O-ring knowledge base
Practical guides, material comparisons, and solutions to common sealing-ring problems for maintenance engineers and procurement teams.
Showing all 33 articles
Radial shaft seal vs O-ring: what's the difference and when to use which
A radial shaft seal (oil seal) seals a rotating shaft with a spring-loaded lip and has three dimensions (d × D × b); an O-ring seals by cross-section squeeze in a groove, has two dimensions (ID × CS) and belongs in static and slow dynamic joints. Construction, pressure and speed limits, typical failures — and when to use which.
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- Author
- Ing. Filip Meheš
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O-ring testing standards explained: how to read service life from a material certificate
Compression set, heat ageing, fluid-immersion volume change and hardness — four measurements that decide an O-ring's service life. We explain ISO 815, ISO 188, ASTM D471 / ISO 1817 and ISO 48 so you can read reliably from a material certificate whether the seal will last.
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- Author
- Ing. Filip Meheš
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O-ring or flat gasket: when to use which sealing element
A practical guide to when a static joint is sealed best by an O-ring in a groove, and when the right answer is a flat sheet gasket, a PTFE-envelope gasket or a spiral-wound gasket. The decision is driven by flange type, surface finish, pressure and re-use — referencing ISO 3601-2 for O-ring cavities and EN 1514 for flat gaskets on PN flanges.
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- Author
- Ing. Filip Meheš
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O-ring colours and markings: what black, green, blue, white and brown seals really mean
The colour of an O-ring almost never tells you its material — most elastomers are made in many colours. We explain why black is the default, when blue and white signal food and pharma, what contrast colours are for, and why the ISO 1629 designation is the only reliable identifier.
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- Author
- Ing. Filip Meheš
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O-ring swell and shrinkage in oils and solvents: acceptable limits and predicting material compatibility
O-ring swell up to 15 % is acceptable in good applications, but shrinkage of any magnitude causes immediate leakage. Learn how to measure swell per ISO 1817, understand compatible materials, and design grooves with safety margin.
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- Ing. Filip Meheš
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O-Ring Installation Mistakes and How to Prevent Them
Most O-ring leaks in the field stem from assembly mistakes — incorrect squeeze, sharp edges, insufficient lubrication, and ignored material swell. High risk can be dramatically reduced by following ISO 3601-2 and a simple field checklist.
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- Author
- Ing. Filip Meheš
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Low-temperature and cryogenic O-rings: brittleness, Tg and material choice from −40 to −60 °C and below
In the cold a seal fails sooner than in the heat — the ring hardens, loses elasticity and stops pushing back. We explain the glass-transition temperature (Tg), brittleness and the ISO 812, ASTM D746 and TR10 standards, and which elastomers (VMQ, FVMQ, EPDM, special FKM) stay flexible down to −40 to −60 °C — and where only PTFE will do.
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- Author
- Ing. Filip Meheš
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O-ring compression set: causes, the test, and how to avoid it
Compression set is when an O-ring stays flattened and stops sealing. What causes it, how ISO 815 and ASTM D395 measure it, which materials resist it, and how to design it out.
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- Author
- Ing. Filip Meheš
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O-ring extrusion and blow-out under high pressure: physics, back-up rings, and ISO 3601-2 groove design
Extrusion is a characteristic high-pressure failure mode. Understanding the physics (pressure × diametral gap × Shore hardness) and using PTFE back-up rings or higher-hardness O-rings per ISO 3601-2 groove rules safely prevent it.
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- Author
- Ing. Filip Meheš
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High-temperature O-rings (150–200 °C and above): which elastomer and why
A practical guide to choosing the O-ring material for 150–200 °C and above. Continuous versus peak temperature, the real-world limits of FFKM, VMQ, FKM, HNBR and EPDM, thermal ageing per ISO 188 and hot compression set per ISO 815 — including the answer to “O-ring 200 degrees, what material”.
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- Author
- Ing. Filip Meheš
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PN/ČSN 02 9281: which O-ring replaces this old standard?
PN/ČSN 02 9281 is a cancelled Czechoslovak standard for static O-rings. Learn what its size code means, why it is not an ISO 3601 ring, and how to choose a modern replacement.
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- Author
- Ing. Filip Meheš
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O-rings for drinking water: certifications and materials
Which O-ring and seal approvals actually count for potable water — WRAS, UBA/KTW-BWGL, DVGW W270, NSF/ANSI 61 and 372, ACS — and why EPDM is the default elastomer.
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- Author
- Ing. Filip Meheš
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Seals for food and pharma: certifications and material selection
Seals for food and pharma: which certifications (FDA, EC 1935/2004, USP Class VI, 3-A) you really need and when to choose VMQ, EPDM, PTFE or FFKM.
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- Author
- Ing. Filip Meheš
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O-ring failure analysis: the most common failure modes
From the look of a failed ring you can almost always read the cause. A tour of the most common failures — chemical attack, thermal degradation, extrusion, compression set — and how to prevent them.
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- Author
- Ing. Filip Meheš
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NBR vs FKM (Viton): which O-ring material to choose
NBR or FKM? A head-to-head O-ring decision guide on temperature, media and cost — when nitrile is enough, when Viton pays off, and when neither is the right answer.
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- Author
- Ing. Filip Meheš
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Shore A hardness of O-rings: why 70 is the standard and when to choose another
Shore A hardness decides sealing and extrusion resistance. Why 70 ShA is the standard, when to pick 50 or 90, and how hardness changes in service.
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- Author
- Ing. Filip Meheš
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NBR material — a guide for O-ring seals
NBR (acrylonitrile-butadiene rubber) is the most common O-ring material for contact with mineral oils and fuels. Properties, temperatures, applications.
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- Ing. Filip Meheš
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AS568, ISO 3601 and JIS B 2401: converting O-ring sizes between standards
AS568 dash numbers, ISO 3601 codes and JIS B 2401 series converted to millimetres: cross-section tables, an AS568-214 example and a safe substitution procedure.
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- Author
- Ing. Filip Meheš
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How to measure and identify an unknown O-ring
From two dimensions — inner diameter and cross-section — you can identify almost any O-ring. A guide to measuring and matching to the AS568, ISO 3601 and JIS B 2401 standards.
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- Author
- Ing. Filip Meheš
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Radial shaft seals (oil seals): types, materials and selection
A radial shaft seal seals a rotating shaft. We explain the DIN 3760 types, the materials and their speed limits, the d×D×b dimension, and the key operating requirements when selecting one.
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- Author
- Ing. Filip Meheš
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How to choose the right O-ring material
Medium, temperature, pressure and motion — the four questions that decide a seal material. A practical decision path across the 15 most common elastomers.
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- Author
- Ing. Filip Meheš
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Static vs dynamic sealing: the difference that decides groove, hardness and material
Static vs dynamic seals: 22 % vs 10 % squeeze, harder compounds under pressure, and the point where the radial shaft seal takes over. A practical guide.
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- Author
- Ing. Filip Meheš
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O-ring groove design to ISO 3601-2 — squeeze and gland fill
O-ring groove design to ISO 3601-2: how much squeeze for static and dynamic seals, why gland fill must never reach 100 %, and the design mistakes that cause leaks.
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- Author
- Ing. Filip Meheš
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Radial shaft seal failure analysis — 13 typical failure modes
Radial shaft seal failure analysis: 13 typical failure modes — how to identify each from the lip and the shaft, and when FKM, HNBR or PTFE is the fix.
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- Author
- Ing. Filip Meheš
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Polyurethane (PU/AU) seals — abrasion resistance for hydraulics
Polyurethane (PU/AU) offers the best abrasion resistance of any elastomer. When it beats NBR in hydraulics, and where hydrolysis and temperature rule it out.
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- Author
- Ing. Filip Meheš
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FFKM (perfluoroelastomer) — the premium seal for extreme temperatures and chemicals
FFKM (perfluoroelastomer) combines near-PTFE chemical resistance with rubber elasticity. Rated to 260 °C — when it beats FKM and how availability works.
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- Author
- Ing. Filip Meheš
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EPDM material — a guide for O-ring seals
EPDM (ethylene-propylene-diene rubber) is the go-to choice for water, steam, brake fluid and outdoor applications. Properties and limitations.
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- Ing. Filip Meheš
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How to read an O-ring chemical compatibility chart
A compatibility chart tells you whether a material survives a given medium. We explain the four-tier rating scale, what swell percentages mean, and how to use the chart correctly.
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- Author
- Ing. Filip Meheš
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How to choose a material for hydraulic seals
A step-by-step decision framework for choosing an O-ring material for hydraulic applications — from working fluid to dynamics.
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- Author
- Ing. Filip Meheš
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HNBR — when NBR isn't enough: hydrogenated nitrile in practice
HNBR handles +150 °C continuously and resists ozone and mineral oils. When the 3x price over NBR pays off — and when to step up to FKM. A practical guide.
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- Author
- Ing. Filip Meheš
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PTFE (Teflon) O-rings and seals — where they work and where they don't
PTFE (Teflon) O-rings resist virtually all chemicals from -200 to +260 °C — but they have no elasticity. Where PTFE works, and when to choose FFKM instead.
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- Author
- Ing. Filip Meheš
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Silicone O-rings (VMQ) — properties, limits and applications
Silicone O-rings (VMQ) handle -60 °C to +200 °C and carry FDA and EC 1935/2004 approvals. Where silicone excels, where it fails, and when to pick EPDM or FVMQ.
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- Author
- Ing. Filip Meheš
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FKM (Viton®) — the complete O-ring material guide
FKM (Viton) handles -20 to +200 °C, hot oils, fuels and acids. When it beats NBR, where it fails, and how to pick the right grade, hardness and colour.
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- Author
- Ing. Filip Meheš
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Standard sizes & dimension tables
Need a specific size? Browse the normative O-ring dimension tables — every row links straight to a stocked product.