What O-Ring Materials Are Used in Press-Fit Systems?

The most common O-ring materials used in press-fit pipe systems are EPDM, FKM and HNBR. The correct material depends on what is flowing through the pipe, operating temperature, pressure, chemical exposure and any certification requirements.

In a press-fit system, the pipe and fitting provide the mechanical connection, while the O-ring creates the pressure-tight seal.

That small elastomer ring can determine whether a joint performs reliably for years — or starts leaking because the seal isn't compatible with the application.

For stainless steel press-fit systems such as Europress, the main seal materials include:

The important point is simple:

Don't choose an O-ring based on the pipe material alone. Choose the seal based on the medium and operating conditions.

What Does an O-Ring Do in a Press-Fit System?

An O-ring is the sealing element inside the press fitting.

When the fitting is pressed onto the pipe, two things happen simultaneously:

1. The fitting is mechanically deformed around the pipe.
2. The O-ring is compressed inside the fitting.

That compression creates the seal between the pipe and fitting.

In a Europress joint, the stainless steel provides the mechanical strength while the elastomer O-ring creates the pressure-tight seal.

So while the O-ring is small, it's doing a critical job.

The pipe carries the load.
The fitting locks the joint together.
The O-ring keeps the medium inside the pipe.

Why Does O-Ring Material Matter?

Not every elastomer reacts the same way to oil, water, chemicals, heat or gas.

An O-ring that works perfectly in a water system may be completely unsuitable for an oil-containing application.

Exposure to an incompatible medium can cause the seal to:

• Swell
• Shrink
• Harden
• Soften
• Crack
• Lose elasticity
• Take a permanent compression set
• Become chemically degraded
• Leak prematurely

That's why O-ring compatibility is a specification issue, not simply a spare-parts issue.

The right seal material depends on the application.

What Are the Main O-Ring Materials Used in Press-Fit Systems?

The three materials most relevant to Europress press-fit systems are:

• EPDM — Ethylene Propylene Diene Monomer
• FKM / FPM — Fluoroelastomer
• HNBR — Hydrogenated Nitrile Butadiene Rubber

Each one has a different set of strengths.

EPDM O-Rings

EPDM is commonly used for water and oil-free compressed air applications.

EPDM has excellent resistance to:

• Water
• Hot water
• Steam
• Ozone
• Weathering
• Ageing

It's therefore widely used in water and utility applications and is a common choice for standard oil-free compressed air systems.

What is EPDM used for?

Typical applications include:

• Potable water
• Cooling water
• Heating systems
• Oil-free compressed air
• Fire protection
• Glycol systems
• Selected chemical applications

What is EPDM not suitable for?

EPDM generally has poor compatibility with:

• Mineral oils
• Petroleum-based oils
• Hydrocarbons
• Many oil-based fluids

That's an important consideration for compressed air.

If your compressor system introduces oil carryover into the compressed air, don't automatically assume the standard EPDM seal is the correct choice.

Check the compressor type, air treatment and manufacturer's seal compatibility requirements.

EPDM temperature range

The allowable temperature depends on the particular Europress seal, application and manufacturer's specifications.

Europress installation guidance lists EPDM at approximately -20°C to 95°C, with short-term spikes up to 120°C. Other technical information may specify different limits depending on the particular seal and application.

Always use the manufacturer's specified temperature rating for the exact fitting and seal being installed.

FKM O-Rings

FKM, also known as FPM and commonly associated with the trade name Viton, is selected when greater resistance to oils, hydrocarbons, chemicals or elevated temperatures is required.

FKM is particularly useful where EPDM isn't chemically compatible with the medium.

Typical applications include:

• Oil-lubricated compressed air
• Oil systems
• Hydrocarbons
• Lubrication systems
• Industrial gases
• Chemical applications
• Higher-temperature services

Europress identifies FKM as an option for oil systems, lubrication, aggressive chemicals, compressed air and higher-temperature water applications.

Why choose FKM instead of EPDM?

The key reason is chemical compatibility.

If the medium contains hydrocarbons or oil, FKM may be a more appropriate elastomer than EPDM.

That doesn't mean FKM is automatically "better".

It means the material is better suited to a different operating environment.

FKM temperature range

Temperature capability depends on the exact FKM compound.

Europress technical information lists FKM seals with an operating range of approximately -20°C to 120°C for the relevant Europress applications, while other manufacturer information may specify higher limits for particular compounds.

Always check the specific product specification rather than applying a generic FKM temperature rating to every fitting.

HNBR O-Rings

HNBR is commonly selected for gas applications and specialised services where mechanical strength, gas resistance and temperature performance are important.

HNBR stands for Hydrogenated Nitrile Butadiene Rubber.

It offers a combination of:

• Good mechanical strength
• Abrasion resistance
• Resistance to gas media
• Improved temperature performance compared with conventional NBR in many applications

Europress identifies HNBR seals primarily for gas applications, including natural gas, liquefied gas and combustible gas installations.

Selected Europress systems also use approved HNBR compounds for certified hydrogen applications.

What is HNBR used for?

Depending on the specific certified system, applications can include:

• Natural gas
• LPG and other combustible gases
• Industrial gases
• Hydrogen
• Other specialised gas services

Gas applications are particularly important because the seal material isn't something you should substitute based simply on physical similarity.

Use the seal specified and approved for the particular pipe system, gas and certification requirement.

EPDM vs FKM vs HNBR: What's the Difference?

Here's the practical comparison.

The colour coding shown here is associated with Europress seal identification. Always confirm the actual seal and application requirements before installation. Europress lists EPDM as black, FKM as green and HNBR as yellow in its installation guidance.

Which O-Ring Is Used for Compressed Air?

For standard oil-free compressed air applications, EPDM is commonly used.

However, the answer changes if oil or other contaminants are present.

Oil-free compressed air

EPDM is commonly suitable.

Oil-lubricated compressed air

FKM may be more appropriate because of its resistance to oils and hydrocarbons.

High-temperature compressed air

The seal needs to be selected according to the actual operating temperature and the manufacturer's specified limits. FKM may be appropriate for higher-temperature applications, depending on the system.

The important point is:

Don't specify the O-ring from the words "compressed air" alone.

Confirm whether the air contains oil, the operating temperature and the exact press-fit system being used.

Which O-Ring Is Used for Gas?

HNBR is commonly used for gas press-fit systems where the specific seal has the required certification for the application.

Europress uses HNBR seals for gas applications including natural gas and combustible gases. Selected systems also use approved HNBR compounds for hydrogen service.

Gas systems have additional safety and certification requirements.

Never substitute an EPDM or FKM seal simply because it physically fits the fitting.

The seal needs to be approved for the particular gas and system.

Which O-Ring Is Used for Water?

EPDM is commonly used for water applications.

It's well suited to water because of its strong resistance to:

• Water
• Steam
• Ozone
• Weathering
• Ageing

For potable water applications, the complete system must meet the relevant approval and certification requirements — not just the O-ring material.

Europress stainless steel systems are available with application-specific seals and certifications for approved water applications.

Which O-Ring Is Best for Oil?

FKM is commonly selected for oil and hydrocarbon applications.

EPDM generally isn't compatible with mineral oils and hydrocarbons, which means choosing EPDM simply because it is the standard seal can lead to premature deterioration.

FKM provides much better resistance to oils and hydrocarbons and is used by Europress for oil and lubrication applications.

Can You Use EPDM Instead of FKM?

Not automatically.

An O-ring can physically fit into the same type of fitting while still being chemically unsuitable for the application.

For example, EPDM may work well in an oil-free compressed air system but be unsuitable where significant mineral oil or hydrocarbon exposure occurs.

That's why replacing one elastomer with another isn't simply a matter of matching dimensions.

You need to match:

• Material
• Medium
• Temperature
• Pressure
• Certification
• Manufacturer approval

If the application changes, check whether the seal material needs to change too.

Can You Use FKM Instead of EPDM?

Again, not automatically.

FKM has excellent chemical and temperature resistance, but that doesn't make it the universal replacement for EPDM.

For example, if you're working on a potable water system, the required approvals and certifications may dictate the appropriate seal material.

Using a more expensive material doesn't necessarily make a system better.

The right O-ring is the one that is compatible with the application and approved for the system.

What Happens If You Use the Wrong O-Ring?

The consequences can range from gradual deterioration to an immediate leak.

Depending on the chemical and temperature exposure, the seal may:

Swell

The elastomer absorbs the medium and increases in volume.

Harden

The material loses flexibility and its ability to maintain an effective seal.

Crack

Chemical attack, heat or ageing can cause the O-ring to develop cracks.

Lose elasticity

The O-ring may no longer recover its original shape after compression.

Take a compression set

The seal remains permanently deformed rather than maintaining the required sealing force.

Leak

Once the seal can no longer maintain contact with the pipe and fitting, the joint can leak.

On a compressed air system, even a relatively small leak can become an ongoing energy loss.

On gas, chemical or process systems, a seal failure can create a much more serious operational or safety issue.

Does O-Ring Material Affect Press-Fit System Lifespan?

Yes, but material selection is only part of the equation.

The lifespan of a press-fit seal depends on:

• Correct elastomer selection
• Operating temperature
• Pressure
• Chemical exposure
• Medium compatibility
• Installation quality
• Pipe preparation
• Fitting condition
• Environmental conditions
• Whether the system remains within its design limits

A correctly specified O-ring can provide long-term sealing performance.

A chemically incompatible O-ring can deteriorate much sooner.

That's why compatibility is more important than simply choosing the most expensive or highest-temperature material.

Do Press-Fit O-Rings Need Maintenance?

Normally, there isn't a routine requirement to remove and replace every O-ring on a correctly installed press-fit system.

The O-ring is enclosed inside the fitting and protected from many external environmental influences.

Europress states that its correctly specified seals are designed for long-term sealing performance and that no routine O-ring replacement schedule is required.

That doesn't mean the entire pipe system should be ignored.

Normal maintenance should still include appropriate inspection for:

• Mechanical damage
• Corrosion
• Leaks
• Vibration
• Changes to operating conditions
• Damage around fittings
• Signs of seal or joint failure

If a fitting is removed, modified or replaced, use the correct replacement seal specified for the system.

Does the O-Ring Need Lubrication Before Pressing?

Don't assume that an O-ring should be lubricated before installation.

The correct installation procedure depends on the specific press-fit manufacturer and system.

Adding an incompatible lubricant can potentially damage the seal or contaminate the system.

For Europress installations, follow the manufacturer's installation instructions and use only approved materials and procedures.

The O-ring should also be checked for:

• Damage
• Correct seating
• Dirt
• Debris
• Contamination

Air Energy's Europress installation guidance specifically identifies checking the O-ring before inserting the pipe as part of the installation process.

Can Press-Fit O-Rings Be Replaced?

Yes, replacement seals are available for press-fit systems, but the replacement needs to be the correct material and size for the fitting and application.

Air Energy supplies O-rings and gaskets for Europress systems, including EPDM, FKM/FPM and HNBR options.

Don't replace a seal based solely on colour or physical dimensions.

Confirm:

1. Fitting size
2. Seal material
3. Application
4. Medium
5. Temperature
6. Pressure
7. Required certification

Does the O-Ring Determine the Pressure Rating?

Not by itself.

The pressure rating of a press-fit system depends on the complete engineered system, including:

• Pipe material
• Pipe wall thickness
• Fitting design
• O-ring
• Press profile
• Pipe diameter
• Operating temperature
• Medium
• Installation method

The O-ring is critical to sealing performance, but you shouldn't calculate a system pressure rating from the elastomer alone.

Always use the manufacturer's published pressure rating for the complete pipe and fitting system.

What Is "Leak Before Press"?

Some press-fit systems use an O-ring design that helps identify fittings that haven't been pressed correctly.

Europress fittings up to 54 mm include a PressCheck sleeve, which provides a visual indication that the fitting has been pressed. Europress also uses a "Leak Before Press" feature on applicable O-rings, allowing an unpressed connection to be identified during pressure testing.

This is an important safety feature because an unpressed fitting can otherwise be difficult to identify after installation.

The idea is straightforward:

If the fitting hasn't been pressed correctly, the system should make that problem easier to find before commissioning.

How Do You Choose the Right O-Ring Material?

Before selecting an O-ring, answer these six questions.

1. What is flowing through the pipe?

Is it:

• Compressed air?
• Water?
• Gas?
• Oil?
• Vacuum?
• Glycol?
• Chemical?
• Hydrogen?

The medium is the starting point.

2. Is oil present?

This is particularly important for compressed air.

Oil-free compressed air and oil-lubricated compressed air can require different seal considerations.

3. What is the operating temperature?

Don't use the maximum temperature of the elastomer in isolation.

Consider the actual continuous operating temperature and any temperature spikes.

4. What pressure will the system operate at?

Pressure needs to be assessed alongside temperature and the complete fitting system.

5. Are chemicals present?

Check compatibility with cleaning agents, process chemicals, hydrocarbons and other substances that may contact the seal.

6. Are there certification requirements?

Gas, potable water, hydrogen and other regulated applications can have specific certification requirements.

The O-ring must be approved for the actual application — not simply physically compatible with the fitting.

O-Ring Selection Example: Compressed Air

Imagine you're specifying a compressed air system for a manufacturing plant.

The compressor produces oil-free compressed air.

The distribution system operates within the specified temperature and pressure limits of the pipework.

In that situation, EPDM may be the appropriate standard seal option, subject to the manufacturer's application requirements.

Now change one detail.

The compressed air system uses an oil-lubricated compressor and there is oil carryover into the distribution network.

The seal selection needs to be reassessed.

This is where FKM may be the more appropriate choice.

The pipe hasn't changed.

The fitting hasn't necessarily changed.

The medium has changed — so the seal requirement has changed.

O-Ring Selection Example: Gas

Now consider a gas installation.

The question isn't simply:

"Will this O-ring seal gas?"

The questions become:

• What gas?
• What pressure?
• What temperature?
• What pipe system?
• What certification is required?
• Which elastomer is approved for that application?

For Europress gas applications, HNBR is used for applicable certified systems.

That's why gas applications should always use the manufacturer's specified seal and approved configuration.

O-Ring Selection Example: Food and Beverage

Food and beverage installations introduce additional considerations.

The pipe may need to cope with:

• Water
• Cleaning processes
• Temperature changes
• Sanitising chemicals
• Compressed air
• Process fluids

Stainless steel may be selected because of its corrosion resistance and suitability for hygienic environments.

But the pipe material is only one part of the system.

The seal material also needs to be appropriate for the medium, temperature and required approvals.

For food-processing projects, don't specify the O-ring based solely on what is commonly used in another industrial application.

Check the exact system documentation.

Are All Press-Fit O-Rings the Same?

No.

This is one of the most important things to understand when specifying press-fit pipework.

Two fittings can look almost identical from the outside while containing different elastomers.

The fitting body might be stainless steel in both cases.

The pipe might be identical.

But the O-ring can be different because the application is different.

For example:

EPDM → water / oil-free compressed air

FKM → oil / hydrocarbons / higher temperatures

HNBR → gas / selected hydrogen applications

That's why seal identification and correct component selection matter during installation and maintenance.

Stainless Steel Press-Fit vs Aluminium Press-Fit: Are the O-Rings the Same?

Not necessarily.

The O-ring is selected as part of the complete piping system, not independently from it.

For Europress stainless steel press-fit systems, different elastomer options are available for different media and applications.

Aluminium compressed air systems such as Unipipe use their own specified sealing components.

You shouldn't assume that an O-ring from one manufacturer's press-fit system can be transferred to another system simply because the dimensions appear similar.

Use the seal specified by the piping system manufacturer.

Common O-Ring Mistakes to Avoid

Mistake 1: Choosing the cheapest seal

A cheaper O-ring isn't cheaper if it fails prematurely.

Mistake 2: Assuming EPDM works for everything

EPDM is excellent for many water and oil-free air applications, but it's not generally suitable for mineral oils and hydrocarbons.

Mistake 3: Choosing FKM because it's "stronger"

FKM isn't automatically better.

The correct elastomer is the one that matches the medium and operating conditions.

Mistake 4: Ignoring oil carryover

Compressed air isn't always oil-free.

Check the compressor type and air treatment before selecting the seal.

Mistake 5: Mixing seals without checking compatibility

Don't substitute an O-ring from another system simply because it fits.

Mistake 6: Ignoring certification

Gas, potable water and hydrogen applications can require specific certified components.

Mistake 7: Reusing damaged seals

If a seal has been damaged, contaminated or compromised during installation, replace it with the correct approved seal.

O-Ring Material Selection: Quick Reference

*Always verify the exact fitting, seal, temperature, pressure and certification requirements for the application.

What Is the Best O-Ring Material?

There isn't one "best" O-ring material for every press-fit application.

EPDM is an excellent choice for many water and oil-free compressed air applications.

FKM is better suited to many oil, hydrocarbon and higher-temperature applications.

HNBR is commonly used for gas and selected hydrogen applications where the relevant system is certified.

The best seal is therefore the one that is chemically compatible, temperature compatible, pressure compatible and approved for the application.

The Bottom Line

The O-ring may be one of the smallest parts in a press-fit fitting, but it has a critical job.

The wrong O-ring can fail even when the pipe and fitting are perfectly installed.

That's why seal selection needs to start with the medium and operating conditions.

As a general guide:

EPDM → water and oil-free compressed air

FKM / FPM → oils, hydrocarbons and higher-temperature applications

HNBR → gas and selected hydrogen applications

But these are starting points — not substitutes for checking the manufacturer's specifications.

For engineered press-fit systems such as Europress, always use the approved O-ring material for the specific application, pressure, temperature and certification requirements.

Need Help Selecting the Right Press-Fit O-Ring?

Air Energy supplies Europress stainless steel press-fit pipe, fittings and replacement O-rings for industrial applications.

We stock application-specific seal options including EPDM, FKM/FPM and HNBR, subject to the relevant fitting and application.

If you're unsure which seal you need, have your pipe size, fitting type, medium, operating pressure and temperature available when you contact us.

Call Air Energy on 1300 99 55 26 or request a quote for the correct Europress O-rings and press-fit components.

Frequently Asked Questions

What O-ring materials are used in press-fit systems?

The most common O-ring materials used in engineered press-fit systems are EPDM, FKM/FPM and HNBR. EPDM is commonly used for water and oil-free compressed air, FKM for oils, hydrocarbons and higher-temperature applications, and HNBR for applicable gas and hydrogen systems.

What is the most common O-ring material for compressed air?

EPDM is commonly used for standard oil-free compressed air applications. If the compressed air contains significant oil carryover or the system operates at elevated temperatures, another elastomer such as FKM may be more appropriate.

Which O-ring is best for compressed air?

For oil-free compressed air, EPDM is commonly suitable. For oil-lubricated compressed air, FKM may be more appropriate because it has better resistance to oils and hydrocarbons. The correct seal must be selected based on the actual compressor, air quality, temperature and manufacturer specifications.

What is EPDM O-ring used for?

EPDM O-rings are commonly used for water, potable water, heating, cooling and oil-free compressed air applications. EPDM has strong resistance to water, steam, ozone and weathering but generally has poor compatibility with mineral oils and hydrocarbons.

What is FKM O-ring used for?

FKM O-rings are commonly used where resistance to oils, hydrocarbons, chemicals or elevated temperatures is required. Applications can include oil systems, lubrication, oil-lubricated compressed air and selected industrial gas applications.

What is HNBR O-ring used for?

HNBR O-rings are commonly used in gas applications because of their mechanical strength and resistance to gas media. Selected certified press-fit systems also use HNBR for hydrogen applications.

Can I use EPDM instead of FKM?

Not automatically. EPDM and FKM have different chemical compatibility. EPDM is generally unsuitable for mineral oils and hydrocarbons, while FKM provides much better resistance to these media. The seal must be selected according to the application and manufacturer specifications.

Can I use FKM instead of EPDM?

Not automatically. FKM is not simply a universal replacement for EPDM. Application approvals, chemical compatibility, temperature, medium and system requirements all need to be considered.

Which O-ring is best for oil?

FKM is commonly selected for oil and hydrocarbon applications because of its strong resistance to these media. The exact seal should still be confirmed against the manufacturer's specifications for the application.

Which O-ring is used for gas?

HNBR is commonly used for applicable gas press-fit systems. The O-ring must be specifically approved for the gas, pressure, temperature and piping system being used.

Which O-ring is used for water?

EPDM is commonly used for water applications because of its excellent resistance to water and steam. Potable water installations also require the complete piping system and seal configuration to meet the applicable approval requirements.

Do press-fit O-rings need to be replaced?

Normally, there is no routine requirement to replace O-rings in a correctly installed press-fit system. However, seals should be replaced if they are damaged, contaminated or if a fitting is being reconfigured and the manufacturer requires a new seal.

Can you replace a press-fit O-ring?

Yes, replacement O-rings are available for press-fit systems. The replacement must be the correct size, material and approved type for the fitting and application.

Do press-fit O-rings need lubrication?

Do not automatically lubricate a press-fit O-ring. Follow the installation instructions provided by the specific manufacturer and use only approved lubricants or installation materials where specified.

What happens if you use the wrong O-ring?

Using an incompatible O-ring can cause swelling, hardening, cracking, loss of elasticity, chemical degradation, compression set and premature leakage.

Does O-ring material affect pressure rating?

The O-ring contributes to sealing performance, but the pressure rating belongs to the complete engineered piping system. Pipe, fitting design, seal, diameter, temperature, medium and installation method all need to be considered.

How long do press-fit O-rings last?

There is no universal O-ring lifespan. Service life depends on the elastomer, medium, temperature, pressure, installation and environment. Correct material selection is critical to achieving long-term sealing performance.

Can press-fit O-rings handle high temperatures?

Some can. FKM generally provides higher temperature capability than EPDM in suitable compounds, but the actual temperature rating depends on the specific seal and system. Always use the manufacturer's published rating for the exact fitting.

Are Europress O-rings interchangeable?

Only use the O-ring specified and approved for the particular Europress fitting and application. Different elastomer materials are designed for different media and operating conditions.

What colour are Europress O-rings?

Europress uses colour identification for its different seal materials. Its installation guidance identifies EPDM as black, FKM as green and HNBR as yellow. Always confirm the seal specification rather than relying on colour alone.

What is Leak Before Press?

Leak Before Press is a feature used in applicable press-fit systems to help identify joints that haven't been pressed correctly. During pressure testing, an unpressed fitting can be identified before the system is commissioned. Europress also uses PressCheck sleeves on applicable fittings as a visual indication of completed pressing.

Related Technical Guides

• How Long Does Press-Fit Pipe Last?
• Stainless Steel Press-Fit vs Welded Pipe Systems
• How Long Does Press-Fit Pipe Last? – Air Energy
• Stainless V Aluminium

Why Choose Air Energy

• Technical Expertise Since 1993: Over 2,000 industrial installations across mining, aquaculture, manufacturing, and remote sites
• Multi-Industry Experience: Experts in compressed air, fuel, water, and process piping systems
• Project Support: Air Energy’s technical team provides guidance to ensure safe, efficient, and long-lasting installations