O-rings are among the most widely used sealing elements in hydraulic and pneumatic systems. Their O-ring Pressure Rating, O-ring maximum pressure, and O-ring pressure limits are critical factors that determine reliability under operating conditions. Actual performance depends on multiple variables, including material type, durometer (Shore A hardness), temperature, media compatibility, extrusion gap, and groove design.
This article provides a comprehensive analysis of the pressure ranges for O-rings made from eight common rubber materials across different hardness levels. It serves as a practical engineering reference to help select the right O-ring for your application.
Important Notice:
- The following data are general engineering design reference values applicable to static seals or low-speed dynamic seals.
- The actual pressure-bearing capability must be determined by comprehensively considering factors such as O-ring cross-section diameter, extrusion gap, system temperature, and media type.
- For harsh operating conditions such as high pressure (>20 MPa), high temperature (>100°C), or corrosive media, target bench testing or consulting the seal manufacturer is highly recommended.
- Installing backup rings can significantly improve the anti-extrusion capability of O-rings under high pressure. Generally, adding one backup ring can increase the pressure capacity by 1.5 to 2 times.
1. Nitrile Rubber (NBR) O-rings
When the hardness range of NBR O-rings is 40 to 90±5 Shore A, their working pressure increases with the increase of hardness. Low-hardness O-rings are softer and suitable for low-pressure and low-stress sealing, while high-hardness O-rings are more suitable for high-pressure applications. The following are the reference pressure ranges for NBR O-rings of different hardness:
- Hardness 40±5 Shore A: Suitable for low-pressure applications, typically withstands 1–5 MPa (10–50 bar)
- Hardness 50±5 Shore A: Withstands 5–10 MPa (50–100 bar)
- Hardness 60±5 Shore A: Withstands 10–15 MPa (100–150 bar)
- Hardness 70±5 Shore A: Withstands 15–20 MPa (150–200 bar)
- Hardness 80±5 Shore A: Withstands 20–35 MPa (200–350 bar)
- Hardness 90±5 Shore A: Withstands 35–50 MPa (350–500 bar)
NBR has good oil resistance and is widely used in sealing petroleum-based hydraulic oils, fuels, and other media.
2. Fluorocarbon Rubber (FKM) O-rings
The hardness range of FKM O-rings is 50 to 90±5 Shore A, and their working pressure also increases with hardness. FKM exhibits excellent high-temperature resistance and chemical corrosion resistance, making it suitable for harsh environments. The reference O-ring pressure limits are as follows:
- Hardness 50±5 Shore A: Suitable for low-pressure applications, withstands 5–10 MPa (50–100 bar)
- Hardness 60±5 Shore A: Withstands 10–15 MPa (100–150 bar)
- Hardness 70±5 Shore A: Withstands 15–20 MPa (150–200 bar)
- Hardness 80±5 Shore A: Withstands 20–35 MPa (200–350 bar)
- Hardness 90±5 Shore A: Withstands 35–50 MPa (350–500 bar)
3. Silicone O-rings
The hardness range of Silicone O-rings is 30 to 90 Shore A, and their pressure capability generally increases with hardness. Silicone material is soft with outstanding high and low-temperature resistance, but its mechanical strength and pressure performance are relatively low. Therefore, it is typically suited for low-to-medium pressure situations requiring good elasticity. Reference pressure ranges:
- Hardness 30–40 Shore A: Suitable for extremely low-pressure situations, withstands 1–3 MPa (10–30 bar)
- Hardness 50 Shore A: Withstands 3–7 MPa (30–70 bar)
- Hardness 60 Shore A: Withstands 7–10 MPa (70–100 bar)
- Hardness 70 Shore A: Withstands 10–15 MPa (100–150 bar)
- Hardness 80 Shore A: Withstands 15–20 MPa (150–200 bar)
- Hardness 90 Shore A: Withstands 20–25 MPa (200–250 bar)
4. Ethylene Propylene Diene Monomer (EPDM) O-rings
The hardness range of EPDM O-rings is 40 to 90±5 Shore A, and their working pressure rises as hardness increases. EPDM features excellent weather resistance, ozone resistance, and chemical corrosion resistance. However, its overall O-ring maximum pressure performance is lower than that of FKM and NBR, making it more commonly used in low-to-medium pressure systems. Reference pressure ranges:
- Hardness 40±5 Shore A: Suitable for low-pressure applications, withstands 1–5 MPa (10–50 bar)
- Hardness 50±5 Shore A: Withstands 5–10 MPa (50–100 bar)
- Hardness 60±5 Shore A: Withstands 10–15 MPa (100–150 bar)
- Hardness 70±5 Shore A: Withstands 15–20 MPa (150–200 bar)
- Hardness 80±5 Shore A: Withstands 20–25 MPa (200–250 bar)
- Hardness 90±5 Shore A: Withstands 25–35 MPa (250–350 bar)
Custom EPDM O-ring
5. Hydrogenated Nitrile Rubber (HNBR) O-rings
The hardness range of HNBR O-rings is 55 to 90±5 Shore A, and their working pressure increases with hardness. HNBR outperforms standard NBR in oil resistance, high-temperature resistance, and wear resistance, making it suitable for higher-pressure applications. Reference pressure ranges:
- Hardness 55±5 Shore A: Suitable for low-pressure applications, withstands 5–10 MPa (50–100 bar)
- Hardness 60±5 Shore A: Withstands 10–15 MPa (100–150 bar)
- Hardness 70±5 Shore A: Withstands 15–20 MPa (150–200 bar)
- Hardness 80±5 Shore A: Withstands 20–35 MPa (200–350 bar)
- Hardness 90±5 Shore A: Withstands 35–50 MPa (350–500 bar)
6. Fluorosilicone (FVMQ) O-rings
The hardness range of FVMQ O-rings is 45 to 80 Shore A, and their pressure limits increase with hardness. Fluorosilicone combines the advantages of silicone rubber and fluororubber, offering good high/low-temperature resistance and chemical resistance, though its pressure resistance is usually lower than that of HNBR or FKM. Reference pressure ranges:
- Hardness 45±5 Shore A: Suitable for low-pressure applications, withstands 1–5 MPa (10–50 bar)
- Hardness 55±5 Shore A: Withstands 5–10 MPa (50–100 bar)
- Hardness 65±5 Shore A: Withstands 10–15 MPa (100–150 bar)
- Hardness 75±5 Shore A: Withstands 15–20 MPa (150–200 bar)
- Hardness 80±5 Shore A: Withstands 20–25 MPa (200–250 bar)
7. AFLAS (TFE/P) O-rings
AFLAS is a high-performance material with excellent chemical stability and high-temperature resistance. It belongs to a special type of fluoroelastomer but is not a perfluoroelastomer (FFKM). When the hardness range of AFLAS O-rings is 60 to 90 Shore A, its pressure capability increases with hardness. Reference pressure ranges:
- Hardness 60±5 Shore A: Suitable for medium-pressure applications, withstands 10–15 MPa (100–150 bar)
- Hardness 70±5 Shore A: Withstands 15–20 MPa (150–200 bar)
- Hardness 80±5 Shore A: Withstands 20–30 MPa (200–300 bar)
- Hardness 90±5 Shore A: Withstands 30–40 MPa (300–400 bar)
8. Perfluoroelastomer (FFKM) O-rings
FFKM is one of the most outstanding elastomer materials currently available for chemical and high-temperature resistance, designed for extremely harsh environments. When the hardness range of FFKM O-rings is 75 to 90 Shore A, its pressure capability scales up with hardness. Reference pressure ranges:
- Hardness 75±5 Shore A: Suitable for medium-to-high pressure applications, withstands 20–30 MPa (200–300 bar)
- Hardness 80±5 Shore A: Withstands 30–35 MPa (300–350 bar)
- Hardness 90±5 Shore A: Withstands 35–40 MPa (350–400 bar)
Comprehensive Factors Affecting O-ring Pressure
As mentioned, these pressure ratings are engineering reference values for typical scenarios. The actual O-ring Pressure Rating in your system will be influenced by several variables:
- O-ring Cross-Section Diameter: At the same hardness level, a larger cross-section provides stronger anti-extrusion capabilities.
- Extrusion Gap: The smaller the clearance gap of the sealing groove, the higher the allowable working pressure.
- Operating Temperature: High temperatures reduce the modulus and strength of rubber materials, lowering the O-ring maximum pressure capacity.
- Media Type: Certain chemical media can cause the rubber to swell or degrade in performance.
- Sealing Type: Static seals can typically withstand significantly higher pressures than dynamic seals.
- Backup Ring Configuration: Integrating backup rings drastically enhances anti-extrusion performance and should be prioritized in high-pressure environments.
How Flexiparts Can Support Your Sealing Needs
Understanding complex O-ring pressure limits and selecting the suitable O-ring for extreme environments can be a daunting task. Material type, hardness, and system design all contribute to defining realistic O-ring pressure limits and safe operating boundaries.
Flexiparts, as your trusted engineering partner, specializes in custom rubber and plastic components, including high-performance O-rings tailored to your exact O-ring Pressure Rating requirements. Whether you need standard sizes, custom compounds, or engineered solutions for extreme pressures, temperatures, or chemicals, our team provides full customization, including custom materials matching and hardness optimization, rapid prototyping, custom size, groove design, and anti-extrusion solutions.
Contact Flexiparts today for personalized recommendations, samples, or a full pressure rating evaluation. Let us help you select the right O-ring that delivers reliability, longevity, and value for your hydraulic, pneumatic, or industrial application.
