This article takes an in depth look at the use, manufacture, and types of rubber O rings.
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A rubber O ring is a mechanical gasket shaped like a torus or donut, utilized in both static and dynamic applications where parts move in relation to one another, potentially causing friction. Key advantages of rubber O rings include cost-effectiveness, ease of manufacturing, dependability, pressure resilience, and straightforward installation. These rings are crafted from various rubber types such as nitrile, viton, silicone, and other synthetic rubber compounds.
In choosing the appropriate rubber type for O-ring applications, several critical factors are considered: chemical compatibility, hardness, abrasion resistance, permeability, heat resistance, and pressure tolerance. Given the extensive selection of rubber O rings, engineers can select the one that perfectly aligns with the particular needs and operational conditions of their application.
Selecting the best rubber O-ring material is crucial for achieving optimal sealing performance, chemical compatibility, and long service life in a wide range of industrial and commercial applications. Rubber O-rings—also known as elastomeric gaskets or sealing rings—are precision-engineered components used to prevent fluid or gas leakage at joints and connections. Their cost-effectiveness, flexibility, and reliability make them a mainstay solution across numerous sectors, from automotive and aerospace to plumbing, food processing, and electronics manufacturing.
In recent years, the demand for premium rubber O-rings has surged due to expanding uses in water filtration systems, hydraulic and pneumatic valves, industrial pumps, electrical equipment, enclosure seals, rotating motor shafts, lighting fixture pipework, and high-pressure flange gasket assemblies. Their enduring popularity is attributed to their outstanding elasticity and durability, enabling versatile sealing under static and dynamic operating conditions.
Rubber O-rings are classified into two main types: static O-rings, designed for stationary sealing, and dynamic O-rings, built to perform in applications where motion—such as rotary or reciprocating shafts—is present. Understanding the differences in O-ring application ensures proper material selection based on specific operating environments and user requirements.
Nitrile, a synthetic rubber composed of acrylonitrile (ACN) and butadiene, remains an industry-standard sealing material for O-rings due to its balance of performance, affordability, and chemical resistance. Depending on the ACN-to-butadiene ratio, Nitrile O-rings can be customized for varied levels of oil, gas, and solvent resistance, as well as for temperature flexibility. Lower ACN content enhances low-temperature performance, while higher ACN boosts solvent resistance.
The widespread use of nitrile elastomer O-rings is attributed to their economical pricing, low compression set, high abrasion resistance, and superior tensile strength. NBR O-rings are ideal for sealing petroleum-based oils, hydraulic fluids, lubricants, and certain fuels, making them prevalent in automotive, aerospace, hydraulic, and industrial machinery sectors. These O-rings deliver reliable sealing performance within a broad operating temperature range of �40°C to 120°C. Their versatility and value make NBR O-rings a top choice for general-purpose sealing applications.
Viton fluoroelastomer O-rings, derived from FKM synthetic rubber, are engineered for high-performance industrial sealing in extreme and chemically aggressive environments. Developed by DuPont, Viton combines the chemical resistance of fluoropolymers with the flexibility of elastomers. Viton A grade, containing 66% fluorine, is the industry benchmark for O-ring applications demanding superior resistance to harsh chemicals, solvents, and fuels.
Although Viton O-rings may have a higher initial cost than Nitrile, their extended lifespan and unparalleled resistance to heat, ozone, oxidation, and chemical exposure deliver long-term cost savings. Their temperature stability spans �20°C to 210°C, accommodating rigorous sealing in automotive fuel systems, aerospace fluid transfer, and aggressive chemical processing lines. Viton O-rings excel in withstanding oils, acids, silicone fluids, hydraulic fluids, and aromatic hydrocarbons—while maintaining resilience against UV light, fungus, and mold growth. For industries prioritizing chemical compatibility and minimal maintenance, Viton FKM O-rings are the preferred solution for critical sealing tasks.
Silicone rubber O-rings, made from a cross-linked polymer matrix of silicon, oxygen, hydrogen, and carbon, are prized for their biocompatibility, flexibility, and exceptional temperature performance. With added methyl, phenyl, and vinyl groups enhancing their characteristics, silicone O-rings offer outstanding resistance to UV degradation, ozone, weathering, and a wide array of chemicals. These non-toxic, easily sterilized O-rings are frequently selected for food-grade, medical, and pharmaceutical equipment—having achieved FDA and USP Class VI approvals for applications in food processing, beverage production, and sanitary sealing.
Silicone O-rings operate efficiently within a remarkable temperature spectrum of �60°C to 225°C, with specialized formulations rated from �100°C to as high as 300°C. While silicone O-rings provide excellent flexibility and are resistant to corrosion and microbial growth, they exhibit lower tensile strength and reduced wear resistance compared to other elastomers. To enhance durability in demanding environments, a Teflon (PTFE) sleeve may be incorporated. Common industries utilizing silicone O-rings include food and beverage processing, medical device manufacturing, aerospace, and electronics, where cleanroom and contaminant-free environments are critical.
Neoprene (chloroprene rubber or CR) remains a strong choice for O-ring materials where resistance to environmental factors is essential. Created via the emulsion polymerization of chloroprene, neoprene offers a unique blend of moderate oil, chemical, and weather resistance for O-ring seals. Its stable molecular structure provides resilience against UV light, ozone, aging, and oxidation, making it an optimal elastomer for outdoor and marine applications.
Manufactured through sulfur curing, neoprene O-rings demonstrate low flammability—they can self-extinguish once the flame source is removed. This flame-retardant property is valuable for safety-focused sealing in refrigeration, HVAC, and select automotive systems. Neoprene O-rings withstand service temperatures between �40°C and 121°C and are suitable for sealing applications involving refrigerants, ammonia, silicone fluids, coolants, and select petroleum-based lubricants. Their adaptability to diverse operating environments makes them a reliable solution for general industrial and mechanical uses.
Natural latex rubber O-rings are sourced from the processed sap of rubber trees and undergo prevulcanization to yield an elastomer renowned for its exceptional flexibility, stretch, and strength. Latex O-rings offer excellent tensile strength and superior elongation properties, making them well-suited for dynamic sealing tasks that require frequent expansion and contraction.
While latex exhibits robust performance at low temperatures, it is sensitive to heat, sunlight, and oxygen, and is subject to material degradation unless treated with suitable stabilizers. Latex is not recommended for use with petroleum oils, fuels, or most solvents due to rapid deterioration in such chemical environments. Industries that benefit from latex O-ring use include laboratory, sports equipment, and select medical and pharmaceutical sectors—especially for applications where biocompatibility, resilience, and high flexibility are critical.
Polyurethane O-rings, formed by reacting polyols with diisocyanates, are valued for their remarkable wear and abrasion resistance, high tensile strength, and excellent elasticity. As a thermoplastic elastomer, polyurethane enables custom performance tuning for specific sealing conditions. These O-rings endure demanding mechanical stress, frequent movement, and exposure to hydraulic fluids, oils, fuels, and a range of chemicals.
Operating effectively between �54°C and 225°C (depending on compound selection), polyurethane O-rings are favored for applications subject to high pressure, recurring impact, and abrasive conditions—such as hydraulic cylinders, pneumatic actuators, mining equipment, and automotive parts. Their low permeability to gases and resistance to extrusion further expands their practical utility for hydraulic and pneumatic sealing technology.
The six natural and synthetic rubber compounds described above represent only a portion of the full spectrum of O-ring materials available on the market. Other specialty elastomers and engineered polymers are often specified for advanced sealing solutions requiring extreme temperature stability, aggressive chemical resistance, or compliance with regulatory standards (such as FDA, USP, or NSF requirements).
Key alternative O-ring materials include:
When selecting the ideal O-ring material, carefully consider user intent and application-specific requirements: temperature extremes, pressure ratings, regulatory compliance, media compatibility, and dynamic versus static sealing conditions. Consulting with experienced O-ring manufacturers or material engineers ensures proper material selection for maximum sealing effectiveness and product longevity.
| O Ring Materials | |
|---|---|
| Aflas™ | Perfluoro elastomer |
| Fluorocarbon FFKM | Fluorez |
| HNBR | PTFE |
| PEEK | HNBR |
| TPV(EPDM+PP) | Butyl |
| FFKM | Chlorosulfonated Polyethylene |
| EPDM | Epichlorohydrin |
The initial classification for rubber O rings is static and dynamic, where static rubber O rings form a seal for two surfaces that do not move, while dynamic rubber O rings make a seal between surfaces that do move. The different functions require the use of materials to fit their applications.
Static rubber O-rings don’t need to be made from hard-wearing or highly resilient materials. In contrast, dynamic rubber O-rings require careful manufacturing due to their exposure to abrasion, shearing forces, compression, and stress, which can lead to their failure. Additionally, dynamic O-rings often require frequent and substantial lubrication.
The variety and complexity of rubber O-rings are expanding daily as new and innovative designs emerge. Rubber O-rings are distinguished by their diameter, thickness, shape, function, and material.
Back-up O-rings are used to protect primary O-rings from extrusion under high pressure and temperature conditions. They minimize or block the extrusion space, preventing the primary O-ring from being pushed through the gap. By incorporating back-up O-rings, the performance of the primary O-rings is enhanced, allowing them to withstand higher pressures and temperatures.
In the diagram below, the extrusion points are indicated on both the right and left sides, where backup O-rings are installed as barriers.
The primary purpose of coating rubber O-rings is to enhance their resistance to friction, weathering, chemicals, and abrasion. Once coated, rubber O-rings become less sticky and are less likely to twist or tear during assembly. These coatings come in various colors, further improving the durability and performance of the O-rings.
Encapsulated rubber O-rings feature a core of flexible rubber encased in a protective jacket that shields against corrosion and high temperatures. The common types of jackets used are fluorinated ethylene propylene (FEP) and perfluoroalkoxy-copolymer (PFA).
FEP resists a range of destructive chemicals and operates across a broad temperature range. PFA, similar to FEP, offers enhanced mechanical properties and greater resistance to stress and cracking.
The jackets of encapsulated rubber O-rings can be damaged by moving parts, which restricts their use to static applications.
Hollow rubber O-rings share the same shape as traditional O-rings and behave similarly when force is applied, flowing into a groove. The key difference is that hollow rubber O-rings are easier to compress and fill the groove more readily. However, they are not suitable for dynamic or high-pressure applications but can be used in both standard and non-standard grooves.
Square rubber O-rings feature a square cross-section and are sometimes referred to as washer or lathe-cut rings. These highly flexible O-rings are designed to create leak-proof connections. When installed in a groove and compressed, the square rubber O-ring molds to the shape of the groove, ensuring a secure and permanent seal between the two surfaces.
A rubber O-ring is designed to create a tight, secure, and leak-proof seal for various applications, including products, process control systems, and motor shafts. Its popularity as a sealing solution stems from its straightforward design, ease of manufacturing, and simple installation.
Rubber O-rings leverage the primary property of rubber—its elasticity, or compression set. When compressed between two surfaces, the elastic force of the O-ring pushes back to create a seamless seal.
The temperature resistance of a rubber O-ring depends on the type of rubber used in its manufacture. Generally, there are three temperature criteria to consider:
Different types of rubbers vary in their resistance to solvents, esters, ketones, petrochemicals, fluoroalkanes, and acids. Chemical compatibility is crucial for the success of a rubber O-ring and must be carefully considered when selecting one for a specific application. Generally, compatibility can be categorized into three types:
Hardness measures a material's resistance to deformation when force is applied. It can be categorized into three types: scratch hardness, indentation hardness, and rebound hardness.
Durometer is the international standard for measuring the hardness of materials like rubber O-rings. Durometer readings increase in increments of five or ten, such as 50, 60, 65, 70, and 75. Most rubber O-rings typically have a durometer reading of either 70 or 90.
The three common types of durometer gauges are Types A, M, and D. Type A is used for measuring the hardness of soft rubber, while Type D is designed for harder rubber. Type M is used for measuring the hardness of very small, soft rubber O-rings.
Soft materials with a low durometer reading, such as 50 durometer, can easily flow into microfine grooves or fill imperfections and deformities. However, they may experience issues with wear and extrusion.
The harder a material or the higher its durometer reading—such as 70 or 90 durometer—the more resistant the rubber O-ring is to extrusion, making it suitable for use in dynamic applications.
Tensile strength measures the amount of force a material can withstand before fracturing or breaking, and it is the opposite of compression strength. Understanding tensile strength is crucial for applications where materials are subjected to pulling forces, as it helps designers predict how a product will respond to such stresses.
Among the various rubber O-ring materials, silicone has very low tensile strength, which makes it unsuitable for dynamic sealing applications.
Tensile strength is measured using a tensometer, a machine designed to apply either tensional or compressive forces. The results are displayed on a stress-strain curve, which illustrates the amount of force required to deform or break the material.
When purchasing rubber O-rings, other factors should also be considered. Typically, these conditions are already evaluated by designers and engineers, as reliable O-rings are crucial for the success of a process.
The chart below offers an overview and comparison of different rubber materials and their properties.
| Material Properties Comparison Chart | ||||||||
|---|---|---|---|---|---|---|---|---|
| Material | Nitrile | Butyl | Neoprene | Ethylenepropylene | Fluorocarbon | Polyurethane | Silicone | Perfluoroelastomer |
| Property | NBR | IIP | CR | EPDM | FKM | AU or EU | VQM | FFKM |
| Ozone Resistance | P | G/E | G/E | P | E | E | E | E |
| Weather Resistance | F | G/E | E | E | E | E | E | E |
| Heat Resistance | G | G/E | G | E | E | F/G | E | E |
| Chemical Resistance | F/G | E | F/G | E | G | P | F/G | E |
| Oil Resistance | E | P | F/G | P | E | G | F/G | E |
| Impermeability | G | E | G | F | G | F/G | F/P | G |
| Cold Resistance | G | G | F/G | G/E | F | G | E | F |
| Tear Resistance | F | G | G | G/E | F/G | G/E | P | P |
| Abrasion Resistance | G | F/G | G | G/E | G | E | P | E |
| Set Resistance | G/E | F/G | F | G/E | G/E | F | G/E | P |
| Dynamic Resistance | G/E | F/G | F | G/E | G/E | F | G/E | P |
| Acid Resistance | F | G | F/G | G | E | P | F/G | E |
| Tensile Strength | G/E | G | G | G/E | G/E | E | P | P |
| Electrical Properties | F | G | F | G | F | F | G | E |
| Water Steam Resistance | F/G | G | F | G | F | F | G | E |
| Flame Resistance | P | P | G | P | E | P | F | G |
| P = Poor | F = Fair | G = Good | E = Excellent | |||||
Rubber O-rings are among the simplest precision mechanical parts, yet they play a crucial role in ensuring the high performance of products, machinery, and components. Their use is expanding with the development of new and innovative processes and procedures. Despite their simplicity, they are essential to numerous operations and processes.
Rubber O-rings come in an extensive range of sizes, shapes, and configurations, from those small enough to fit in a pen to those large enough to seal pipelines. This versatility makes them suitable for a wide variety of processes and operations. As modern devices become smaller and more adaptable, rubber O-rings are being re-engineered and resized to meet these evolving requirements.
While hardness is crucial for various applications, the durometer of rubber O-rings can be adjusted to achieve the desired texture for each specific use. Rubber O-rings range from extremely soft ones that can be easily squeezed with a finger to those hard enough to withstand hammering, making them adaptable to a wide range of conditions.
All rubber O-rings, whether customized or standard, feature a very simple structure and design. This simplicity ensures that they are easy to install and replace, regardless of the application.
Due to their simplicity, rubber O-rings self-seat without requiring any instruments or tool adjustments, which also means they typically require minimal to no maintenance.
The primary function of a rubber O-ring is to create a tight and secure seal that prevents leakage. This key attribute is why rubber O-rings continue to be widely used.
Among the materials essential for complex operations, rubber O-rings are the least expensive and most readily accessible.
Several factors can contribute to rubber O-ring failure. These include issues related to initial use, such as improper installation or inadequate consideration of compression levels in a process. Understanding these factors can help prevent future problems and safeguard devices and equipment.
Unlike gaskets, rubber O rings have a circular design with rounded edges and are made from a variety of elastomers. They are molded to fit the needs of a specific profile. The design of rubber O rings prevents fluids from escaping and are typically used on hydraulic and other high pressure devices. They are a cost effective tool suited for static and dynamic applications.
Abrasion is a common cause of rubber O ring failure and can result from an improper finish to its surface when used in a dynamic process. Dynamic rubber O rings are required to be lubricated and must be capable of holding a lubricant. In other instances, the system where the rubber O ring is placed may not be providing enough lubricant.
Swelling in a rubber O-ring occurs when it absorbs surrounding fluids. If the O-ring material is incompatible with the temperature, fluid type, or system environment, swelling can continue beyond a critical point. This uncontrolled swelling can result in gland fill, extrusion, and eventual loss of the seal.
In most cases, the chosen elastomer is incompatible with the environment and cannot properly interact with the fluids involved.
In addition to abrasions, compression sets are a common cause of rubber O-ring failure. This issue occurs when the seal line's integrity is compromised due to improper seal squeeze. Typically, rubber O-rings rebound to their original shape after compression. However, if stretched beyond their recommended limit, the cross-section can become reduced and flatten into an oval shape, diminishing the O-ring's ability to form a tight seal.
Compression set failure can result from several factors, including the use of rubber O-rings with poor compression set properties. Other contributing factors are improper gland design, excessive temperature, swelling, over-tightening, and exposure to incompatible fluids.
The success and longevity of rubber O-rings heavily depend on proper and timely lubrication. Issues such as abrasion, scratches, pinching, and deformations often arise from inadequate lubrication. Although rubber O-rings can be coated or encapsulated, they still require additional protection through lubrication. Without it, O-rings can experience degradation and damage, potentially leading to significant failures in processes and devices.
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