NBR 90 O-Rings Explained: When to Use Harder Nitrile Seals
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Most O-rings used in engineering and automotive systems are made from NBR 70, the standard hardness nitrile compound.
But when pressure increases or extrusion becomes a risk, a harder O-ring is often required.
That’s where NBR 90 O-rings come in.
With a higher hardness rating, these seals are designed to perform in more demanding environments where softer O-rings may deform or fail.
What Does NBR 90 Mean?
NBR stands for nitrile rubber, one of the most widely used sealing materials thanks to its strong resistance to oils and fuels.
The number 90 refers to the Shore A hardness of the rubber compound.
For comparison:
| Material | Shore Hardness | Typical Use |
|---|---|---|
| NBR 70 | Standard hardness | General sealing |
| NBR 90 | Harder compound | Higher pressure systems |
A harder O-ring resists deformation more effectively, helping prevent extrusion under pressure.
Why Use NBR 90 O-Rings?
Better for Higher Pressure
When systems operate at higher pressures, softer O-rings can deform or extrude into small clearances.
NBR 90 O-rings offer:
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improved extrusion resistance
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stronger sealing under pressure
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greater durability in demanding systems
This makes them particularly useful in hydraulic and mechanical assemblies.
Increased Wear Resistance
The harder compound can also provide better resistance to:
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abrasion
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mechanical wear
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repeated compression cycles
This can help extend the service life of seals in moving assemblies.
Excellent Oil & Fuel Compatibility
Like standard nitrile, NBR 90 performs well with many automotive fluids, including:
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engine oils
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gearbox oils
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hydraulic oils
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diesel and petrol fuels
Because of this, nitrile O-rings remain one of the most common sealing materials across automotive and industrial applications.
Common Uses for NBR 90 O-Rings
Hydraulic Systems
Harder O-rings are often preferred where higher pressures are present, including:
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pumps
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hydraulic fittings
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valve assemblies
Automotive Applications
NBR 90 O-rings are commonly used in systems exposed to oil and fuel, such as:
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engines
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gearboxes
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axle components
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fuel systems
High-Pressure Air Systems
Because of their improved extrusion resistance, NBR 90 O-rings are also used in high-pressure air environments.
Examples can include:
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compressed air systems
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pneumatic equipment
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industrial air systems
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diving equipment such as tank and regulator sealing points
In these environments, the harder compound helps maintain sealing integrity where pressures are significantly higher than typical fluid systems.
As always, the correct specification should be chosen for the exact application.
NBR 90 vs NBR 70
| Feature | NBR 70 | NBR 90 |
|---|---|---|
| Hardness | Standard | Hard |
| Pressure resistance | Moderate | Higher |
| Flexibility | Higher | Lower |
| Extrusion resistance | Moderate | Improved |
For everyday sealing tasks, NBR 70 remains the most common choice.
But when pressure or mechanical stress increases, NBR 90 is often the better option.
NBR 90 O-Ring Sizes at Seal With Selo
We currently stock over 50 NBR 90 O-ring sizes, with the range continuing to expand.
Available in both metric and imperial (BS) sizes, these seals are suitable for a wide range of automotive, hydraulic and industrial applications.
As with the rest of the Seal With Selo range:
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items are supplied from UK stock
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there is no minimum order quantity
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orders ship with same-day dispatch before our daily cut-off
More sizes will continue to be added as the range grows.
In Summary
NBR 90 O-rings offer a tougher sealing solution where pressure, wear or extrusion risk increases.
If your application involves:
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higher pressures
-
oil or fuel exposure
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demanding mechanical environments
then NBR 90 nitrile O-rings may be the correct choice.
Shop here searching for shore 90: Nitrile (NBR) O-Rings – Fuel, Oil & Hydraulic Seals | SealWithSelo – Seal with Seloauto