O-Rings: Universal Sealing Solution for Industry

O-Rings: Proper Selection, Installation, and Maintenance

10 min.

O-rings are a key component in many industries, such as the automotive, aerospace, space, chemical, pharmaceutical, construction, food, beverage, electronic, semiconductor, energy, water management, and irrigation industries. Thanks to their versatile sealing properties, simplicity, and low cost, they have a wide range of uses in many industrial applications.

O-rings: A Universal Sealing Solution for Industry

In all industries, O-rings must meet specific requirements and purposes, such as resistance to temperatures, pressures, chemicals, wear, and degradation. To achieve optimal performance, reliability, and seal life, it is important to choose the right material, dimensions, and O-ring design for the specific application. In this article, we will look at their selection, installation, maintenance, and other topics associated with these essential sealing components.

What are the greatest advantages of using O-rings?

Seal across a wide range of pressures, temperatures, and tolerances.
Easy maintenance, do not require retightening, etc.
Small space requirement.
Low weight.
Can be reused, unlike non-elastic seals.
Service life corresponding, with proper design, to the usual aging period of rubber.
O-ring failure usually occurs gradually, warning of the need for replacement.
Constant compression of the O-ring in axial sealing, preventing its degradation unlike a flat gasket.
The most cost-effective design solution.

Material properties, their advantages and disadvantages

O-rings can be made of various materials that have their specific properties, advantages, and disadvantages. In the following overview, we will focus in more detail on some of the most common materials used for manufacturing O-rings and their characteristics.

NBR (nitrile rubber): this is the most commonly used material for O-rings, which, thanks to its excellent mechanical properties, resistance to oils and greases, excellently resists normal wear and tear. The disadvantage of NBR can be limited resistance to ozone, UV radiation, and certain chemicals. It is suitable for use in the temperature range from -30°C to +100°C.
FKM (fluoroelastomer): material also known under the trade name Viton. FKM is a highly resistant material with excellent resistance to temperatures, oils, fuels, and many chemicals. Its use is possible in the temperature range from -20°C to +200°C. FKM is not recommended for applications with low temperatures, steam, or polar solvents.
EPDM (ethylene-propylene-diene monomer): EPDM is an elastomer with excellent resistance to ozone, UV radiation, aging, and high temperatures. It is suitable for applications with water, steam, and many chemicals, but does not have good resistance to oils and greases. The temperature range of EPDM is from -45°C to +150°C.
MVQ (silicone): Silicone O-rings have excellent resistance to temperatures, aging, ozone, and UV radiation. They are suitable for food and pharmaceutical applications, but have limited resistance to oils, greases, and wear. The temperature range for using silicone O-rings is from -60°C to +200°C.
PTFE (polytetrafluoroethylene): PTFE, known under the trade name Teflon, is a material with exceptional chemical resistance, low friction, and a wide temperature range from -200°C to +260°C.

How to choose the right size and standard of an O-ring

When selecting O-rings, it is important to take into account sizes and standards, which are governed by metric or imperial dimensions. There are also specific standards, such as AS568 (USA) or ISO 3601 (international), which define specific dimensions and tolerances for O-rings.

The following paragraph describes in more detail some of the common standards and factors to consider when choosing the correct O-ring size.

Metric vs. imperial dimensions: O-rings are available in both metric (millimeters) and imperial (inches) dimensions. Metric dimensions are commonly used in Europe and most of the world, while imperial dimensions are more common in the US and the UK. When selecting O-rings, it is important to ensure compatibility with the units used in the specific application.
AS568 (USA): AS568 is an American standard for O-rings, which defines three size series (2XX, 3XX, and 4XX) with different diameters and thicknesses. These standards include more than 350 different sizes and are widely used in the industry.
ISO 3601 (international): ISO 3601 is an international standard that specifies dimensions, tolerances, and designation of O-rings. This standard includes metric dimensions and is widely accepted worldwide. ISO 3601 is divided into several parts dealing with different aspects of O-rings, such as dimensions, classification, and quality control.
DIN 3771 (German standard): DIN 3771 is a German standard for O-rings, which is often used in Europe. This standard defines four tolerance classes and includes more than 200 different sizes.
JIS B2401 (Japanese standard): JIS B2401 is a Japanese standard for O-rings that includes more than 100 different sizes and specifies tolerances and surface finishes. JIS B2401 is widely used in Asian countries.

Which dimensions to consider when choosing an O-ring

Which dimensions to consider when selecting

When selecting the right O-ring, it is important to consider not only standards, but also factors such as outer and inner diameters, ring thickness, tolerances, and surface finishes. The correct selection of the O-ring size will ensure optimal sealing and functionality in the specific application.

The size of an O-ring is given as the inner diameter times the cross-section diameter (thickness) of the ring - d1 x d2. The designation then looks, for example, like this: O-ring 13.6 x 2.3 NBR 90, or 15 x 2 NBR 70.

Outer diameter: The outer diameter of the O-ring is important for the correct positioning of the ring in the groove and ensuring the necessary seal. When selecting the outer diameter, the groove tolerance and the thermal expansion of the O-ring material must be taken into account.
Inner diameter: The inner diameter of the O-ring is crucial for achieving the necessary compression and tightness on the mating surfaces. When selecting the inner diameter, the tolerance of the mating surfaces and the thermal expansion of the O-ring material must be considered.
Ring thickness: The thickness of the O-ring affects its compression and sealing performance, as well as its resistance to extrusion. When selecting the ring thickness, the pressure in the application, the groove size, and the material properties of the O-ring must be taken into account.
Tolerances and surface finishes: Tolerances and surface finishes of O-rings are important for achieving optimal sealing and service life in the application. Higher tolerances and better surface finishes can increase the price of the O-ring, but at the same time improve its performance and reliability.

The correct selection of size and compliance with relevant standards ensures optimal tightness and long service life of O-rings, which is key to successful application in industrial sectors. When selecting an O-ring, it is therefore important to carefully consider all relevant factors and standards.

What not to forget when choosing sealing rings

Choosing the right O-ring for a specific application is essential to achieve optimal performance and seal life. When selecting an O-ring, several factors must be considered, such as operating conditions, pressure, temperature, chemical composition of the medium, and dynamic load.

Operating conditions, such as pressure and temperature, have a significant impact on the choice of O-ring material and dimensions. The O-ring material must be able to withstand the pressure that will act in the application and at the same time must be resistant to temperature changes that may occur during operation. Some materials, such as FKM or EPDM, are resistant to a wide range of temperatures and may be suitable for applications with extreme temperatures.
The chemical composition of the medium with which the O-ring will come into contact is also an important factor when selecting the material. Some materials, such as NBR, are resistant to petroleum products, while other materials, such as FFKM, have high chemical resistance to a wide range of chemicals. It is important to choose a material that is compatible with the chemical components of the media used to prevent degradation of the O-ring and subsequent failure of the sealing function.
The dynamic load to which the O-ring will be exposed is another factor to consider when selecting the right O-ring. Applications with high dynamic loads can cause faster wear of O-rings and require materials with higher wear and friction resistance. In such cases, it may be appropriate to use O-rings with low-friction surface treatments or materials that naturally have low friction, such as PTFE.
Last but not least, the dimensions of the O-ring must be considered, which are critical for achieving a proper seal. It is important to choose the right diameter and thickness of the O-ring so that it is compatible with the groove and ensures sealing without excessive compression or play. When selecting O-ring dimensions, tolerance limits and possible fluctuations in pressure and temperature to which the seal will be exposed must be taken into account. The correct O-ring size will ensure optimal compression of the material while allowing its movement under dynamic loads without losing tightness.

It is always recommended to consult the correct selection of an O-ring with an expert or technical specialist who can provide valuable advice and support in choosing the right material, dimensions, and other specifications for your specific application. This will ensure that the O-ring meets the performance and life requirements in the given application, which will increase the reliability of the entire system and reduce the risk of potential problems and failures.

Choosing the right O-ring for your application is a key step to ensuring a successful and long-lasting seal. When selecting, various factors such as operating conditions, pressure, temperature, chemical composition of the medium, and dynamic load must be considered, and, if necessary, an expert should be consulted to achieve the best results.

Buy only from proven manufacturers

When choosing a supplier of sealing elements, it is important to ensure that the company has experience, reputation, and quality products that meet strict standards and specifications. Some of the most well-known and reliable suppliers on the market include companies like Trelleborg Sealing Solutions, Freudenberg Sealing Technologies, SKF and Dichtomatik.

Furthermore, it is important to conduct thorough research and evaluate their product portfolio, experience in the industry, the quality of materials, and the services they offer. Working with proven suppliers will ensure the best possible quality and performance of seals for your specific applications.