Understanding the role of O-rings in sealing technology

O-rings are one of the most widely used sealing components across engineering, manufacturing, and maintenance sectors. Known for their simplicity and reliability, they play a vital role in preventing leaks and maintaining pressure integrity in systems handling liquids or gases.

At Ashton Seals, we supply O-rings engineered for precision and durability, ensuring consistent performance across both static and dynamic applications. Whether used in hydraulic systems, pneumatic assemblies, or mechanical devices, our sealing products provide a dependable barrier against fluid and gas leakage.

What is an O-ring?

An O-ring is a circular elastomeric seal designed to sit within a groove, known as a gland, and is compressed between two surfaces to form a tight, leak-proof barrier. This compression allows the O-ring to deform slightly, filling microscopic gaps to prevent fluid passage.
Key features:

• Simple, cost-effective design suitable for a wide range of uses.
• Reliable sealing under both static and dynamic conditions.
• Self-energising action – pressure strengthens the seal.
• Available in various materials to suit diverse temperatures, fluids, and pressures.

The versatility of O-rings makes them indispensable across countless industries, from aerospace and automotive to food processing and general engineering.

How O-rings work

When installed, an O-ring is compressed between two mating surfaces. This compression creates a sealing line that blocks the passage of fluids or gases. As internal pressure increases, the O-ring is forced against the low-pressure side of the gland, improving the seal further. Once pressure is released, the O-ring’s elasticity allows it to return to its original shape, ready for the next cycle.
Performance principles:

• Compression: The O-ring fills the gland and deforms to create a seal.
• Seal formation: The deformation closes the gap between surfaces, preventing leakage.
• Pressure intensification: System pressure enhances contact force, strengthening the seal.
• Elastic recovery: The O-ring returns to its original shape once pressure is removed.

This combination of elasticity and pressure responsiveness ensures reliable sealing performance in a wide variety of operating environments.

How are O-rings measured?

O-rings are measured using two key dimensions: inside diameter (ID) and cross-section (CS). These measurements determine the size, fit, and performance of the seal.
1. Inside Diameter (ID): The distance across the inner circle of the O-ring. This defines the overall size and the component it fits around.
2. Cross-Section (CS): The thickness of the O-ring material, measured from the inner to outer wall. This affects sealing pressure and compression.

Standard O-ring sizes are usually specified according to BS (British Standard) or AS (Aerospace Standard) sizing charts. Ashton Seals provides O-rings in both metric and imperial sizes to ensure compatibility with international equipment and design standards.
To measure an existing O-ring accurately:

• Place it on a flat surface.
• Use a vernier calliper to measure the inner diameter.
• Measure the thickness of the ring to determine the cross-section.
• Understanding these measurements ensures correct selection, reliable sealing performance, and longer service life.

Common applications of O-rings

O-rings are used in almost every sector of engineering and manufacturing. Their simplicity and efficiency make them the go-to choice for sealing applications in:

• Hydraulic systems – maintaining pressure and preventing leaks in pumps and valves.
• Pneumatic equipment – providing low-friction sealing in dynamic operations.
• Automotive components – used in fuel systems, engines, and braking mechanisms.
• Industrial machinery – ensuring leak-free operation in rotary and reciprocating equipment.
• Food and pharmaceutical processing – available in approved materials for hygienic environments.

For more complex dynamic or high-friction applications, consider our X-rings, which offer enhanced stability and reduced wear.

Material choices and compatibility

Selecting the correct material is crucial for O-ring performance. Ashton Seals supplies O-rings in a wide range of elastomers to suit different pressures, fluids, and temperatures.
Common material options:

• Nitrile (NBR): Excellent resistance to oil and fuel; ideal for hydraulic and pneumatic systems.
• Viton (FKM): Outstanding chemical and temperature resistance; perfect for automotive and industrial environments.
• EPDM: High resistance to water, steam, and brake fluids; suitable for water-based systems.
• Silicone (VMQ): Flexible and stable across extreme temperature ranges.

HNBR: Enhanced durability for demanding environments involving high pressures or aggressive media. Visit our O-rings page to explore the full range of materials and specifications.

Why choose Ashton Seals?

With a history dating back to 1866, Ashton Seals is a trusted name in sealing technology. Our expertise ensures customers receive high-quality, precision-engineered sealing solutions tailored to their operational needs.
Our advantages:

• Comprehensive range of materials and sizes.
• Strict quality assurance and testing standards.
• Expert technical support and guidance.
• Reliable supply chain and responsive customer service.

From standard O-rings to advanced sealing products like X-rings, we provide dependable solutions that deliver long-lasting performance.

Final thoughts

O-rings may be simple in design, but their role in ensuring system reliability cannot be overstated. By understanding how they function and selecting the right materials, you can extend equipment lifespan and reduce maintenance downtime.

Ashton Seals combines traditional engineering expertise with modern manufacturing precision to deliver sealing products you can trust - helping you achieve superior sealing performance across every application.

FAQs

1. What is an O-ring and how does it work?

An O-ring is a circular elastomeric seal that sits in a groove (called a gland) and is compressed between two surfaces. This compression creates a tight, leak-proof seal that prevents the escape of fluids or gases. When pressure is applied, the O-ring is forced against the low-pressure side of the gland, which strengthens the seal while the material’s elasticity allows it to return to shape after pressure is released.

2. What are O-rings made of?

O-rings are made from a variety of elastomer materials, each suited to specific operating conditions.

Common materials include:

• Nitrile (NBR) for general-purpose oil and fuel resistance.
• Viton (FKM) for chemical and temperature resistance.
• EPDM for water and steam resistance.
• Silicone (VMQ) for flexibility across wide temperature ranges.
• HNBR for high-pressure and high-durability applications.

The correct material depends on the application’s pressure, temperature, and media type.

3. How are O-rings measured?

• O-rings are measured by their inside diameter (ID) and cross-section (CS).
• The ID determines the ring’s overall size and fit.

The CS defines the thickness, influencing sealing pressure.
Standard measurements follow BS (British Standard) or AS (Aerospace Standard) sizing charts. Using accurate calliper measurements ensures correct replacement and reliable sealing performance.

4. What causes O-ring failure?

Common causes of O-ring failure include:

• Incorrect sizing leading to over-compression or extrusion.
• Chemical incompatibility with the working fluid.
• Excessive temperature or pressure beyond the material’s rating.
• Poor lubrication or contamination.

Selecting the right compound and ensuring proper installation significantly reduces the risk of leaks and premature wear.​