Jun. 09, 2025
Agriculture
O-rings are circular sealing devices with a round cross-sectional profile, usually made from rubber compounds (or elastomers). They are simple, easily replaceable, and can be highly economical, which has helped them remain in use for hundreds of years and spread to every industry. When buying o-rings, the 3 most basic characteristics needed are material, hardness, and size. When all of these are defined by a customer, quoting and ordering are as simple as they can be. When any or all of these are not specified, Sealing Devices can make recommendations based on a handful of end-use details, captured by the acronym STAAMPS:
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As o-rings grew in popularity after their invention, the need to standardize sizing became apparent, leading to the creation of several international standards. The most common standard used in the United States is SAE AS568, which defines over 400 sizes across a range of 5 cross sections. In order to meet demand in an ever-growing number of applications, manufacturers keep molds of many of these sizes readily available to produce thousands of o-rings each day. While the SAE AS568 is the most common, Sealing Devices can supply O-Rings to most international standard sizes. Custom size molded O-Rings can be offered with a one-time tooling charge as well.
Another option, for applications that require non-standard sizes, custom molds may be cut to provide continuous rings in medium and high purchase volumes. Non-standard o-rings can also be fabricated by extruding rubber into a cord and splicing the ends together to meet the required diameter; this option is better for low volumes and can save on tooling costs, especially when the rings can be several feet in diameter. Both cross section and diameter have direct effects on an o-ring’s performance in the conditions below.
A good seal should both conform to the surfaces which it is sealing against and rebound after being squeezed, and rubber’s elasticity and relative softness have contributed to its status as a leading sealing material. However, when rubber is heated above or cooled below its recommended temperature range it starts to lose its ability to rebound; we call this taking compression set. Most common elastomers are only useful between -40°F and 250°F. However, some silicone compounds are resilient below -100°F, and some FFKM compounds can be used at over 600°F. For even more extreme temperatures, there are metal o-rings that seal up to °F.
Many factors of the physical system around the o-ring will affect its ability to seal. The o-ring cross section must be chosen carefully to fit the seal groove: too small of a cross section will not compress enough and allow leaks, while one that’s too large will overfill the groove and start to crack. The diameter of the o-ring depends on the size and style of seal groove: too loose of a diameter will form kinks that can leak, and too tight of a fit can cause the rubber to tear, especially in piston seals and racetrack grooves. The hardness (usually measured as Shore A durometer) will depend on the flange material and finish, as well as the available compressive load; softer materials are preferred for applications with fragile flanges, low fastener load, and somewhat irregular sealing surfaces, while harder materials are better in high-pressure and dynamic applications. When sealing a vacuum, there are even more properties to consider such as permeability and weight loss. O-ring elastomers can also be specially formulated to meet industry-specific standards for aerospace, military, pharmaceutical, food/water, and other use cases, as well as customer-defined requirements such as flame resistance, internal lubrication, and even color.
The recent global supply chain complications have revealed just how important and interdependent all stages in the production process are, even for seemingly simple rubber products. While logistical systems are approaching normalcy again, there are still a number of factors affecting raw material availability. Throughout the last couple years, alternative material recommendations have become a common practice to help customers find more readily available solutions without compromising on necessary performance. In certain cases where specific elastomer compounds are not readily available in standard molded ring sizes, o-ring cord can be spliced to fabricate a fitting substitute.
When elastomers are placed in contact with chemicals that they are incompatible with, they will swell, degrade, and eventually fail, which can lead to costly and potentially dangerous leaks. Different compounds are resistant to different chemicals, so confirming media compatibility is vital in every sealing application, even with often-overlooked media like steam, ozone, and UV radiation. When necessary, PTFE or metal o-rings can provide more comprehensive chemical compatibility. Parker’s O-Ring and Engineered Seals division has compiled an extensive compatibility table for common elastomers.
Under normal conditions, rubber o-rings can typically hold up to 1,500 PSI of pressure, but the actual value will depend on cross section, hardware dimensions, and other factors. When the system pressure becomes excessive, the o-ring will start to squeeze through the clearance gap on the unpressurized side of the sealing groove. This action is called extrusion, and if the pressure is not properly regulated the o-ring can start to break apart from this excessive stress. When high pressures are necessary, extrusion risk can be lowered by decreasing the clearance gap, adding an extra anti-extrusion device, or using a harder seal material (including metal in extreme cases that can exceed 50,000 PSI). Back-up rings are common anti-extrusion devices; these are flat rings made of hard rubber or plastic that minimize the clearance gap available for the o-ring to extrude through. On the opposite end of the pressure spectrum, o-ring compounds can also be formulated to seal against a vacuum or rapid decompression (instantaneous loss of pressure).
O-rings can be used to create both static and dynamic seals. In dynamic applications, we tend to use harder o-rings to prevent excessive friction and seal wear. Some elastomers (rubber compounds) perform better than others in sliding and rotating seals, and there are even special formulations of the same elastomers available to further tailor the results. The type of dynamic motion is important too: sliding is more suited to larger cross sections which better resist twisting in the seal groove, but create more friction than smaller cross sections, which is why greater rotational speeds can be achieved with thinner o-rings. Static systems are usually easier to seal, but the details above remain crucial to choosing an o-ring.
As sealing applications become more demanding in all of the areas outlined above, o-ring suppliers have been pushed to continuously innovate seal materials and designs. Given our ties to manufacturers at the leading edge of these innovations, Sealing Devices is positioned as an expert resource to convert all the intricate end-use requirements into a simple sealing solution. Contact us or fill out a technical request form for help with your next sealed design.
Whether sold individually, in large wholesale batches or - as is increasingly common - as part of a highly flexible range of o-ring kits, the basic form and role of o-rings are generally the same across the board.
Their name, as implied, simply refers to a classic doughnut or torus shape, and they exist purely to create a better, more leak-proof seal between two other components, with the aim usually being to prevent the unwanted escape of gases or liquids. In this sense, they’re effectively a type of gasket - the main difference being that o-rings are more commonly used in very high-pressure environments, where a normal cork, paper or rubber gasket would likely be prone to failure.
In very basic terms, o-ring seals work by sitting in a groove or channel between two surfaces/components that are going to be mated or pushed together. The o-ring, generally made of some form of elastomer, sits in the join between these two parts, and becomes compressed in order to help form a tight seal.
The more internal pressure is applied to this join, the more the o-ring is distorted inside its groove, which can improve its overall sealing force up to a point - but beyond a certain pressure, or under more dynamic workloads, this can cause failure of the seal. It’s important to get the balance right between o-ring material, size and working environment in order to fulfil the role you need it to perform.
O-rings are very commonly found in pumps, cylinders, connectors and valves, helping to seal joins between separate parts and prevent leaking of fluids and gases. They’re used with static, dynamic, hydraulic and pneumatic components, making them an especially versatile solution to a very widespread engineering issue.
As noted above, you’d use an o-ring very similarly to the way you’d use any other type of gasket: the elastomer-based circular cross-section sits in a specially engineered groove (the geometry of which is fairly universal), where it becomes compressed between two or more parts once they’re assembled and interlocked. The resulting o-ring seal is both economical and reliable, as well as relatively resilient and easy to maintain/replace when needed.
One of the key strengths of an O-ring-type seal is that after the parts it joins are disconnected and the compression forces acting on it are removed, it will return to its original shape. Over time, repeating this process will start to have an effect on the resilience and uniformity of the materials and the torus shape of the seal, and ultimately the o-ring will need swapping out for a new one if the seal is to remain tight.
Under pressure, the o-ring will shift in its groove towards the lower-pressure side of the seal, forcing it more and more tightly against the inner and outer walls of the gland created between two components. Up to a point, this will create a tighter and tighter seal, but it’s vital not to put more stress on an o-ring than it’s designed to handle, as too much deformation will eventually cause the seal to start leaking again.
Static and dynamic O-ring seal design differs in a few key ways. A static O-ring is any o-ring designed to contact with two or more surfaces that do not move relative to one another, whereas a dynamic O-ring is one that helps form a seal between moving parts.
On the whole, static o-rings are created from less robust and hard-wearing materials than their dynamic equivalents. It’s also important that the components being joined together in a dynamic environment are carefully designed and finished, such that they will not abrade, shear and eventually destroy the O-ring positioned between them. This is less of a concern for o-rings used in static applications, as the only stress force they’ll be under is usually compression (to which they tend to be fairly resilient).
While all o-rings require some degree of lubrication in order to perform to optimal levels, dynamic o-rings require heavier and more frequent lubrication (as well as more regular checking, maintenance and replacement) than static versions. Different types of dynamic movements - for example, rotary, reciprocating and oscillating - demand that o-rings be manufactured with different material qualities to perform to the optimal level.
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In this section, we’ll look a little more closely at what o-rings do, and some of the applications that they’re very often used for.
High-temperature sealing o-rings are, as the name implies, designed to withstand extreme heat while continuing to provide a reliable seal between two surfaces or components.
This makes them ideal for demanding industries and environments such as oil and gas refineries, chemical processing, or any other scenario where a high-temperature seal is required, such as performance transport applications like turbo engines and aerospace engineering.
There are a number of popular high-temperature o-ring material choices, including nitrile, hydrogenated nitrile, silicone rubber, polyacrylate and more. Securing the best choice in any given scenario will generally be a balancing act between the specific operating temperature needed, and the most economical material option at that performance point.
For more detail on all types of O-ring materials and designated temperature ranges, feel free to contact our expert support team any time - they’ll be glad to offer further advice and assistance on specific high-temperature seals, materials and applications.
Again, all industrial o-ring purchases should be carefully planned with direct reference to the specific role and environment the seal is required to perform in. However, as a rough guide to o-ring temperature rating and use limits, some of the more popular materials on sale generally operate within the following sorts of temperature ranges:
High-pressure resistance is a common requirement of industrial o-rings, along with reliable performance in high temperature and dynamic environments. For a high-pressure seal to work to optimal levels, o-ring design and manufacture again depends on choosing specific materials for better performance under specific conditions.
O-rings function on the principle that even pressure placed on the (more or less incompressible) o-ring material creates predictable deformation patterns around the perimeter of the gasket in its groove. This means there’s a fairly uniform mechanical stress placed on all contacting surfaces of an o-ring.
Provided the internal pressure from fluids being contained stays below a given O-ring's contact stress rating, it’s largely impossible for leaks to occur, even under high pressure. However, mechanical failure under high pressure can easily cause extrusion or destruction of the o-ring, which is why it’s important to choose the right material for the precise environment you’re looking to use it in.
An engine o-ring, especially one used in high performance or turbo engines, is a good example of a product that has to be rugged enough in design and material construction to handle various challenging requirements of temperature, pressure and chemical compatibility.
Many basic rubbers and polymers aren’t suitable for use with oils, fuels or solvent-based compounds. For use in an engine, an oil o-ring has to be created specifically from compatible hybrid materials that allow it to maintain crucial o-ring properties (flexibility, incompressibility) while offering more robust resistance to heat, pressure, o-ring leaking and chemical attack than a standard elastomer typically could.
For more advice and information on suitable products to use as engine o-rings, feel free to contact our customer service team through the support pages on our site.
Plumbing o-ring choices are widespread, given the range of materials, sizes and gauges available for use in ducting and pipework applications, as well as to form tight waterproof seals around taps and other fittings. Choosing the best product for the job depends on finding the correct size and shape for the specific role you have in mind.
Food-grade o-rings have been manufactured to more exacting standards of material composition, such that they’ve been officially declared ‘food safe’ for use in the production and preparation of meals, beverages and dining products.
An approved food-grade o-ring must only consist of the material(s) declared and approved as food safety compliant in the country of manufacture/sale. In the UK, this applies to natural and synthetic rubbers, elastomers and polymers.
To achieve food grade approval, an o-ring manufacturer must also take into account extractable ingredients/compounds if the seal is to be used in direct contact with aqueous, acidic or fatty foods and drinks. Some common food-safe o-ring materials include EPDM, fluorocarbon, nitrile, neoprene and silicone.
Carbon dioxide often presents an issue for many types of o-rings, as softer materials have a tendency to absorb the gas over time and swell up. This can lead to an unreliable seal in the short term, and over time the CO2 will actually cause the o-ring to start to break down from within.
Some popular choices for use in applications where the o-ring will have extended CO2 contact include polyurethane, PTFE, nitrile, and fluoroelastomers. However, the best choice will always depend on the consideration of other environmental or application factors.
Aircraft o-rings and aerospace o-rings generally need to be highly chemically resistant, and able to operate within a wide range of temperatures and pressures in order to keep an aerospace craft’s powertrain running cleanly, efficiently and smoothly. Typical applications include fuel cap gaskets, fuel system o-rings, and valve cover seals.
Common elastomers for use in aerospace-type applications include nitriles, ethylene-propylene, fluorosilicones and more. Because there are so many different sizes and gauges of o-ring distributed throughout most aircraft engines and systems, most sales for aerospace and aeronautics are through bulk orders of multi-size o-ring kits.
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