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Selecting the right seals for rotating shafts: comparison, table and practical decision-making aid for industrial applications.
Seals for rotating applications perform a central function in machines and systems. The right choice depends essentially on three factors: speed, pressure and medium. These determine whether a radial shaft seal, a mechanical seal or a non-contact solution is the appropriate choice. They ensure that media such as oil, water or chemical substances are reliably kept inside the system while at the same time no contaminants can penetrate. In doing so, dynamic loads act continuously on the seal: rotating movements, friction between the components as well as temperature and pressure fluctuations.
In contrast to static seals, rotation places significantly higher demands on material, design and dimensioning. Even small deviations in selection lead to increased wear, rising friction or unwanted leakage. In practice, it is often evident that the service life of an entire assembly depends directly on the quality and fit accuracy of the seal used.
A well-founded selection is therefore always based on a clear understanding of the operating conditions and the appropriate sealing technology. Only in this way can failures be reduced, maintenance intervals extended and operating costs sustainably lowered.
What requirements arise with rotating seals
In rotating applications, several factors act simultaneously:
- Shaft speed
- Pressure in the system
- Temperature
- Type of medium (oil, water, chemicals)
- Friction and lubrication
The higher the speed, the more friction and heat generation increase. This has a direct influence on the service life of the seal.
The most important seal types at a glance
Radial shaft seal
The radial shaft seal is one of the most frequently used seals in mechanical engineering and forms the standard solution in many applications. Further details and variants can be found on our page on radial shaft seals. It rests with an elastic sealing lip directly against the rotating shaft and thus ensures reliable sealing against liquids such as oil or grease. Thanks to its compact design, it can be integrated in a space-saving manner and offers a good ratio of cost to performance.
In applications with medium speeds and stable operating conditions, this seal type shows high reliability. Limits arise above all at very high speeds or strongly fluctuating temperatures, as friction and wear increase significantly here.
Mechanical seal
Mechanical seals are used in applications where higher demands are placed on pressure resistance and media compatibility. An overview of designs can be found under mechanical seals. Two precisely manufactured sealing surfaces slide against each other and thus form a very tight and controlled seal.
This design enables use in demanding environments, for example in pumps or systems with aggressive media. At the same time, it requires exact dimensioning and stable operation, as even small deviations can affect the sealing effect.
Labyrinth seal
Labyrinth seals work without direct contact between the components and instead use a targeted deflection of the medium through a complex geometry. Information on areas of application can be found under labyrinth seals. This creates a seal with very low wear, as no classic friction takes place between seal and shaft.
This property makes them particularly suitable for applications with very high speeds or long running times. At the same time, the sealing effect depends heavily on the design and the operating conditions, so they are used above all in specialised applications.
Materials for rotating seals
The choice of material directly influences performance. Frequently used materials:
| Material | Properties | Application |
|---|---|---|
| NBR | good oil resistance | standard applications |
| FKM | high temperature resistance | chemically stressed systems |
| PTFE | low friction | high speeds |
| EPDM | resistant to water and steam | sanitary and water technology |
The combination of material and application decisively determines the service life.
Technical fundamentals and limit ranges
In practice, rotating seals are often assessed via peripheral speeds. Low ranges are usually below 5 m/s, medium applications are between 5 and 15 m/s, while high speeds go beyond this.
Temperature ranges also play a central role. NBR is often used up to about 100 °C, FKM covers significantly higher ranges and is suitable for thermally stressed applications. PTFE offers advantages at high speeds thanks to very low friction values.
These technical framework conditions form the basis for any well-founded selection.
Key selection criteria
For the right selection, the following points should be checked:
- Speed range of the shaft
- Pressure conditions
- Temperature range
- Lubrication state
- Media resistance
- Installation space and geometry
In addition, technical details play a major role. The surface quality of the shaft directly influences the wear of the sealing lip. Too rough a surface increases friction, too smooth a surface can lead to insufficient lubricating film formation.
Typical limit ranges should also be taken into account. Elastomer seals such as NBR often operate in the temperature range up to about 100 °C, while FKM covers significantly higher temperatures. PTFE shows advantages at very high speeds thanks to low friction values.
The more precisely the operating conditions are known, the more precisely the appropriate seal can be selected.
Influence of installation and operation
Installation has a direct influence on the function of the seal. Clean assembly, correct alignment of the shaft and suitable lubrication during installation contribute significantly to the service life.
During operation, too, factors such as shaft run, vibrations and temperature development act on the seal. Even small deviations lead to uneven loading and accelerated wear.
Typical errors in selection
An additional critical point lies in installation and assembly. Even small deviations in the alignment of the shaft or unclean assembly lead to uneven loading of the seal. Missing or incorrect lubrication during installation can also lead to immediate wear.
In practice, similar problems occur again and again:
- wrong material for the medium
- insufficient temperature resistance
- failure to take speed into account
- wrong dimensioning
A frequent practical error shows up in applications with increasing speed. If a classic radial shaft seal continues to be used here, friction rises sharply and leads to rapid heating. The result is hardened sealing lips and premature failure.
Another typical scenario concerns aggressive media. If an unsuitable material is chosen, the seal swells or loses its mechanical properties. As a result, the sealing effect drops significantly.
These errors frequently lead to premature wear or leaks.
Practical examples of applications
Rotating seals are used in numerous areas. In practice, typical problems with clear solutions emerge.
In pump shafts, leakage through pressure and medium frequently occurs. A mechanical seal is suitable here, as it enables stable sealing even with demanding media.
In gearboxes with medium speeds and oil-lubricated systems, a radial shaft seal is usually used. This solution offers economical and reliable sealing.
At very high speeds, for example in fans or turbines, high friction quickly arises. In such cases, labyrinth seals or PTFE-based solutions offer clear advantages thanks to low wear.
Depending on the application, the requirements vary considerably.
Standard solution or custom-made part
Standard seals cover a large proportion of typical applications and offer an economical and quickly available solution. In many cases, they reliably meet the requirements, provided the operating conditions lie within the intended limits.
In practice, however, it often becomes evident that standard solutions reach their limits as soon as several influencing factors act simultaneously. Combinations of high speed, temperature and aggressive media quickly lead to increased wear or unstable sealing conditions.
Custom-made parts start at exactly this point. Individual solutions can be found under seals to measure. They enable exact matching of geometry, material and sealing principle to the specific application. As a result, friction can be reduced, service lives extended and maintenance effort lowered. Especially in industrial applications with high loads, this creates a clear economic advantage.
Quick decision overview
| Speed | Pressure | Medium | Recommended seal |
|---|---|---|---|
| low to medium | low to medium | oil / grease | radial shaft seal |
| medium to high | high | aggressive media | mechanical seal |
| very high | low | air / low media load | labyrinth seal / PTFE |
This overview enables a quick pre-selection based on the most important influencing factors.
Comparison: which seal fits when?
The radial shaft seal is suitable for classic applications with moderate conditions and offers an economical solution for many standard cases.
The mechanical seal shows its strength in demanding environments with pressure and critical media, where stable and long-lasting sealing is required.
The labyrinth seal plays out its advantages at very high speeds, as it works without direct contact and therefore generates hardly any wear.
Selection in practice: concrete decision-making aid
The selection of a seal for rotating applications can be clearly structured in practice.
At high speeds, the focus is on low-friction systems. PTFE seals or labyrinth seals are suitable here.
At high pressures or with critical media, a mechanical seal offers the necessary stability.
For classic applications in mechanical engineering with moderate conditions, the radial shaft seal represents a proven solution.
In addition, it should always be checked which material suits the application. For oil-containing media, NBR is suitable, while FKM is used at high temperatures.
The selection is therefore based on a few clear parameters that can be assessed systematically. For concrete projects, a direct enquiry to agree the appropriate solution is recommended. Companies that take these factors into account properly increase operational safety and significantly extend the service life of their systems.
FAQ
Which seal is suitable for rotating applications?
The selection depends on speed, pressure and medium. Radial shaft seals are suitable for standard applications, mechanical seals for high pressures and labyrinth or PTFE seals for very high speeds.
When is a radial shaft seal the right choice?
Radial shaft seals are suitable for oil- or grease-lubricated systems with moderate speeds and stable operating conditions in mechanical engineering.
Which seal is suitable for high speeds?
For high speeds, low-friction solutions such as PTFE seals or non-contact labyrinth seals are suitable, as they reduce wear and heat generation.
When is a mechanical seal used?
Mechanical seals are used at high pressures, with critical media and in demanding applications such as pumps or chemical systems.
What role does the material play?
The material determines resistance, temperature behaviour and service life. NBR is suitable for oil, FKM for high temperatures and PTFE for low-friction high-speed applications.
Why do rotating seals fail prematurely?
Typical causes are the wrong choice of material, insufficient lubrication, faulty assembly or dimensioning that does not suit the speed and temperature.
When is a custom-made seal worthwhile?
An individual solution is worthwhile for high loads, special geometries or demanding media, where standard seals reach their limits.
Our rubber sheets
For industry and trade, we offer a wide variety of rubber sheets.
SBR rubber sheet
Our high-quality SBR rubber sheet (styrene-butadiene rubber) is the solution for numerous industrial and commercial applications. This rubber sheet is manufactured from first-class styrene-butadiene rubber and is characterised by its outstanding physical properties.
EPDM rubber sheet
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NBR rubber sheet
The NBR rubber sheet is a high-quality industrial product that has been specially developed for applications where excellent resistance to oils, greases and various chemicals is required.
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FKM rubber sheet
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Silicone rubber sheet
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