Direct answer: NBR is often a starting point for many conventional hydraulic-oil applications. FKM may be compared for some fuels, hotter oils, or more demanding fluid exposure. Pneumatic connectors require confirmation of pressure, temperature, oil mist, movement, and the connector specification.
Confirm size and groove first
Measure ID and CS without stretching or squeezing the ring. Inspect the groove, port, fitting, and sealing surface for damage. Follow the measurement guide when replacing a worn seal.
Hydraulic-fitting checks
- Exact hydraulic fluid and additives
- Operating and peak pressure
- Minimum and maximum temperature
- Static or dynamic movement
- Groove clearance and extrusion risk
- Required material and hardness
- Surface condition and installation path
NBR is common in many petroleum-oil systems, but it is not universal. FKM is not automatically suitable for every hydraulic fluid, coolant, or fuel.
Pneumatic-connector checks
- Compressed-air pressure
- Oil mist or lubricant in the line
- Indoor or outdoor exposure
- Temperature cycling
- Connector movement and assembly frequency
- Original connector or equipment specification
Material is only one part of the decision
Pressure can force rubber into a clearance gap, while motion adds friction and wear. Hardness, groove design, surface finish, and backup-ring requirements may be as important as the material family.
Review O-Ring Materials for Fuel, Oil, and Hydraulic Systems, the Chemical Compatibility Guide, and the Hardness Guide.
Choose the buying path
- Size, fluid, material, hardness, and pressure confirmed: search the exact specification or browse small packs.
- Fluid, pressure, groove, connector, or material uncertain: use Bulk Quote.
- Drawing, sample, part number, unusual size, critical equipment, or larger quantity: submit all technical details for review.
What to send
- ID and CS
- Material and hardness if known
- Hydraulic fluid, gas, air, or lubricant
- Temperature and pressure
- Static or dynamic movement
- Connector or fitting part number
- Quantity
- Photo, drawing, sample, or groove measurements
FAQ
Are hydraulic O-rings always NBR?
No. NBR is common, but the exact fluid, additives, temperature, pressure, motion, and equipment specification determine the choice.
When should FKM be compared?
FKM is often reviewed for some fuel, heat, and demanding oil conditions, but compound-specific compatibility is still required.
Can the same O-ring be used in a pneumatic connector?
Not automatically. Confirm size, pressure, temperature, oil mist, movement, and connector requirements.
When is application review necessary?
Request review whenever the fluid, pressure, material, groove, connector, or failure cause is uncertain.
Technical reference: Parker O-Ring Handbook.
