Professional O-Ring and Oil Seal Manufacturer, Sealing Solution Supplier Since 2008.
O-Rings: Types, Materials, and Selection Guide
What is an O-Ring?
An O-ring is a circular sealing element with a round cross-section, typically made from elastomeric materials. It is one of the most common and versatile seals used in both static and dynamic applications. The O-ring is seated in a groove and compressed between two mating surfaces, creating a seal through the deformation of its cross-section. This compression generates contact pressure that prevents the leakage of fluids or gases.
The sealing mechanism relies on the elasticity of the rubber compound. When compressed, the O-ring returns to its original shape, maintaining contact with the groove walls. In dynamic applications, the O-ring also benefits from the lubricating properties of the sealed medium, which helps reduce friction and wear.
Common Types of O-Rings
O-rings are available in a wide range of standard and custom configurations. The most common types include:
| Type | Description | Typical Application |
|---|---|---|
| Standard O-Ring | Circular cross-section, uniform compression | General-purpose sealing in static and dynamic systems |
| AS568 O-Ring | Standardized by SAE AS568 (imperial sizes) | North American industrial and automotive applications |
| Metric O-Ring | Standardized by ISO 3601 (metric sizes) | European and Asian industrial equipment |
| JIS O-Ring | Japanese Industrial Standard sizes | Japanese machinery and automotive |
| X-Ring (Quad-Ring) | Four-lobed cross-section, reduced friction | Dynamic seals requiring lower breakaway force |
| Back-Up Ring | Anti-extrusion device used with O-rings | High-pressure hydraulic systems |
| Encapsulated O-Ring | PTFE/FEP jacket over elastomer core | Chemical-resistant sealing |
Each type is designed for specific operating conditions. The choice depends on factors such as pressure, temperature, media compatibility, and whether the application is static or dynamic.
Material Selection for O-Rings
The performance of an O-ring is heavily influenced by the rubber compound used. Common materials include:
| Material | Temperature Range | Key Properties | Typical Applications |
|---|---|---|---|
| NBR (Nitrile) | -30°C to +100°C | Excellent oil resistance, good wear resistance, low cost | General-purpose seals for motors, pumps, gearboxes |
| FKM (Viton) | -20°C to +200°C | Outstanding heat and chemical resistance | High-temperature engines, chemical processing, aerospace |
| EPDM | -40°C to +150°C | Excellent water and steam resistance | Water pumps, brake systems, outdoor equipment |
| Silicone (VMQ) | -60°C to +200°C | Wide temperature range, good flexibility | Food processing, medical devices, extreme cold |
| FFKM (Perfluoroelastomer) | -20°C to +325°C | Ultimate chemical and heat resistance | Semiconductor, pharmaceutical, aerospace |
| PTFE | -200°C to +260°C | Chemical inertness, low friction | High-speed, chemically aggressive environments |
| PU (Polyurethane) | -30°C to +105°C | High wear and extrusion resistance | Heavy-duty hydraulic cylinders, construction machinery |
The choice of material must consider the operating temperature, the fluid being sealed, and the shaft speed. For example, NBR is suitable for most mineral oils, while FKM is required for synthetic oils and high temperatures.
Key Selection Criteria
When selecting an O-ring, consider the following parameters:
Inner Diameter (ID) – the seal must match the groove dimensions with the correct inner diameter and tolerance.
Cross-Section (CS) – the thickness of the O-ring cord, which determines compression and sealing force.
Operating Temperature – ensure the material can withstand both continuous and peak temperatures.
Pressure – standard O-rings handle low pressure; for higher pressures, use a back-up ring or a harder compound.
Speed – high speeds generate heat; choose low-friction materials like PTFE or FKM.
Medium – compatibility with the lubricant, water, chemicals, or gases being sealed.
Compression Set – the permanent deformation of the elastomer after prolonged compression; lower compression set means longer seal life.
Why Choose Forever Seals?
At Forever Seals, we supply O-rings in a full range of standard and custom sizes. With over 17 years of experience in the sealing industry, we offer:
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Standard sizes from stock for quick delivery
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Custom sizes based on your drawings or samples
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Wide material selection including NBR, FKM, EPDM, Silicone, FFKM, PTFE, and PU
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AS568, JIS, and metric standard compliance
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Factory-direct pricing and fast lead times
Whether you need a simple standard O-ring or a custom sealing solution for a demanding application, our engineering team can help you select the right product.
Get a Quote
If you have any requirements, please send us your specifications (size, material, quantity, application). We will provide a detailed quotation within 24 hours.
