts |
| PE | medium | high | low | hoses, lines |
| PTFE | low | very high | very high | seals, bearings, guides |
| PU | medium | medium | medium | hoses, lines, protective elements |
| PEEK | very high | very high | very high | valve seats, seals, high-load parts |
Practical examples from industry
- Pneumatic cylinders: guide rings made of PTFE reduce friction and increase the service life.
- Hydraulic valves: valve seats made of PEEK ensure high tightness even under continuous load.
- Control lines: flexible PU hoses facilitate installation and withstand high movement cycles.
- Seals: PTFE seals prevent leaks in oil-containing systems.
Challenges and limits
Despite numerous advantages, the use of plastics remains associated with limitations. Extreme pressure peaks can lead to cracking or material failure. Temperature ageing also reduces the service life of some polymers.
For applications with very high safety requirements, a combination of metal and plastic components is therefore often the best solution. In addition, the processing of high-performance plastics such as PEEK or PTFE requires special know-how and adapted manufacturing techniques.
Future trends
The further development of plastics for hydraulic and pneumatic systems is moving in several directions. The focus is particularly on fibre-reinforced plastics, which considerably increase mechanical strength and thus enable use even in heavily loaded components.
At the same time, hybrid materials are gaining in importance, combining the advantages of metals and polymers in a single component and thereby offering new possibilities with regard to weight, strength and costs. The aspect of sustainability is also becoming increasingly important. Manufacturers are working more intensively on bio-based plastics and recycling solutions in order to improve the ecological balance of the systems.
In parallel, materials are being developed that offer a longer service life and thereby reduce maintenance effort. In sum, the role of plastics in hydraulics and pneumatics will continue to grow, since they increasingly meet the rising requirements for efficiency, durability and sustainability.
In conclusion
Plastics have developed in hydraulic and pneumatic systems from niche materials into indispensable materials. Standard polymers such as PA, POM or PU secure the basis, while high-performance plastics, such as PTFE and PEEK, enable demanding applications. Careful material selection, matched to pressure, temperature, medium and expected service life, remains decisive. In addition, it is necessary to keep an eye on the total costs: although high-performance polymers are more expensive, they can offer cost advantages over the entire life cycle through a longer service life and lower maintenance effort.
With advancing material development, the role of plastics will continue to grow – towards more powerful, more sustainable and even more versatile solutions that do not replace metals but sensibly complement them. In this way, plastics make an important contribution to increasing efficiency, reducing costs and conserving resources in industry.
Frequently asked questions
Which plastics are suitable for seals in hydraulic systems? PTFE and PEEK are particularly suitable, since they are both chemically and thermally very stable.
Are plastic hoses in pneumatics durable? Yes, PU and PA hoses in particular stand out through high abrasion resistance and a long service life, as long as they are operated within the specified conditions.
Why are not all metal parts replaced by plastics? Metals remain superior in extreme high-pressure and high-temperature applications. Plastics complement these through flexibility, weight reduction and chemical resistance.
What role do fibre-reinforced plastics play? They combine the advantages of lightweight plastics with significantly increased mechanical strength and will be used more frequently in hydraulic and pneumatic systems in future.
What advantages do plastics offer compared with metals in processing? Plastics can be moulded, milled and extruded more easily, whereby complex geometries can be produced more economically.
What typical mistakes can occur in material selection? Plastics are frequently used that do not permanently withstand the temperature or pressure requirements. Insufficient media resistance can also lead to premature failure.
How do additives and fillers influence the properties of plastics? Properties can be specifically improved through additives such as glass fibres, lubricants or stabilisers. They increase strength, reduce friction or extend the service life, but must be carefully matched to the intended use.
