Choosing a compatible lubricant for a known O-ring material is essential to ensure the integrity and safety of the overall application/system.
Enhancing an O-ring’s performance, and as part of maintenance plans, lubricating is an essential element; however, with numerous greases and lubricants to choose from, it’s imperative that you opt for the most suitable lubricant for the O-ring type and material in place.
Offering a vast O-ring range at SSP, we provide high-quality O-rings and gaskets in various materials, styles, and sizes to cater to all applications and industry systems.
In this post, we look at material compatibility in more detail and the most suitable lubricants and greases for the O-ring type.
O-ring Lubricant
O-rings are primarily designed to seal and fill the space between two mating joints, and when these joints are compressed, the O-ring will provide a robust sealing solution, preventing leaks and contamination.
In order to maintain complete sealability, longevity, minimise friction, and prevent degradation, o-ring grease and lubricants are used.
However, it is essential that you opt for the right lubricant that matches the system it is intended for, to ensure that the application continues running at its optimal performance.
For example, grease lubricants are most suitable for applications operating at low speeds and at relatively stable temperatures.
In comparison, silicone oil applications are more suitable for applications operating at high speeds and high temperatures.
Benefits of silicone grease on O-rings
When looking for a suitable o-ring sealant, consider:
- Stability
- Temperature range
- Water resistance
- Consistency
- Chemical compatibility.
Considering these factors and building them into your decision-making will help to ensure you reap the benefits that the right lubricant can provide, benefits such as:
- Offers protection against wear and tear (due to friction), extending the o-ring’s lifespan.
- Protects the overall application from abrasion as friction is reduced.
- Easier to use and install.
- Have low volatility.
- Good in extreme temperatures and can maintain stability in high temperatures.
- Can improve the low-temperature sealing properties of a material.
- It can prevent blown seals from damaging the application.
Silicone grease for O-rings
O-ring materials vs lubricant types, lubricant and elastomer compatibility.
| Lubricant type O ring material | Silicone grease | PTFE grease | Petroleum grease | Lithium grease | Fluorosilicone grease |
| NBR | Compatible (offers excellent water resistance, reduces friction, and prevents cracking) | Compatible (won’t degrade or swell as PTFE is chemically inert) | Conditional (resistant to petrochemicals, however, important to note compatible with most petroleum oils and greases) | Not compatible (rubber will break down over time) | Compatible (reduces friction and offers good moisture protection) |
| EPDM | Compatible (prevents degradation and swelling, offers watertight seal) | Compatible (chemically suitable) | Not compatible (no chemical compatibility, causing swelling, loss of elasticity, and seal failure) | Not compatible (rubber will swell and lose its sealing properties) | Compatible (offers excellent lubrication to prevent swelling and degradation) |
| FKM (Viton) | Compatible (extends lifespan, compatible with material, prevents cracking) | Compatible (reduces friction, prevents degradation and swelling) | Conditional (good chemical and thermal resistance, but depending on application requirements, there may be a more appropriate lubricant) | Compatible (safe for use as FKM is resistant to petroleum-based greases) | Compatible (reduces friction and offers good lubrication) |
| Silicone (VMQ) | Not compatible (chemically incompatible, causing O-ring to lose structural integrity) | Compatible (rubber safe and prevents dry out) | Not compatible (will cause silicone to swell and lose its structural integrity) | Not compatible (cause a chemical reaction, o ring will warp and swell) | Compatible (good overall compatibility) |
| FFKM | Compatible (offers resistance to chemicals and solvents) | Compatible (chemicals will not react with one another) | Compatible (good chemical resistance) | Not compatible (not recommended for long term use as will lead to seal failure) | Not compatible (significant swelling can occur due to both materials being heavily fluorinated) |
| HNBR | Compatible (supports easier installation) | Compatible (prevents swelling and degradation) | Compatible (HNBR is resistant to petroleum based oils and grease) | Compatible | Compatible (offers thermal stability and a robust sealing solution) |
Critical compatibility warnings
Three of the most common mistakes when choosing lubricants for O-rings to be aware of:
- Can silicone grease damage O-rings? Yes, silicone grease must not be used on silicone O-ring types: VMQ, MQ, PMQ, or FVMQ. Silicone-on-silicone causes absorption and swelling, leading to seal failure. Use fluorosilicone grease for silicone O-rings.
- Petroleum and mineral greases damage EPDM. EPDM O-rings in contact with mineral oil swell, degrade, and lose sealing ability. Use only EPDM-compatible lubricants (silicone-based or specific synthetic options).
- WD-40 is a solvent, not a lubricant. It evaporates and can dry out elastomers. Never substitute WD-40 for proper O-ring lubricant.
Industrial application examples
Silicone grease is found in most industrial applications, such as:
- Hydraulic and pneumatic system seals
- Sanitary process equipment (food production, dairy, brewing, pharmaceutical)
- Petrochemical pipeline connections
- Aerospace and defense sealing
- High-temperature industrial process equipment
- Water treatment system fittings
Temperature range guidance
When considering what is a good lubricant for rubber o-ring systems, you must take into account the temperature ranges of the systems and applications in order to assess material compatibility.
For example:
- MolyKote, high-temperature silicone grease: typically -40°C to +200°C (formulation dependent)
- PTFE-based grease: typically -50°C to +260°C
- Petroleum or mineral grease: typically -20°C to +120°C
- Loctite, lithium grease: typically -30°C to +130°C
- Molykote, fluorosilicone grease: typically -50°C to +175°C
WRAS-approved food grade
O-rings are used within food applications and systems and fall under various compliance regulations and guidelines.
WRAS (Water Regulations Advisory Scheme) is the UK body for approval of portable water contact, i.e., it is the leading certification body for all plumbing products (including O-rings) that are used to connect public water supplies (NSF approval applies to international use).
This means that all o-rings and food-grade o-ring lubricants must be suitable to ensure safety in terms of preventing harmful chemicals and contamination in systems.
The suitable food-grade O-ring lubricant to achieve and meet food-grade safe regulations is PDMS.
Polydimethylsiloxane is a silicone grease with WRAS certification. This lubricant is clear, non-toxic, inert, and non-flammable, making it suitable for systems that fall into this category.
It’s also important to note that Sanitary 3-A Certification standards are applicable to dairy applications and required to ensure that all equipment meets set criteria. This means ensuring the lubricants used are non-toxic, easy to clean, and can be regularly inspected.
Reapplication and maintenance
O-ring maintenance is essential to ensure continued high levels of performance and longevity.
Lubrication helps to meet these criteria and should be carried out before installation of the o ring.
Only a small amount of lubricant is required to provide a thin layer to offer the best protection.
During O-ring maintenance checks, you should always clean the O-ring first before reapplying any lubricant.
If you are installing a new o-ring or replacing an old one, it is recommended that you use your fingers to spread a thin layer of lubricant evenly around the o-ring.
FAQ
Question: Can I use silicone grease on rubber O-rings?
Answer: Yes. This specific type of lubricant is most suitable for rubber O-rings, providing a protective thin layer that helps to prevent cracking and the rubber seal from drying out.
Question: Why can I not use silicone grease on silicone O-rings?
Answer: This is not recommended due to chemical incompatibility, causing the O-ring to lose structural integrity and overall effectiveness.
Question: What is a food-grade O-ring lubricant?
Answer: Food-grade lubricants should be non-toxic, odourless, and tasteless. The most popular food-grade lubricant is PDMS (polydimethylsiloxane) due to its transparency, non-toxic, and non-flammable properties.
Question: How often should O-rings be re-lubricated?
Answer: This is dependent on the application in which the O-ring is placed; however, we recommend that for static seals, lubrication as part of maintenance checks should take place annually, with those placed within dynamic applications lubricated every 3 to 6 months.
Question: Can I use WD-40 on O-rings?
Answer: No, as WD-40 is a petroleum-based product, it can cause problems such as swelling and drying out of the O-ring.
For a range of specialist sealing products to meet your application and system requirements, speak to a member of the SSP team today and see how our high-quality products can help you.
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