An O-ring, also known as a rubber sealing ring, O-ring seal or sealing ring, is one of the most widely used seals in engineering. O-rings are used to seal liquids and gases in hydraulic and pneumatic systems, pumps, valves, compressors and machinery. Due to their simple shape, O-rings are relatively easy to manufacture, install and replace. However, selecting the correct O-ring is important.
Material, size, hardness, temperature, pressure and the medium with which the seal comes into contact together determine whether an O-ring is suitable for an application.
Techniparts supplies O-rings in a wide range of materials, sizes and designs. These include metric dimensions, inch sizes and AS568 dimensions. Various elastomers are also available, including NBR, EPDM, FKM, FVMQ, VMQ, HNBR, ACM, FFKM, IIR, CR and AU. Do you need a specific size or material? Use our O-ring search engine to easily find the right O-ring. You can also contact us for technical advice on selecting the correct seal.
An O-ring is a ring-shaped seal with a circular cross-section. The seal is installed in a specially designed groove and then enclosed between two components. When the components are pressed together, the elastomeric material of the O-ring is deformed. This creates sealing contact between the O-ring and the surrounding surfaces. As system pressure increases, the seal can also be pressed more firmly against the sealing surfaces.
This can provide an effective seal at both low and relatively high pressures, provided that the size, material and construction have been selected correctly. O-rings are used for both static and dynamic applications. In a static application, the sealing components do not move relative to each other. In a dynamic application, movement does occur, for example in a hydraulic cylinder.
The operating conditions therefore determine which design is most suitable.
O-rings are used in a wide variety of technical systems. In hydraulic installations, for example, they are used to seal connections, valves, cylinders and other components. In pneumatic systems, they provide reliable sealing of air and other gases. This type of seal is also common in pumps, compressors, couplings, machinery and industrial installations.
The popularity of O-rings is partly due to their simple construction, the wide range of materials and the availability of many different sizes. For reliable operation, however, the conditions under which the seal is used must always be considered. An O-ring that is highly suitable for water, for example, may be unsuitable for certain oils or chemicals. Temperature, pressure, movement and groove dimensions also play an important role in the selection.
With a static seal, the components between which the O-ring is installed remain in the same position relative to each other. Examples include flange connections, covers, couplings and other fixed connections. With dynamic seals, one component moves relative to the seal. This can be a reciprocating movement, as in a cylinder, or a rotating movement.
Dynamic applications place greater demands on the material, lubrication, surface quality and the groove in which the O-ring is installed. Not every material and hardness is therefore suitable for every type of movement. The correct combination of material, dimensions, hardness and construction is important to prevent leakage and premature wear.
The size of an O-ring is generally determined by its inside diameter (ID) and cross-section (CS). The inside diameter is the diameter measured on the inside of the ring. The cross-section is the thickness of the round material from which the seal is made. These two dimensions determine the size of an O-ring. The outside diameter can then be calculated from the inside diameter and cross-section.
When replacing an existing seal, it is important not to look only at the outside diameter. Even a small difference in inside diameter or cross-section can affect the fit, compression and therefore the performance of the seal. To determine the correct size, you can use our O-ring calculation tool.
In addition to metric sizes, many O-rings are available according to international and industrial size standards. Metric dimensions are generally specified in millimetres. Inch versions use inch dimensions. Another common standard is AS568, which is mainly used in applications based on American dimensions. DIN and ISO dimensions are also available.
When ordering, it is therefore important not to rely solely on a description such as "O-ring 20 mm", but to always check exactly which dimension is meant. A dimension can refer to the inside diameter, outside diameter or cross-section. If you are unsure, we can help determine the correct size using existing components, drawings or technical specifications.
A designation such as 20 x 2.5 mm generally refers to an O-ring with an inside diameter of 20 mm and a cross-section of 2.5 mm. The resulting outside diameter depends on these two values. For technical applications, it must then be checked whether this dimension fits the available groove. The groove dimensions determine how much the seal is compressed and how much space is available for possible expansion of the material.
The pressure and movement of the application also play a role. An O-ring with the correct nominal size is therefore not automatically suitable for every application. In addition to the dimensions, the material, hardness and operating conditions must always be considered.
The material of an O-ring largely determines which liquids, gases, temperatures and operating conditions the seal can withstand. There is therefore no single material that is suitable for every application. Common materials include NBR, FKM, EPDM, HNBR, VMQ, FVMQ, ACM, FFKM, IIR, CR and AU. Each elastomer has its own properties.
NBR is widely used with mineral oils and certain fuels, while EPDM is known for its properties with water, hot water, steam and weathering. FKM is often selected when higher temperature and chemical resistance are required. High-performance materials such as FFKM are available for particularly demanding chemical applications. View the overview of O-ring materials for more information about the different compounds.
NBR, also known as nitrile rubber or Buna-N, is a widely used sealing material. The properties of NBR are influenced, among other factors, by the acrylonitrile content of the material. As a result, different compounds are available with different properties in terms of oil and fuel resistance, flexibility and temperature range. NBR is widely used in hydraulic systems, pneumatics, machinery, pumps and general industrial applications.
An important advantage is its good resistance to many mineral oils and greases. However, the exact properties vary by compound. For applications involving specific chemicals, high temperatures or special requirements, it is therefore important to check the technical specifications of the relevant version. View our range of NBR O-rings in different sizes and designs.
FKM, also referred to as FPM and in many cases known under the Viton® brand name, is a fluoroelastomer widely used when higher temperature and chemical resistance are required. FKM O-rings are used in the automotive industry, chemical industry, mechanical engineering and various industrial applications. The material offers good resistance to many oils, fuels and other media.
Actual resistance depends on the specific compound, temperature and medium. For critical applications, it must therefore always be verified that the selected version is suitable. FKM is available in different hardnesses and compounds, allowing the correct version to be matched to the application. If you are unsure whether FKM is suitable for your application, we can advise you on the available options.
EPDM is widely used when a seal needs to withstand water, hot water, steam, weathering, ozone and certain glycol-containing fluids. For applications where flexibility across a wide temperature range is important, VMQ/silicone and FVMQ/fluorosilicone can be interesting options. We also supply HNBR, ACM, FFKM, IIR, CR and AU/polyurethane.
FFKM, for example, is used in situations where extremely high demands are placed on chemical resistance and temperature. The correct material always depends on the complete application. Selecting a material based on only one property can therefore lead to problems. Consult the material overview or contact us for advice if you are unsure between different elastomers.
O-rings are used in virtually every technical sector where liquids or gases need to be sealed. In hydraulic systems, for example, they are used in cylinders, valves, connections, pumps and other components. In pneumatic systems, they seal compressed air and other gases. O-rings are also common in industrial machinery, compressors, drive systems and process installations.
A major advantage is that the same basic shape can be manufactured in many different materials, hardnesses and dimensions. This makes it possible to select a suitable seal for a wide range of applications.
The correct choice depends strongly on the operating conditions. An application involving water, for example, requires different properties from one involving hydraulic oil, fuel or aggressive chemicals. Temperature and pressure can also influence the material selection. In dynamic applications, movement and friction must also be considered. For food, drinking water and certain medical applications, specific certifications may also be required.
These may include FDA, NSF, USP, KTW or WRAS, depending on the application and the specific product. Not every O-ring automatically has every certification. Always check the specifications of the selected product.
In hydraulic applications, seals must be resistant to the hydraulic fluid, pressure and temperature involved. NBR is widely used in hydraulic systems because of its properties with many mineral oils and greases. FKM can be an interesting option when higher temperatures or specific chemical conditions are involved. In pneumatic systems, NBR and certain other elastomers are commonly used.
In dynamic applications, friction between the O-ring and the moving component is also important. Incorrect material selection, insufficient lubrication or an incorrect groove can lead to premature wear or leakage. In hydraulic and pneumatic applications, both the seal and the construction in which it is installed must therefore be carefully assessed.
In industry, O-rings are used in pumps, valves, compressors, machine components, couplings and process installations. Requirements can vary significantly between applications. A pump, for example, may involve a combination of pressure, temperature and movement, whereas a flange primarily requires a static seal. The chemical composition of the medium can also be decisive.
For this reason, we consider not only the size of the seal but, where necessary, also the material, hardness, temperature, pressure and medium. For specific industrial applications, we can help select a suitable version and, if necessary, propose an alternative based on the technical specifications.
Selecting the correct O-ring starts with gathering the most important information about the application. First check the required size and then determine which material is suitable for the medium. Next, factors including temperature, pressure and movement must be considered. The groove in which the seal is installed is also important. The correct combination of these factors ensures that the O-ring is sufficiently compressed without unnecessarily stressing the material.
For dynamic applications, factors such as friction, surface speed and lubrication must also be considered. Critical applications may additionally require certifications or specific material approvals.
Hardness, usually expressed in Shore A, is another important property. A common version is 70 Shore A, although other hardnesses are also available. A softer O-ring may seal more easily in certain situations, while a harder compound can offer advantages under certain pressure conditions. The optimum hardness, however, depends on the complete application. The finish of the sealing surfaces and groove geometry also play a role.
It is therefore not advisable to make a selection based solely on hardness. If you provide the application, size, temperature, pressure and medium, we can help determine a suitable version.
When selecting O-rings, we recommend checking at least the following information: inside diameter, cross-section, material, hardness, medium, temperature, pressure and application type. Some applications may additionally require a specific standard, certification, colour, coating or compound. A coating can, for example, be used as an installation aid or to reduce friction. Depending on the application, various coatings are available, including silicone grease, PTFE, Molykote or talc.
Even when a standard O-ring is not immediately available, an alternative material, brand or design may be possible. If in doubt, contact us before ordering a seal. This prevents an O-ring from being selected that fits dimensionally but is technically unsuitable.
Chemical resistance is one of the most important factors when selecting a seal. An O-ring may come into contact with water, oil, grease, fuel, gas, diesel, petrol, alcohol, acids, alkalis or other chemicals. Not every elastomer reacts to these substances in the same way. Temperature can also have a major influence on resistance.
A material that is suitable for a particular medium at room temperature may not provide the same performance at a much higher temperature. Concentration, pressure and exposure time can also play a role. It is therefore important to consider the complete operating conditions when selecting the material.
NBR is often used with mineral oils and certain fuels, while EPDM can be suitable for many applications involving water, hot water and steam. FKM provides good resistance to many oils, fuels and chemicals. FFKM is used in applications with extremely high requirements for chemical resistance and temperature. However, these properties depend on the specific compound.
It is therefore not sufficient to consider only the material name. For a reliable selection, you can use our chemical resistance guide for O-rings to check which materials may be suitable for contact with different substances.
For water-related applications, EPDM compounds are often used, depending on the temperature and type of water. For oil and many mineral oil products, NBR and FKM are commonly used materials. For fuels, higher temperatures or specific chemicals, FKM may be a suitable choice. Specialised compounds such as FFKM are available for highly aggressive media. Nevertheless, every application must be assessed individually.
If you are unsure about chemical resistance, we can help assess the available material options. If an existing seal is experiencing problems, an O-ring failure analysis can also help identify the cause of leakage, swelling, hardening, cracking or other damage.
For many technical applications, not only the size and material are important, but also the standard with which a seal must comply. O-rings are available according to different dimensions and standards, including metric sizes and AS568. Depending on the application, standards and approvals such as ISO, DIN, FDA, NSF, USP, KTW and WRAS may also be relevant. Requirements relating to REACH and RoHS may also apply to industrial products.
Which standard or certification is required depends on the application, the medium used and the requirements of the machine or installation manufacturer. Always check the product specifications before selecting an O-ring for a critical application.
In addition to standard O-rings, we can supply various designs and additional options. These include different hardnesses, compounds, colours and coatings. Certain O-rings can also be supplied with specific approvals or according to particular technical requirements. For demanding applications, it is important that not only the nominal size but the complete product specification corresponds to the requirements of the installation.
When replacing an existing seal, information such as material, hardness, size, manufacturer or product number can help identify a suitable alternative. We supply O-rings from different brands and can, where necessary, propose an alternative if a specific type is unavailable.
Correct O-ring installation is important to maximise service life. Before installation, check the size, material and the seal itself for damage. The groove and sealing surfaces must also be clean and free of sharp edges, dirt and other damage. During installation, the O-ring should not be cut, twisted or unnecessarily stretched. Depending on the application, a suitable installation aid or lubricant can be used.
This product must of course be compatible with the material and the medium used in the application. For dynamic seals, surface quality, friction and movement are also important. Correct installation prevents many problems that might otherwise incorrectly be attributed to the material.
If an O-ring leaks or becomes damaged prematurely, there may be several causes. Incorrect dimensions, incorrect groove dimensions, insufficient compression, excessive compression, extrusion, wear or incorrect material selection can all play a role. High temperatures, chemical attack and unsuitable installation methods can also cause damage. Common forms of damage include cracking, swelling, hardening, flattening and wear.
Our O-ring failure analysis allows you to review various possible causes and solutions. For technically complex problems, we can also assist in analysing the existing seal.
Would you like to order O-rings? You can use our O-ring webshop to search for the required size, material and design. We supply O-rings in various dimensions and elastomers, including NBR, FKM, EPDM, HNBR, VMQ, FVMQ, ACM, FFKM, IIR, CR and AU. In addition to standard metric sizes, inch and AS568 versions are also available. If you do not know the exact size, you can use our O-ring calculation tool or contact us.
We can also assist with questions about chemical resistance, material selection, hardness, certifications or alternative designs.
We supply various industrial sectors and can provide both standard O-rings and specific designs. If a particular type is not immediately available, we can, where possible, find an alternative based on the technical specifications. In addition to O-rings, we also supply other sealing solutions and offer additional services.
These include O-ring testing, where properties such as hardness and tension can be investigated. You can also use our various services and tools for O-rings. This allows you not only to order the correct seal, but also to receive support with selecting, checking and analysing your O-ring.
Do you need a specific size, material or design? View our range of O-rings. Do you need help determining the correct seal? Contact us and, if possible, provide the size, medium, temperature, pressure and application. Based on this information, we can help you find a suitable O-ring.
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