‘O’ RINGS
‘O’ Rings, also known as a toric joint, are a mechanical gasket in the shape of a torus, a loop of elastomer with a disc shaped cross section, designed to be seated in a groove. These ‘O’ rings are an exceptionally versatile sealing device and may be used in static or dynamic applications and are produced from a wide selection of elastomeric materials.
‘O’ Rings are one of the most common seals used in machine design as they are relatively inexpensive to manufacture, reliable and have simple mounting requirements., being capable of sealing tens of megapascals of pressure. ‘O’ Ring selection is based upon chemical compatibility, application temperature, sealing pressure, lubrication requirements, quality, quantity and cost.
SSP stock an extensive range of material compounds and sizes and are also able to offer product with full certification traceability, batch and cure date coding, with individual bagging and labelling meeting both aerospace and critical application requirements.
SSP are certified to ISO 9001:2015 Incorporating AS9120 Aerospace Standard
In addition to the many different material types and BS and Metric size ‘O’ Rings available, we also supply FEP Encapsulated ‘O’ Rings, Completion Plug ‘O’ Rings and ‘O’ Ring Kits and Cord.
Typical General and High Performance materials readily available include;
Aflas – Available in hardness range of 70, 80 and 90 IRHD these compounds are suitable for sour gas duties or where amines and high temperature water or steam are used. They have resistance to lubricants and some fuels and a typical temperature range of -10⁰C to +200⁰C. The main requirement includes oil field and chemical industry applications.
Butyl – Very low gas permeability makes butyl popular for vacuum and high pressure gas applications. It must not be used with mineral oils
Chloroprene (Neoprene) – This general purpose elastomer is largely unaffected by sunlight and atmospheric ageing. It gives satisfactory service in many media such as lubricating oils and greases , dilute acids and alkalis and refrigerants including ammonia, carbon dioxide and freons. Temperature range is typically from -40⁰C to +100⁰C
EPDM – Has excellent resistance to weathering, ozone, hot and cold water and steam. Also have resistance to aliphatic phosphate-ester hydraulic fluids, acids, alkalis, salt solutions, alcohols, glycols and silicone oils. Peroxide cured EPDM materials have better resistance to temperature and chemicals and obtain better compression set values than sulphur cured. Some specific grades do have WRAS approval for use in potable water applications. Not to be used with mineral oil products.
FKM (Viton®) – General Fluoroelastomer grades operate efficiently under severe chemical conditions and at high temperatures where many other seal materials cannot survive. Dependent upon choice of grade they can be well suited to arduous applications involving;
- Temperature Capabilities ranging from –61⁰C to +260⁰C
- Petroleum fuels and Mineral-based hydraulic fluids
- Aliphatic, aromatic and chlorinated hydrocarbons
- Silicone oils and greases
- Vegetable and animal oils and fats
- Non-polar solvents
- Ozone, weathering and aging
FKM is not resistant to;
- Glycol based brake fluids
- Polar solvents
- Superheated steam
- Amines, alkalis and low molecular organic acids
We also stock high performance grades of FKM for specific duties, including;
- FR68/90 – This low compression set elastomer offers excellent resistance to rapid gas decompression (RGD), plus excellent resistance to sour gas, amines and steam/hot water
- FR58/90 – This terpolymer based grade resists RGD and has good all round elastomeric properties
- FR25/90 – Has excellent resistance to sour gas together with improved low temperature characteristics. It is compounded for RGD resistant duties down to -41⁰C
- FR64/70 & 80 – Dipolymer based grades that offer enhanced performance in steam, hot water and mineral acids
Fluorosilicone – Grades are available for applications involving hydrocarbon oils, petroleum fuels and mineral based hydraulic fluids. Primarily used for static seals in aerospace fuel systems. Use may be limited by high gas permeability, low tensile strength and poor resistance to abrasion and tear. Fluorosilicones have substantially better resistance to mineral oils and fuels than normal silicones and have a typical temperature range between -60⁰C and +200⁰C
HNBR (Hydrogenated acrylonitrile-butadiene rubber) – is obtained by selective hydrogenation of the double bond of the butadiene molecules of the NBR rubber. With higher levels of saturation HNBR exhibits distinctly better resistance to high temperatures along with enhanced physical strength and chemical resistance properties
Typical grades and hardnesses of HNBR ‘O’ rings have good resistance to mineral oil-based oils and greases, vegetable oils and fats and aliphatic hydrocarbons and have a typical Temperature range of -30⁰C to +150⁰C.
We also stock two high performance compound grades of HNBR ‘O’ rings, these being;
- Elast-O-Lion 101 and 985 – These materials have excellent oil/fuel resistance of traditional NBR elastomers with a similar ACN content. They also have superior mechanical properties and can sustain higher service temperatures i.e 180⁰C in oil. In addition they also display superior resistance to aggressive fluids such as sour crude oil, lubricating oil additives and amine corrosion inhibitors. These two grades are extremely well proven in oilfield applications where mechanical strength, plus resistance to rapid gas decompression (RGD) (ED-Explosive decompression) and chemical attack is required. Typical temperature range can be -55⁰C to +180⁰C
Polyurethane – Most of the polyurethanes used for the production of seals fall into the category of thermoplastic elastomers due to stress relaxation at +50⁰C. However, they are used as ‘O’ Rings in drive transmissions where tensile strength, elongation characteristics and wear resistance properties prove invaluable for applications with high dynamic loads. However, polyurethanes have low resistance to acids, alkalis and amines, glycol based brake fluid and hot water/steam.
Nitrile (NBR) – is the most widely used material in production and manufacture of ‘O’ Ring Seals. NBR is a copolymer of butadiene and acrylonitrile, having very good mechanical properties, high abrasion resistance, low gas permeability and a high resistance to mineral based oils and greases. There are three main groups of Nitrile and all are differentiated by the Acrylonitrile (ACN) content which can vary generally between 18% and 50%.
- Medium Nitrile grades usually have an ACN content of roughly 30% and are the most commonly used of all polymers in hydraulic sealing.
- High Nitrile will have an ACN content nearer to 50% and will be used in applications coming into contact with aromatic fuels and mineral oils
- Low Nitrile will have an ACN content nearer to 18% and are primarily used for low temperature applications.
Silicone – these elastomers have excellent resistance to weathering, ageing, ozone, oxygen and ultraviolet radiation and offer good resistance to compression set at high temperatures along with excellent electrical resistance. Silicone is very good in food and medical applications. Silicone is limited for use due to its low tensile strength and poor resistance to tear and abrasion. Typical temperature range is -60⁰C to +200⁰C (230⁰C with special grades)
FFKM – These materials have excellent heat resistance, capable of being exposed to temperatures above 300⁰C. The resistance to chemicals is nearly universal and compares to that of PTFE. The great value of this group of products is having the chemical and thermal stability of PTFE combined with the elastic properties of an elastomeric compound.
These specially designed and developed group of base compounds are specifically used where safety requirements and high maintenance input can be used to offset and justify the very high unit cost of production. Dependant on material grade selected the temperature range of this group of products is between -40⁰C to +340⁰C
- Kalrez® (DuPont™) – This is a particularly recognised compound group containing a range of different grades of FFKM perfluoroelastomer compounds that offer almost universal chemical resistance, with grades available for continuous duties up to 325⁰C.
Frequently Asked Questions
What is an o ring?
A simple component that provides an essential function, an o ring (or packing joint) is a round or doughnut-shaped elastomer that sits in the groove of two mating surfaces, creating a tight seal to prevent leaks.
O rings come in various materials, all with multiple benefits and suitability requirements, considering strengths, weaknesses, and tolerance levels. Therefore, finding the right o ring material suitable for your application and use is vital.
A must-have in mechanical engineering, o rings support the development of new applications and products and, ultimately, help keep work environments safe.
What is the purpose of an O-ring?
The main purpose of an o ring is to prevent liquids and gases from escaping from an application or product by connecting two or more parts interlocked by the o ring.
O rings are placed in the groove between two surfaces, so when these two surfaces are compressed together, there is no longer a visible gap or clearance. The o ring provides a tight seal.
There are two main types of o rings, static and dynamic.
Static o rings – suitable for two surfaces that do not move.
Dynamic o rings – provide a suitable seal between moving parts.
What is the difference between gasket and O-ring?
Gaskets are flat material components used between two flat surfaces (with a bolted joint), compared to o rings that are round in shape and sit in a groove between two surfaces.
You can customise an o ring’s size and density to suit specific requirements, whereas we layer gaskets with different coatings depending on the application.
O rings will perform better than gaskets in applications that require extreme pressure, with o rings returning to their original shape.
Both o rings and gaskets can withstand a wide range of fluctuating temperatures; however, gaskets are more suitable to withstand extreme temperatures.
How to shrink an o ring
O rings can expand or swell slightly if they absorb fuel or oil. Hence, shrinking the o ring allows you to pull the fuel or oil out, providing a better fit and a tighter seal.
A quick way to achieve this is by heating the o ring in boiling, clean water for a few minutes, causing the absorbed fuel to vaporise and the o ring to shrink and fit correctly back into place. The o ring will also be clean, removing any other impurities.
You can also leave the o ring in direct sunlight as an alternative option, using the same evaporation principle. However, this method does take longer and won’t clean the o ring.
Where to buy o ring
You will find o rings in most mechanical parts and processes, such as pumps, oil seals, engines, cylinders, boilers, fuel systems, connectors, pipe joints, compressors, valves, etc.
You can buy most standard o rings from hardware stores and local stockists.
Specialist Sealing Products is a reputable, premium supplier of o rings and gaskets. Supplying o rings in various materials and sizes to meet all application requirements and specifications.
We have many years of experience in providing a range of sealing solutions. Trusted and committed to delivering high standards of service and exceptional quality products.
