How Compression Set Affects Rubber Gasket Sealing Performance
Compression set is one of the most critical yet often misunderstood factors in rubber gasket design. Even when initial sealing pressure is sufficient, excessive compression set can lead to loss of sealing force, leakage, and premature gasket failure over time.
1. What Is Compression Set?
Compression Set (%) measures the permanent deformation of a rubber gasket after it has been compressed for a specific time and temperature.
Compression Set (%) = (H₀ − H₂) / (H₀ − H₁) × 100
Where:
H₀ = Original thickness
H₁ = Compressed thickness
H₂ = Thickness after recovery
Engineering Meaning: A lower compression set value indicates better elastic recovery and longer sealing life.
2. Why Compression Set Matters in Gasket Applications
- Loss of sealing force under long-term static compression
- Increased leakage risk in low-pressure systems
- Poor rebound after thermal cycling
- Reduced tolerance to flange relaxation and vibration
Important: A gasket with excellent initial sealing pressure but high compression set may fail faster than a softer material with better recovery.
3. Typical Compression Set Values by Material
| Material | Test Condition | Compression Set (%) | Sealing Performance |
|---|---|---|---|
| NBR | 70°C × 22h | 15–30% | Good for oil & fuel |
| EPDM | 100°C × 22h | 20–35% | Excellent weather resistance |
| FKM (Viton) | 150°C × 22h | 10–25% | High-temp sealing stability |
| Silicone (VMQ) | 150°C × 22h | 25–45% | Soft, poor long-term load |
| HNBR | 150°C × 22h | 8–20% | Excellent durability |
4. Real Application Example: Flange Rubber Gasket
Case: Water Pipe EPDM Gasket
- Material: EPDM 70 Shore A
- Initial compression: 25%
- Operating temperature: 60°C
- Service time: 18 months
Observed Issue:
After long-term compression, the gasket thickness recovery dropped by ~30%, resulting in flange leakage despite correct bolt torque.
Solution: Replacing standard EPDM with low-compression-set EPDM compound reduced leakage and extended service life by over 2×.
5. How to Reduce Compression Set in Gasket Design
- Select materials with lower permanent deformation (HNBR, FKM)
- Avoid over-compression (>30%)
- Control operating temperature
- Use proper curing systems and fillers
- Design for flange relaxation compensation
Design Tip: Compression set performance should always be evaluated together with hardness, temperature, and service life-not as a single parameter.
Conclusion
Compression set directly determines whether a rubber gasket can maintain sealing force over time. For long-term static sealing applications, choosing a low compression set compound is often more important than simply increasing hardness or bolt torque.
