Specified NBR requirement
Share the drawing, dimensions, compound designation, specified hardness and required documentation. An NBR material name alone does not identify the complete product specification.
BY MATERIAL
NBR (Buna) O-Rings — Supply & Application Support
We supply NBR O-rings and support compound and application review. Start with your drawing, dimensions, compound or hardness requirement, existing part reference or seal replacement concern.
Request a Technical Review
Initial response within 12 hours.
01 / NBR REQUIREMENTS
Start with Your NBR Requirement
Replacing an existing seal
Include the existing compound or part reference, service history and reason for replacement. An alternative is not assumed equivalent simply because it is also NBR.
Know the media, but not the material?
Share the exact oil or fluid designation, additives, mixtures and operating conditions. Broad labels such as hydraulic oil or lubricating oil do not establish compatibility with a particular compound.
02 / NBR REQUIREMENTS
Review the Compound, Media and Sealing System
NBR Material Characteristics
NBR (nitrile rubber, also known as Buna-N) is an elastomer based on acrylonitrile and butadiene. It is often considered for O-ring seals used with selected mineral oils and greases, provided that the compound and operating conditions are suitable.
NBR compounds can offer useful mechanical and wear characteristics, but performance varies with formulation and service conditions. Conventional NBR may require particular caution where ozone, sunlight or prolonged weather exposure is involved.
ACN Content and Compound Selection
Acrylonitrile (ACN) content influences the balance between oil or fuel resistance and low-temperature flexibility. Higher ACN content generally favors resistance to certain oils and fuels, while lower ACN content can improve flexibility at low temperatures. Neither tendency establishes the operating limits of a finished O-ring.
Fillers, plasticizers and curing systems can also affect compound performance. Two NBR O-rings with the same nominal hardness or dimensions should not be assumed interchangeable. The original material specification, tolerances, service media and application conditions should be reviewed before selecting a replacement.
Fluid Compatibility and Application Conditions
Selected mineral-oil-based lubricants and hydraulic fluids are common starting points for NBR screening. However, hydraulic fluids may include mineral-oil-based, water-containing and synthetic fire-resistant formulations that require different compatibility assessments. Fuel suitability also depends on composition, particularly aromatic content and alcohol blends.
Confirm the exact fluid designation, additives, mixing ratios, temperature and exposure duration, including contact with water, cleaning agents and assembly lubricants. Compatibility assessment should consider swelling or shrinkage as well as changes in hardness and mechanical properties. General compatibility charts do not replace a review of the proposed compound under actual operating conditions.
Sealing Design and Material Alternatives
Static and dynamic sealing applications place different demands on an O-ring. Moving seals require additional review of motion type, speed, surface finish, friction and lubrication. Pressure capability also depends on gland geometry, compression, extrusion clearance and the selected compound. Material name or hardness alone does not establish a high-pressure rating.
If leakage occurs during cold start or repeated service, review the compound's low-temperature behavior alongside fluid exposure, compression history, installation and gland dimensions. HNBR or FKM may be worth evaluating when specific thermal, environmental, mechanical or fluid requirements justify comparison. Any proposed replacement must still be verified against the complete application.
03 / REVIEW
Share What You Already Have
You do not need a complete specification to begin.
- 01
Drawing, inside diameter, cross-section, units and tolerances, where available.
- 02
Specified NBR compound, hardness requirement, existing part reference and required documentation.
- 03
Exact oil or fluid name, additives, mixtures, concentration and cleaning exposure.
- 04
Continuous operating and cold-start temperatures, short exposures, duration, frequency and temperature cycling.
- 05
Pressure, static or dynamic operation, gland details, service history and any leakage or replacement concern.
04 / RELATED PATHS
Continue the technical discussion
05 / TECHNICAL REVIEW FAQ
NBR O-Ring Technical FAQs
What is NBR (Buna-N), and is the material name enough to specify a replacement?
NBR is nitrile rubber, commonly known as Buna-N. It describes a material family rather than a complete compound specification. A replacement review should consider dimensions and tolerances, the original compound or part designation, hardness requirements, fluid exposure and operating conditions. A matching material name, appearance or nominal hardness alone does not establish equivalence.
Are NBR O-rings suitable for hydraulic oils, fuels and lubricants?
NBR is often considered for selected mineral oils, greases and certain hydraulic fluids, but compatibility cannot be confirmed from broad labels such as "hydraulic oil" or "fuel." Water-containing or synthetic fire-resistant hydraulic fluids, aromatic-rich fuels and alcohol blends may require different compound assessments. The exact fluid designation, additives, mixture composition, operating temperature and exposure duration should be reviewed before selecting a grade.
What should be checked if an NBR seal leaks during cold start?
Cold-start leakage may involve reduced low-temperature flexibility or recovery, compression history, fluid-related dimensional changes or sealing-system conditions. Check the minimum temperature, cold-soak duration, start-up pressure and motion, existing compound, seal and gland dimensions, and whether leakage stops after warming. The cause should not be assigned to the material without reviewing these factors. A TR10 or brittleness value alone does not establish the minimum temperature for reliable sealing.
When should HNBR or FKM be considered instead of NBR?
NBR can remain a suitable choice when the selected compound meets the application's fluid, temperature, mechanical and sealing requirements. HNBR may be considered for certain thermal, ozone or mechanical demands, while FKM may be worth evaluating for selected higher-temperature, oil, fuel or chemical exposures. Neither material is an automatic upgrade. Fluid compatibility, cold-start conditions, seal design and the proposed compound must be reviewed before replacement.
Can NBR O-rings be used in dynamic or high-pressure sealing applications?
NBR O-rings may be considered for certain dynamic or pressurized sealing applications, but suitability depends on the complete sealing system. Important factors include motion type, speed or stroke, lubrication, surface finish, pressure, temperature, gland geometry and extrusion clearance. Back-up rings may need consideration where extrusion is a concern. Nominal hardness or material designation alone does not confirm pressure capability, dynamic life or rapid gas decompression (RGD) resistance.
NEXT STEP
Discuss Your NBR O-Ring Requirement
Send the information available. We will review the specification, media and application, and clarify the next information needed.
Request a Technical Review
Initial response within 12 hours.