When it comes to hydraulic or pneumatic quick couplings, the seal ring (also known as the O-ring or gasket) plays a critical role in ensuring a leak-free and reliable connection. While often overlooked, the seal material must be carefully selected based on the fluid type, temperature, and operating environment.
In this post, we’ll walk you through the most common seal ring materials, where they’re used, and how to choose the right one for your quick couplings.
Why Seal Rings Matter
Quick couplings rely on internal seals to:
- Prevent fluid leaks
- Withstand system pressure
- Resist degradation from temperature, chemicals, or friction
- Maintain performance over time
A seal failure can cause leaks, equipment damage, contamination, or even safety hazards—especially in high-pressure systems.
Common Seal Ring Materials and Their Properties
Here’s a breakdown of the most frequently used seal ring materials in quick couplings:
1. NBR (Nitrile Butadiene Rubber)
Also Known As: Buna-N
| Property | Value |
|---|---|
| Temperature Range | -30°C to +100°C (-22°F to +212°F) |
| Fluid Compatibility | Petroleum oils, hydraulic fluids, water |
| Not Suitable For | Strong acids, ozone, brake fluid, ester-based fluids |
| Applications | General-purpose hydraulics, water-based systems, low-cost applications |
Best for: Standard hydraulic systems using mineral oil or water-glycol fluids.
2. FKM (Fluorocarbon Rubber)
Also Known As: Viton®
| Property | Value |
|---|---|
| Temperature Range | -20°C to +200°C (-4°F to +392°F) |
| Fluid Compatibility | Hydraulic oils, fuels, solvents, acids |
| Not Suitable For | Skydrol, low-temperature environments |
| Applications | High-temperature systems, fuel systems, aggressive chemical environments |
Best for: Aerospace, automotive, and high-temp hydraulic systems.
3. EPDM (Ethylene Propylene Diene Monomer)
| Property | Value |
|---|---|
| Temperature Range | -40°C to +150°C (-40°F to +302°F) |
| Fluid Compatibility | Water, steam, brake fluid (glycol-based) |
| Not Suitable For | Mineral oil, fuel, petroleum-based fluids |
| Applications | Water systems, steam, and brake systems |
Best for: Water systems or applications with glycol-based brake fluids.
4. PTFE (Polytetrafluoroethylene)
Also Known As: Teflon®
| Property | Value |
|---|---|
| Temperature Range | -50°C to +260°C (-58°F to +500°F) |
| Fluid Compatibility | Almost all fluids and gases |
| Not Suitable For | Dynamic sealing (low flexibility) |
| Applications | Extreme chemical resistance, static seals, food-grade applications |
Best for: Harsh chemicals, high-temp environments, or FDA-compliant applications.
5. HNBR (Hydrogenated Nitrile Rubber)
| Property | Value |
|---|---|
| Temperature Range | -30°C to +150°C (-22°F to +302°F) |
| Fluid Compatibility | Petroleum oils, refrigerants |
| Not Suitable For | Strong acids, steam, polar solvents |
| Applications | Refrigeration, automotive, high-wear hydraulic systems |
Best for: Durable, oil-resistant applications in automotive or industrial use.
6. Silicone Rubber
| Property | Value |
|---|---|
| Temperature Range | -60°C to +230°C (-76°F to +446°F) |
| Fluid Compatibility | Air, water, some chemicals |
| Not Suitable For | Oils, fuels, steam |
| Applications | Medical, food-grade, vacuum systems |
Best for: Clean, low-pressure environments, especially with food or pharmaceuticals.
Quick Seal Material Selection Guide
| Application Area | Recommended Seal Material |
|---|---|
| Standard Hydraulics | NBR |
| High Temp Hydraulics | FKM |
| Water Systems | EPDM |
| Chemical Processing | PTFE |
| Refrigerants/Air Con. | HNBR |
| Food/Pharma Equipment | Silicone, PTFE |
How Are Seal Rings Tested?
Manufacturers conduct a range of tests to ensure seals meet performance standards:
- Compression set test (resilience over time)
- Tensile strength and elongation
- Temperature cycling
- Chemical immersion tests
- Leak and pressure testing inside assembled quick couplings
International standards such as ISO 3601 and SAE AS568 define the dimensions and tolerances for O-rings used in couplings.
Tips for Choosing the Right Seal
- Know your fluid – Check the seal’s chemical compatibility.
- Consider temperature range – Match the operating environment.
- Check for approvals – Food-grade, medical-grade, or high-temperature certifications.
- Don’t mix materials – Always replace seals with the same material unless advised otherwise.
- Storage matters – Keep seals in cool, dry, dark environments to avoid premature degradation.
Final Thoughts
Seal rings may be small, but they’re vital to the performance of any quick coupling. The right material ensures safety, longevity, and optimal system efficiency. Whether you’re working with high-pressure hydraulics, aggressive chemicals, or clean water systems, choosing the correct seal material can make all the difference.
Need help selecting the right coupling and seal for your system? Contact our technical team—we’re here to help match you with the perfect solution for your application.