Factors to Consider When Selecting an O‑Ring

You can have the most innovative, high-tech equipment, but a poorly chosen O-ring can render it inoperable. The right O-ring in both material and size is essential for ensuring reliable performance, safety, and longevity.

Whether you're working in aerospace, oil & gas, or manufacturing, understanding how to select the correct O-ring is critical.

Start with Material Selection

Material selection is your first and arguably most important decision when choosing an O-ring. Different industries and environments demand different material properties.

Here’s a quick reference comparison:

Material	Temp Range (°F)	Strengths	Typical Applications
Nitrile (Buna-N)	-40 to 250	Oil resistance, durability	Automotive, industrial machinery
Fluoroelastomer (FKM/Viton)	-15 to 400	Chemical resistance, heat tolerance	Aerospace, fuel systems
Chloroprene (Neoprene)	-65 to 250	Weather & ozone resistance	HVAC, refrigeration (Freon®)
Silicone	-80 to 450	Extreme temp tolerance, flexibility	Medical devices, lighting seals
Highly Saturated Nitrile (HSN)	-40 to 325	Heat and chemical resistance	Oil & gas, transportation
EPDM	-65 to 300	Steam, water, Skydrol® resistance	Food-grade, aerospace hydraulics
PTFE	-65 to 500	Low friction, chemical inertness	Semiconductor, pharma
Aflas®	+25 to 450	Electrical and chemical resistance	Power generation, chemical processing

Tip: Start by understanding what fluids, temperatures, and movement types your O-ring will be exposed to. Match those variables to the ideal elastomeric material.

Temperature Resistance Matters

Extreme heat or cold can drastically affect O-ring elasticity and sealing performance. 
For example: 

• In cold environments, O-rings can become brittle and crack.
• In high-heat settings, they may soften and degrade over time.

Always cross-reference your working temperature range with the material’s rating to avoid premature failure.

Consider Operating Pressure

• For low to moderate pressures, a standard 70 Shore hardness works well.
• For high-pressure applications (1500+ psi), consider upgrading to a shore hardness of 80–90 to maintain shape under stress.

In dynamic systems like hydraulic pumps or piston cylinders, this change can be a make-or-break decision.

Surface Finish Impacts Longevity

For dynamic sealing applications:

• Ideal finish: 5 to 16 µin RMS
• Static sealing: Up to 64 µin RMS is acceptable

Improper surface finishes can increase friction, leading to premature wear and reduced effectiveness.

 

Understand Stretch and Fit

Your O-ring must sit slightly stretched in its groove to seal properly. Best practices:

• Target stretch: 2% is ideal
• Acceptable range: 1–5%

Over-stretching can distort the O-ring, while under-stretching can cause sealing gaps.

Cross-Industry Examples

Oil & Gas, Petroleum, and Energy

O-rings in these industries must endure extreme temperatures, aggressive chemicals, and high pressures. APG offers materials like Aflas® and FKM that provide excellent resistance to gas, steam, amines, and hydrocarbons – ideal for downhole tools, valves, and refinery equipment.

Semiconductor Manufacturing

Semiconductor processes demand ultra-clean, chemically resistant sealing solutions. APG’s PTFE and FFKM O-rings are designed to perform in plasma etching, wet processing, and vacuum environments where contamination is non-negotiable.

Aerospace

In aerospace, precision and reliability are critical. APG supplies O-rings for use in fuel systems, hydraulic lines, and engine components, using materials like EPDM, and Vitron® that meet stringent temperature and chemical exposure requirements.

Automotive

From fuel injectors and transmission systems to braking components, APG provides Buna-N and HNBR rings that deliver performance under high pressure and constant motion. Our O-rings support both traditional and electric vehicle designs.

Hydraulic Systems

Sealing in hydraulic systems requires strength under pressure. APG's O-rings in NBR, HNBR, and FKM provide robust performance in cylinders, pumps, and valves where high-pressure dynamic motion is present.

Manufacturing

From robotics to automated conveyors, APG’s versatile O-rings help manufacturers maintain uptime by providing dependable seals in equipment exposed to heat, vibration, and abrasive materials.

Construction

Heavy-duty equipment like excavators, concrete pumps, and compressors depend on O-rings that hold up to rough use and weather conditions. APG offers rugged, field-tested sealing options for demanding construction environments.

Chemical Processing

Safety and reliability are essential in chemical processing plants. APG’s chemical-resistant elastomers ensure leak prevention in applications involving caustic fluids, acids and high temperatures.

Pulp & Paper

Wet, abrasive, and chemically treated environments are common in pulp and paper operations. APG supplies EPDM and PTFE O-rings that provide sealing in rollers, pumps, dryers, and chemical dosing equipment.

Conclusion: Choose with Confidence

Choosing the right O-ring is more than just picking a part number. It’s a crucial decision that affects reliability, safety, and performance across nearly every industry.

Next Steps: Let’s Help You Seal the Deal

At APG, we offer a comprehensive selection of standard and vulcanized O-rings in materials for every application. Our technical team is here to guide you through your selection process.

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Need help choosing? Contact an APG Expert