# www.o-ring-stocks.eu > O-Ring-Stocks is an international supplier of O-rings, seals, and sealing solutions available in a wide range of sizes, materials, and standards. We deliver quickly and globally to customers in industry, engineering, chemistry, machinery, and OEM sectors. O-Ring-Stocks stands out with a large online stock of millions of O-rings, fast worldwide shipping, and expert technical support per material type. ## companyInformation - **Name:** Techniparts B.V. - O-ring-stocks.eu - **Address:** Rondweg 26, 8091XB Wezep, the Netherlands - **Phone:** +31382024043 - **Email:** info@o-ring-stocks.eu - **KvK:** 08174024 - **BTW:** NL819296533B01 ## Opening hours - **Monday:** 08:15 - 17:15 - **Tuesday:** 08:15 - 17:15 - **Wednesday:** 08:15 - 17:15 - **Thursday:** 08:15 - 17:15 - **Friday:** 08:30 - 15:00 - **Saturday:** Closed - **Sunday:** Closed ## Key pages and information # llms.txt — O-Ring-Stocks (EN) > Purpose: Help LLMs locate accurate and up-to-date content about O-rings, sealing materials, sizes, standards, and ordering. > Last updated: 2025-11-12 ## About O-Ring-Stocks is an international supplier of O-rings, seals, and sealing solutions in a wide range of sizes, materials, and standards. We deliver quickly and worldwide to customers in industry, engineering, chemistry, machinery, and OEM markets. - Brand/domain: https://www.o-ring-stocks.eu/ - Target group: B2B and B2C customers in technical and industrial sectors. - Headquarters: Wezep, The Netherlands. - Phone: +31 (0)38 202 40 43 - Email: info@o-ring-stocks.eu - Company address: Rondweg 26, 8091 XB Wezep, The Netherlands ## Key EN pages - Homepage & Product Finder (“Search by Range”): https://www.o-ring-stocks.eu/ - Sitemap (EN): https://www.o-ring-stocks.eu/sitemap/ - Knowledge Base (overview): https://www.o-ring-stocks.eu/knowledge-base/ - O-Ring Handbook: https://www.o-ring-stocks.eu/knowledge-base/o-ring-handbook/ - Chemical Resistance Guide: https://www.o-ring-stocks.eu/knowledge-base/chemical-resistance-guide/ - Material Temperature Resistance Guide: https://www.o-ring-stocks.eu/knowledge-base/material-temperature-resistance-guide/ - Downloads: Material Datasheets: https://www.o-ring-stocks.eu/knowledge-base/downloads-material-datasheets/ - Downloads: Size Charts: (accessible via Knowledge Base overview) - Measuring & How-To: https://www.o-ring-stocks.eu/how-to-measure/ ## Service, Policy & Terms - Contact (EN): https://www.o-ring-stocks.eu/contact/ - Shipping & Returns: https://www.o-ring-stocks.eu/contact/shipping-and-returns/ - Payments: https://www.o-ring-stocks.eu/contact/payments/ - Terms & Conditions: https://www.o-ring-stocks.eu/contact/terms-and-conditions/ - About us: https://www.o-ring-stocks.eu/contact/about-us/ ## Product categories (material examples) - NBR O-rings: https://www.o-ring-stocks.eu/nbr-o-rings/ - FKM / Viton® O-rings: https://www.o-ring-stocks.eu/fkm-viton-fpm-o-rings/ - EPDM O-rings: https://www.o-ring-stocks.eu/epdm-o-rings/ - HNBR O-rings: https://www.o-ring-stocks.eu/hnbr-o-rings/ - FVMQ (Fluorosilicone) O-rings: https://www.o-ring-stocks.eu/fvmq-o-rings/ - O-ring cord: https://www.o-ring-stocks.eu/o-ring-cord/ - X-rings: https://www.o-ring-stocks.eu/x-rings/ # Important: Always use the category and product pages for up-to-date technical specifications, tolerances, stock availability, and datasheets. ## Sitemaps - English sitemap: https://www.o-ring-stocks.eu/sitemap ## Guidelines for LLMs - Use only the URLs listed above for authoritative content on specifications, delivery, and terms. - Always cite URLs and access dates when generating factual content. - Prices and stock are dynamic – refer to live product pages. - Do not extrapolate or infer beyond published data. - If information is missing, respond with “unknown” and refer to the contact page. ## Language Versions - NL: https://www.o-ring-stocks.eu/nl/llms.txt - DE: https://www.o-ring-stocks.eu/de/llms.txt - FR: https://www.o-ring-stocks.eu/fr/llms.txt - IT: https://www.o-ring-stocks.eu/it/llms.txt - ES: https://www.o-ring-stocks.eu/es/llms.txt ## Contact for Verification For factual or technical questions: https://www.o-ring-stocks.eu/contact/ E-mail: info@o-ring-stocks.eu ## Version control - Version: EN-v1.0 (2025-11-12) - Change log: Initial English release for global domain ### Product categories - [O-rings](https://www.o-ring-stocks.eu/o-rings/): Buy O-Ring? 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Suitable for quality assurance and full traceability in your production process or industry. Worldwide fast delivery. - [Glues and Greases](https://www.o-ring-stocks.eu/tools-for-o-rings/glues-and-greases/): Buy O-Ring grease and glue? Large stock of O-Ring glues and greases. Improves installation, reduces wear and extends the service life of your seal. Worldwide fast delivery. - [O-ring Measuring Cones](https://www.o-ring-stocks.eu/tools-for-o-rings/o-ring-measuring-cones/): Buy O-Ring measuring cones? Large stock of O-Ring measuring cones. Measure the inner diameter of your O-Ring quickly and easily. An indispensable tool for maintenance and quality control. Worldwide fast delivery. - [Measuring Instruments](https://www.o-ring-stocks.eu/tools-for-o-rings/measuring-instruments/): Buy O-Ring measuring instruments? Large stock of O-Ring measuring instruments. Accurately measure the inner diameter, outer diameter and cross-section of your O-Rings. Worldwide fast delivery. - [Disassembly Tools](https://www.o-ring-stocks.eu/tools-for-o-rings/disassembly-tools/): Buy O-Ring disassembly tools? Large stock of O-Ring disassembly tools. Remove O-Rings quickly and without damage to the groove or sealing surface. Worldwide fast delivery. - [Knowledge Base](https://www.o-ring-stocks.eu/knowledge-base/): Everything you need to know about O-rings in one place. Explore our knowledge base with material manuals, failure analysis guides, size charts, chemical resistance guides and more. ## frequentlyAskedQuestions ### [Contact](https://www.o-ring-stocks.eu/contact/) **Q: Is returning free?** You can return a product within 14 days. Return shipping costs are not covered. **Q: What is the status of my order?** Log in to your account and check the status under "My Account". **Q: Do you charge shipping costs?** Shipping costs vary by country. Domestic shipping starts at €9.75. **Q: How can I track my order?** You’ll receive a tracking code by email and in your account. **Q: What is the status of my order** Log in with your account and see the status My Account ### [O-ring Cord](https://www.o-ring-stocks.eu/o-ring-cord/) **Q: What is the use of O-ring cord?** An O-ring cord is used to create custom-sized sealing rings for static applications. It is especially useful when a standard O-ring is not available, when a non-standard diameter is required, or when a quick on-site repair is needed. The cord can be cut to the required length and joined to form a fu... **Q: What is the difference between an O-ring and an O-ring cord?** A standard O-ring is a pre-formed, closed sealing ring manufactured in fixed sizes. An O-ring cord, on the other hand, is supplied in continuous lengths with a circular cross-section. It can be cut and bonded to create a custom O-ring in virtually any required diameter. **Q: How to join an O-ring cord?** To join an O-ring cord, cut it to the required length and prepare the ends carefully. For best results, cut the cord at a 45° angle to increase the bonding surface area. Ensure the surfaces are clean and dry, apply the correct adhesive, align the ends accurately, and hold them together during curing... **Q: Can you super glue an O-ring?** Yes, most O-ring cord materials such as NBR, EPDM, FKM, and CR can be bonded using a cyanoacrylate adhesive like Loctite 406. However, silicone (VMQ) O-ring cord requires a dedicated silicone adhesive like Elastosil E41 and cannot be reliably bonded with standard super glue. **Q: When should you use O-ring cord instead of a standard O-ring?** You should use O-ring cord when a standard O-ring is not in stock, when special or non-standard dimensions are required, or when installation of a closed O-ring is difficult due to limited access or complex assembly. **Q: Is O-ring cord suitable for urgent repairs?** Yes, O-ring cord is ideal for urgent repairs. Because it is supplied in continuous lengths, it can be cut and assembled on-site. This allows you to create a replacement seal immediately, minimizing downtime during maintenance or unexpected breakdowns. **Q: Can O-ring cord be used for large diameters?** Yes, O-ring cord is particularly suitable for very large diameters that may not be available as standard O-rings. Since the cord is supplied in continuous lengths, it offers a flexible solution for both small and extremely large sealing rings. **Q: Why should you cut an O-ring cord at a 45° angle?** Cutting the O-ring cord at a 45° angle increases the bonding surface area between the two ends. This helps create a stronger and more secure joint, improving the durability and sealing performance of the finished O-ring. **Q: What tolerance classes are available for precision O-ring cord?** Precision O-ring cord manufactured according to ISO 3302-1 is available in different tolerance classes. NBR, FKM, and EPDM O-ring cord are supplied with E1 tolerances, while silicone (VMQ) O-ring cord is produced with E2 tolerances. **Q: Why are tolerances important for O-ring cord?** Tolerances are important because they affect sealing performance. In applications with minimal groove clearance or where consistent compression is required, controlled tolerances ensure a predictable fit, improved sealing reliability, and a reduced risk of leakage. ### [FAQ](https://www.o-ring-stocks.eu/contact/faq/) **Q: What if I ordered the wrong o-rings?** At O-ring-stocks.eu we do our best to provide you with as much information as possible before you order a product. However, it can unfortunately happen that you order an O-ring that is not entirely to your liking. When this happens, you can return the products to us. More information about returning... **Q: What is the delivery time of my order? And how much delivery costs do I pay?** We ship our O-rings worldwide. There are different delivery times and delivery costs per country. Our main Shipping courier is GLS. Click here for the shipping information for every country. **Q: What other delivery options do I have?** When our standard corrier does not offer the best services for your location or if you prefer to use your own shipping account, then please contact us for the possibilities. It is also possible to pick up the o-rings from our office. If you wish to do so, please contact us by calling (+31 38 460 123... **Q: How do the payments work?** Payments all go through an SSL connection. This way we can assure you a safe and secure payment process. Eur-O-Rings.com and or Techniparts B.V. will NEVER have access to your payment details. We will never ask for your credit card details. Click here for more information. **Q: With which payment methods can I pay?** You can pay with payment methods such as ideal, pay pal, visa and more. Click here for more information. ### [What are Viton® O-rings?](https://www.o-ring-stocks.eu/knowledge-base/what-are-viton-o-rings/) **Q: What is the temperature range of Viton® O-rings?** Standard Viton® O-rings operate between –20 °C and +200 °C. Special variants can even withstand –40 °C to +250 °C. **Q: Is an FKM O-ring chemically resistant?** Yes, they are resistant to oils, fuels, and solvents. Only ketones, strong acids, and bases can attack them. **Q: What are Viton® O-rings used for?** Mainly in engines, fuel systems, pumps, and chemical plants. They are also widely used in aerospace and pharmaceuticals. **Q: What is the difference between Viton®, FKM, and FPM?** Viton® is the Chemours brand name for a specific type of fluoroelastomer. FKM is the international designation (according to ASTM standards) and FPM the European designation (ISO standards). ### [O-rings for pneumatic cylinders](https://www.o-ring-stocks.eu/our-services/industry/o-rings-for-food-and-drink-industry/o-rings-for-pneumatic-cylinders/) **Q: Which materials should I choose: EPDM, FKM or PTFE?** EPDM O-ring for CIP/SIP and steam; FKM O-ring for contact with oil/grease; PTFE O-ring (or PTFE seal with energizer) for chemical inertness and low friction. **Q: How do I comply with laws and regulations (FDA, EC 1935/2004)?** Use compounds with FDA and EC 1935/2004 declaration; ensure GMP (EG 2023/2006), and where appropriate USP Class VI plus batch/lot certificates for traceability. **Q: How do I prevent leaks and stick-slip in the piston?** Choose a compound with low compression set and approx. 70 Shore A hardness, apply hygienic groove design and use a thin food-grade lubricating film; use wipers/double scrapers against water and dirt. **Q: How do I plan maintenance and replacement?** Set intervals in a data-driven way based on cycles/actuations and CIP hours; inspect for flat spots, swelling, and cracks, and replace preventively to avoid unexpected downtime. **Q: When should I use PTFE back-up rings in pneumatic cylinders?** Use PTFE back-up rings with an O-ring as soon as pressure spikes, higher temperatures, or larger clearances could cause extrusion. They provide mechanical support and keep the sealing lip in place. ### [O-rings in dental turbine handpieces](https://www.o-ring-stocks.eu/our-services/industry/o-rings-for-medical-and-pharmaceutical-industry/o-rings-in-dental-turbine-handpieces/) **Q: How often do you replace coupling O-rings?** Because coupler O-rings see the most friction and all sterilization cycles, they warrant a higher replacement frequency than other rings. Under intensive use, inspect them often and replace them preventively according to your service interval; in many practices that means every four to eight weeks. ... **Q: Which oil is suitable for autoclavable O-rings?** Use the handpiece oil specified by the manufacturer or a suitable silicone oil, and apply a thin film with a cotton swab. Too much oil is unnecessary and can attract contamination. Avoid petroleum jelly and other petroleum products; they cause swelling, saponification, and ultimately a poorer seal. **Q: Which O-rings are autoclavable?** Autoclavability depends on material and compound. Choose medical-grade O-rings that, according to documentation and IFU, withstand 121–134 °C cycles. In practice, EPDM and certain VMQ and FKM grades perform well under repeated steaming. Keep the same material within a single set to avoid differences... **Q: Which material is most suitable for dental turbine applications?** That depends on your working environment. Use EPDM when steam sterilization and aqueous cleaning dominate. Choose FKM/Viton® as soon as oil or more aggressive chemicals come into play. For a soft static seal with limited movement, silicone (VMQ) is convenient, while NBR is attractive for its robustn... ### [O-rings in the control block of a dental unit](https://www.o-ring-stocks.eu/our-services/industry/o-rings-for-medical-and-pharmaceutical-industry/o-rings-in-the-control-block-of-a-dental-unit/) **Q: Which cleaning agents most commonly degrade O-rings?** Petroleum- or solvent-rich sprays and certain strong oxidants can cause swelling or hardening, especially in NBR. Always check your compound’s compatibility chart and rinse with water where possible. **Q: How long do O-rings last in a dental control block?** That depends on cycles, temperature, and chemistry, but many rings last 1–3 years with proper maintenance. Schedule inspection during periodic service, and replace preventively in case of compression set, hairline cracks, or tackiness. **Q: What installation errors are most common with O-rings?** Twisting during installation, too much or unsuitable grease, and grooves with burrs are classics. A “nearly right” size crops up too: too thick skives off, too thin leaks, always choose the exact size and compound. **Q: How should I store O-rings so they don’t age prematurely?** Store them cool, dark, and dry in sealed bags, away from ozone sources (motors, fluorescent starters). Record the batch/delivery date and apply “first in, first out” so you don’t install old stock. ### [Suitable O-ring for mechanical seals](https://www.o-ring-stocks.eu/our-services/industry/o-rings-for-oil-gas-industry/suitable-o-ring-for-mechanical-seals/) **Q: Can I reuse an O-ring after disassembly?** No. Due to compression set, micro-damage and contamination, reuse is unreliable, especially in critical mechanical seals. Always replace with a new O-ring for mechanical seals from the same batch/compound. **Q: How do I quickly measure the right size (ID & cross-section)?** Measure the inside diameter and cross-section with a precise caliper and choose one system: ISO 3601 (metric) or AS568 (inch). Do not mix them; grooves are designed specifically for one or the other. **Q: What storage rules apply to elastomer O-rings?** Cool, dark, dry, in sealed original packaging; away from ozone/UV and solvent vapors. Apply FIFO, keep batch labels/CoC, and follow the supplier’s shelf life. **Q: Can I cut an O-ring from cord and bond it (spliced) for a mechanical seal?** Don’t do this in this application. For mechanical seals, you want molded, endless rings; bonded splices are weak points, especially under pressure and temperature fluctuations. **Q: Which installation tips prevent twisting, nibbling, and premature wear?** Do not twist or roll over the shaft; use installation sleeves/cones, burr-free grooves, and a chemically compatible assembly lubricant. Work cleanly, apply even pressure, and after assembly check for free, stress-free seating. ### [O-rings for coffee machines](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-household-appliances/o-rings-for-coffee-machines/) **Q: What are the symptoms of worn O-rings in a coffee machine?** The most common symptoms are: water leaking under the machine, loss of brewing pressure, wet coffee pads, deteriorating coffee taste, and moisture around hose connections. **Q: Can I replace an O-ring myself?** Yes, usually. With the right size, a suitable replacement ring, and some food-grade silicone grease, this can be done easily at home. **Q: How often should I replace O-rings in an automatic coffee machine?** Replace O-rings every 1 to 2 years for home use. For office or intensive use, inspect every 6 to 12 months. The brew group O-rings wear fastest due to constant mechanical stress. **Q: Which certifications are important?** At a minimum, EC 1935/2004 for Europe or FDA 21 CFR 177.2600 for the US. For drinking-water contact, NSF, WRAS, or KTW are relevant additions. ### [O-rings in watches](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-household-appliances/o-rings-in-watches/) **Q: What is an O-ring and where is it placed in a watch?** An O-ring is a circular rubber ring used to seal the gaps between components of, for example, a watch. You usually find them around the crown, the case back, or beneath the crystal. **Q: Which types of O-rings are most commonly used in watches?** The most commonly used O-rings in watches are NBR (nitrile rubber) and EPDM. NBR O-rings resist oil and wear, whereas EPDM O-rings offer better resistance to UV radiation, ozone, and water. The choice depends on the type of watch and the intended use. **Q: How can I tell the O-rings in my watch need replacing?** O-rings in watches lose their elasticity over time and can crack or deform. Symptoms include reduced water resistance, condensation under the crystal, or visible wear on inspection. Regular maintenance prevents the movement from being damaged due to a damaged O-ring. **Q: How often should watch O-rings be inspected or replaced?** It’s recommended to check O-rings during every service or battery replacement. With daily use or exposure to water or sunlight, replacement may be needed every 3–5 years, depending on the material. **Q: Where can I buy the right O-rings for watches?** You can buy the right O-rings for watches from us. In our webshop you’ll find a wide range of NBR and EPDM O-rings, specifically suitable for watches and other precision applications. ### [O-rings for valves: guide to water and wastewater treatment](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-drinking-water-and-waste-treatment/o-rings-for-valves-guide-to-water-and-wastewater-treatment/) **Q: Which O-ring is (standard) suitable for drinking water?** EPDM is generally the first choice. Make sure you select a drinking-water grade with WRAS or NSF 61 certification, and that the valve O-rings also match your groove in terms of hardness and compression set. For critical points under WRAS/BS 6920, WRAS-certified O-rings are often required. **Q: When should I use PTFE back-up rings?** If you work with higher pressure, have a larger gap, or expect pressure spikes/water hammer. PTFE back-ups limit extrusion and extend service life. For many butterfly and gate valves in networks, this is a sensible standard, especially for Butterfly Valve O-rings and Gate Valve O-rings that face pre... **Q: Is FKM better than EPDM for chlorine?** Not necessarily. FKM performs well with oils/fuels but is less suitable for hot water/steam and some oxidizers. For chlorine or chloramine dosing, a suitable EPDM grade or, under severe conditions, an inert solution (e.g., PTFE insert or FFKM) is often better. In dosing lines with higher oxidative l... **Q: How do O-rings affect the operating torque of my valve?** The stem seal contributes to friction. Choose a suitable compound, size the groove according to ISO 3601, and use a drinking-water-approved lubricant to prevent stick-slip and keep the torque stable. This keeps valve O-rings in top condition, even with frequent actuations. **Q: How often should I replace O-rings in valves?** That depends on switching frequency, medium, and temperature. In critical lines (disinfection, inlet), a preventive replacement during scheduled shutdowns is advisable. Inspect for compression set, cracks, and signs of extrusion; replace if in doubt. O-rings for valves are inexpensive compared to th... **Q: What documentation should I keep for audits?** Keep batch and compound codes, certificates (WRAS/KIWA/NSF 61), any test reports, and a note of groove dimensions and tightening torques. This allows you to demonstrate that O-rings for valves meet the requirements, perform reproducibly, and that the O-rings for valves are traceable. ### [O-ring flange seal in the chemical industry](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-the-chemical-industry/o-ring-flange-seal-in-the-chemical-industry/) **Q: Which materials should I choose for solvents or strong acids?** Start with FKM and assess the fluid specifications; for the most severe media, FFKM is often the safest choice. For fully static flanges, PTFE can be a solution, provided you design the groove for it so that the O-ring flange seal retains its shape. **Q: Which standards are relevant?** ISO 3601 and AS568 govern dimensions and tolerances; NORSOK M-710 focuses on performance in oil and gas environments, including explosive decompression. Following these references accelerates procurement and audit processes. **Q: Can I standardize one type of ring across all my lines?** Standardization helps, but always match the medium, temperature, and pressure. Set up a short decision tree and establish materials and codes for each line, so that the O-ring flange seal is demonstrably suitable everywhere. ### [O-ring for hydraulic cylinders in arm and bucket cylinders](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-construction-installation-technology/o-ring-for-hydraulic-cylinders-in-arm-and-bucket-cylinders/) **Q: When do I choose NBR, HNBR, FKM or PU?** Standard HLP oil and normal temperatures: NBR. Warmer oil/chemically more aggressive additives: FKM. More heat and ozone, but FKM not needed: HNBR. Heavy dynamics with wear focus: PU (provided it is compatible with the medium). **Q: Do I always need a PTFE back-up ring?** Not always. With high differential pressure, pressure spikes, or larger clearances, a PTFE back-up ring is advisable to prevent extrusion. Combine with correct groove dimensions (ISO 3601). **Q: What does the wiper/scraper do with respect to the rod seal?** The wiper keeps dirt, water, and mud out. The rod seal maintains pressure integrity. Together with a guide ring, the rod stays centered and the seal protected. **Q: How do I recognize compression set in the field?** Flattened cross-section, glossy/hardened rubber, and a bucket that slowly sinks. Replace the ring and check temperature, medium, and groove compression. **Q: What is a safe final guideline for procurement/maintenance?** Whoever wants to prevent downtime starts with an O-ring for hydraulic cylinders that matches the medium, temperature, and load. ### [O-ring for slurry pumps](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-agriculture-horticulture/o-ring-for-slurry-pumps/) **Q: When do I choose EPDM, NBR or FKM?** EPDM excels in aqueous media and outdoor installation, NBR in mechanical wear resistance, FKM in chemical and thermal resistance. Look at medium, temperature and weather exposure. If in doubt, start with an EPDM O-ring for slurry pumps and evaluate after the season for wear pattern and any chemical ... **Q: What is the best hardness?** 70 Shore A is the practical standard for static seals; choose harder at higher pressure, larger clearances or strong abrasion. In dynamic applications, a slightly softer ring can actually seal better at low pressure, but watch for increased wear. **Q: Does lubrication really help?** Yes. A thin, compatible film limits torsion and prevents cutting. Do not use mineral oil with EPDM. With repeated disassembly during the season, a minimal moistening before assembly may already be sufficient. **Q: Should I reuse old rings?** No. Due to compression set and microcracks they seal worse. New rings prevent failures. Recycle old elastomers if possible via the workshop’s waste stream. **Q: What standard is relevant?** ISO 3601 for sizes/tolerances and, where applicable, EN 681-1 for water/wastewater seals. When replacing, follow the size from the parts book. Manufacturer codes or batch labels help to reinstall exactly the same quality. ### [O-ring for infusion pumps: applications, materials and standards](https://www.o-ring-stocks.eu/our-services/industry/o-rings-for-medical-and-pharmaceutical-industry/o-ring-for-infusion-pumps-applications-materials-and-standards/) **Q: Are there O-rings in the infusion tubing or the Luer connection?** Not in standard IV sets: they rely on welded/clamped parts and the Luer cone. The O-rings are in the pump unit for environmental and mechanical sealing, not in the patient fluid path. **Q: Which materials are the most common?** For an O-ring for infusion pumps, silicone is popular for its elasticity and inertia; EPDM excels with water/ozone and many cleaning cycles; FKM performs well under heat and chemical load; and an FEP-encapsulated O-ring combines chemical resistance with resilience. Request USP Class VI where needed ... **Q: How do I recognize a ring that’s "worn out"?** Watch for loss of resilience, cracks, glossy spots from friction, surface erosion, or a noticeably flattened cross-section. These are classic replacement triggers. **Q: Should you lubricate during assembly?** Only if allowed by the supplier and with a lubricant compatible with your compound and application. Over-application can trap dirt or affect measurements. **Q: What is a safe baseline approach for selection?** Define the function and environment per position, choose the material profile (Silicone, EPDM, FKM or FEP-encapsulated), request USP Class VI where relevant, define hardness and dimensions, and validate the set-up in your own cleaning and service protocol. ### [O-ring for ballast water treatment: design, materials and practice](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-maritime-shipbuilding/o-ring-for-ballast-water-treatment-design-materials-and-practice/) **Q: Which size series should I choose for an O-ring for ballast water treatment in mixed metric–inch installations?** Choose one leading standard for the O-ring for ballast water treatment and make adapter parts where needed. ISO 3601 provides clear tolerances and offers metric series that match well with European components. **Q: How do I make the sealing seawater-resistant without overkill in material selection?** Base your choice on medium, temperature, and cleaning. Aim for seawater-resistant behavior via water-oriented compounds and secure your mechanics with the right squeeze and good groove finish. **Q: When is it worth combining an O-ring for ballast water treatment with a back-up ring?** At higher pressure, pulsations, or larger gaps. A PTFE back-up prevents extrusion of the O-ring for ballast water treatment. **Q: Which materials are suitable when oil and water alternate?** Choose oil-resistant options. FKM/Viton® is a strong all-rounder. In warmer, chemically harsher zones, AFLAS® can help. For critical positions, FFKM offers maximum margin. **Q: Is EPDM always the best choice near the reactor?** Not always. EPDM is strong in water and oxidants, but always compare the temperature profile, chemistry, and mechanics with the design of the O-ring for ballast water treatment. **Q: What role does pump selection play in my sealing strategy?** Vibrations, pressure fluctuations, and assembly quality around the ballast pump affect the required squeeze and hardness. Adjust the design and material of the O-ring for ballast water treatment accordingly. ### [O-rings in heat exchangers: reliable sealing for power plants](https://www.o-ring-stocks.eu/our-services/industry/o-rings-for-power-energy-industry/o-rings-in-heat-exchangers-reliable-sealing-for-power-plants/) **Q: Why are O-rings in heat exchangers so important?** They prevent leakage between different process streams and ensure energy efficiency and safety. **Q: Which material is most suitable for hot water and steam?** EPDM is the most suitable, due to its excellent resistance to water, steam and oxidation. Especially in installations with hot water and steam, O-rings in heat exchangers made from EPDM compound retain their elasticity and leak-tightness even after thousands of operating hours. **Q: When do you choose FKM (Viton®) or FFKM?** FKM (Viton®) is used at high temperatures and with oils; FFKM for extreme chemical exposure or very high temperatures. In practice, O-rings in heat exchangers with FKM compound are often used in oil circuits, while FFKM is preferred in chemically aggressive installations where maximum resistance is ... **Q: What exactly does a PTFE back-up ring do?** It prevents the O-ring from being forced into the gap under high pressure or temperature, preventing leakage. **Q: Which standard applies to the dimensions and tolerances of O-rings?** The international standard ISO 3601 defines dimensions, tolerances and quality levels. **Q: How often should O-rings in heat exchangers be replaced?** That depends on the medium, temperature and cycles. In many installations they are replaced at every planned maintenance shutdown to avoid downtime. In continuously operating plants, such as baseload power stations, O-rings in heat exchangers are often replaced annually to prevent unexpected outages... ### [O-rings in pharmaceutical centrifuges: reliable sealing for pharmaceutical processes](https://www.o-ring-stocks.eu/our-services/industry/o-rings-for-medical-and-pharmaceutical-industry/o-rings-in-pharmaceutical-centrifuges-reliable-sealing-for-pharmaceutical-processes/) **Q: Which material is most suitable for steam sterilization?** A pharmaceutical EPDM O-ring offers the best resistance to prolonged steam and high temperature. As a result, the seal in O-rings in pharmaceutical centrifuges remains reliable, even with repeated sterilization. **Q: How can I recognize wear or compression set?** When an O-ring shows flat contact surfaces or does not spring back, this indicates an increased compression set O-ring and it should be replaced. **Q: Why are FDA 21 CFR 177.2600 and USP Class VI important?** These certifications demonstrate that O-rings in pharmaceutical centrifuges do not release substances that could affect product quality. **Q: How often should O-rings be replaced?** Depending on the number of CIP/SIP cycles and chemical exposure, usually after 6 to 12 months, or earlier if visual damage is observed. **Q: Are coloured O-rings allowed?** Yes, provided the pigments are fully FDA- and USP Class VI–approved and support visual inspection. **Q: What are common installation errors?** Sharp groove edges, excessive squeeze, and incorrect size per DIN 3771 O-ring sizes are among the most common errors with O-rings in pharmaceutical centrifuges. ### [O-rings in pumps for corrosive media](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-drinking-water-and-waste-treatment/o-rings-in-pumps-for-corrosive-media/) **Q: Which materials are suitable for O-rings in pumps for corrosive media?** EPDM, FKM (Viton®) and Silicone are the most commonly used materials due to their chemical resistance and temperature range. **Q: How can I identify wear on O-rings in pumps for corrosive media?** Watch for deformation, sticky residues, or micro-cracks. These signs indicate ageing or incompatibility with the medium. **Q: Are O-rings in pumps for corrosive media suitable for drinking water?** Yes, provided they comply with standards such as WRAS or KTW. EPDM is generally the best choice for this. **Q: What is the advantage of an O-ring according to ISO 3601?** This standard ensures consistent dimensions, reducing leakage and assembly damage. **Q: How often should O-rings in pumps for corrosive media be replaced?** That depends on the medium, temperature and pressure, but preventive replacement after 12 to 18 months is common. **Q: Why do some O-rings in pumps for corrosive media fail prematurely?** More often due to incorrect material selection or excessive compression than due to manufacturing defects; compatibility is crucial. ### [O-rings in the dredging industry](https://www.o-ring-stocks.eu/our-services/industry/o-rings-in-maritime-shipbuilding/o-rings-in-the-dredging-industry/) **Q: Why do O-rings in the dredging industry wear out faster than in other sectors?** The combination of sand, water and pressure makes the environment extremely demanding. These factors cause erosion and deformation, which makes regular inspection important. **Q: Which material works best in pure seawater?** EPDM is ideal for outdoor applications because it offers excellent resistance to salt, UV and ozone. **Q: When should I use HNBR instead of NBR?** HNBR is used when pressure and temperature are higher or when a longer service life is required. **Q: Is FKM always the best choice for pump seals?** FKM offers broad compatibility, but for pure water EPDM is often more effective. **Q: Why do pipeline seals sometimes fail prematurely?** This is often due to an incorrect material selection or insufficient groove support, which leads to extrusion. **Q: How can I extend the service life of hydraulic seals?** Through regular inspection, correct lubrication and timely replacement, the seal remains stable and safe. ### [Colored O-rings](https://www.o-ring-stocks.eu/knowledge-base/colored-o-rings/) **Q: What do the colors of O-rings indicate?** The color of an O-ring is often a useful visual indication, but not a fixed guarantee of the material. Some colors occur more frequently with certain compounds, but checking the material always remains important. **Q: Is the color of an O-ring an indication of the material?** Yes, often as an initial indication. Certain colors are regularly associated with materials such as NBR, EPDM, VMQ silicone, or FKM / Viton®, but this may vary by manufacturer or compound. **Q: Which O-ring color is often associated with Viton® / FKM?** FKM / Viton® is often supplied in brown or green. However, other colors are also possible, which is why you should never select an O-ring based on color alone. **Q: Are O-ring colors a fixed standard?** No, in practice O-ring colors are not a universal standard. Colors are often used for identification and coding, but they may vary by supplier and application. **Q: Can O-rings also be made in a specific RAL color?** Yes, in many cases O-rings can also be produced in a desired or popular RAL color. This is useful for internal coding, product differentiation, or a specific visual appearance. ### [O-ring Groove - Static](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-static/) **Q: What is the difference between static and dynamic sealing?** In static sealing, the components no longer move relative to each other after assembly. In dynamic sealing, there is relative movement, such as with a piston or rod. The compression percentages are higher in static sealing than in dynamic sealing, because there is no wear caused by movement. **Q: Which static groove type should I choose?** For cylindrical connections: radial compression. For flat connections (lids, flanges): axial compression. If the ring must not fall out during assembly: trapezoidal groove. If a rectangular groove does not fit the design: triangular groove. For vacuum applications: a vacuum-specific groove with adju... **Q: Why is my static seal leaking while the O-ring looks fine?** The three most common causes are: the groove has been milled too deep (too little compression), the sealing surface is too rough (leak path along the ring), or the gap between the components is too large (extrusion at higher pressures). Check the groove depth with a depth gauge and the surface quali... **Q: How do I determine the correct compression for my application?** Use the formula: compression (%) = (d2 − t) / d2 × 100. The recommended range for static radial compression is 15 to 30%. For axial compression: 1 to 3% compression (internal pressure) or max. 6% expansion (external pressure). Use the O-ring calculation tool for your specific combination. **Q: Do I need to add a chamfer for all static applications?** Yes, for all groove types in which the O-ring is pushed over an edge during assembly. That applies to radial compression. In axial compression, the ring is placed in a flat groove and a chamfer is not required. The same applies to the trapezoidal groove and the triangular groove as to axial compress... **Q: Which material is the most universal for static O-rings?** NBR covers most applications: mineral oils, water and greases at temperatures up to +100 °C. For applications in which NBR falls short, FKM is the next step because of its broad chemical resistance and higher temperature tolerance. **Q: When are back-up rings required?** Back-up rings are required when the gap between the components is too large at the operating pressure for the given hardness of the ring. As a rule of thumb: above 100 bar in static applications, back-up rings are recommended regardless of hardness. Consult the gap width table for the exact limits p... ### [O-ring Groove - Static - Radial Compression](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-static/o-ring-groove-static-radial-compression/) **Q: What is the recommended compression for static radial sealing?** 15 to 30% of the cross-section diameter. Formula: (d2 - t) / d2 × 100. The dimensions in the standard table always fall within this range. **Q: What happens if I omit the chamfer?** During assembly, the ring develops microscopic internal cracks. These only become visible under pressure, sometimes only after hours or days. A chamfer of 15–20 degrees prevents this. **Q: Are the groove dimensions different for silicone O-rings?** The groove geometry is identical. Only the maximum gap width must be halved, because silicone has a lower tensile strength and extrudes more quickly. **Q: Which material should I choose?** NBR for oil and water, EPDM for steam and outdoor applications, FKM for chemicals up to +200 °C. Consult the chemical resistance guide for your specific medium. ### [O-ring Groove - Static - Axial Compression](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-static/o-ring-groove-static-axial-compression/) **Q: What is the difference between axial and radial compression?** In radial compression, the ring is compressed between two cylindrical surfaces, perpendicular to the axis. In axial compression, the ring is compressed between two flat mating surfaces, in the direction of the axis. Axial compression is used for lids, flanges and flat connections. **Q: How much compression is permitted in axial compression?** With internal overpressure: approximately 1% up to a maximum of 3%. With external pressure, the ring may expand slightly, up to a maximum of 6%. Outside these limits, fatigue or permanent deformation occurs. **Q: Do I also need a chamfer for axial compression?** No. In axial assembly, the O-ring is placed in a flat groove, not slid over an edge. Chamfers are therefore not required and are not included in the size table for axial compression. **Q: Can I use the same O-ring for radial and axial applications?** Yes, the ring itself is the same. Only the groove differs. The groove depth, groove width and radii are dimensioned differently for axial applications than for radial ones. Always use the table that belongs to the installation type. **Q: Which material is best for axial seals under high pressure?** For high pressures and aggressive media, FKM (Viton) is the preferred choice because of its high chemical resistance and mechanical stability. For standard applications, NBR is sufficient. Consult the chemical resistance guide for your specific medium. ### [O-ring Groove - Static - Vacuum](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-static/o-ring-groove-static-vacuum/) **Q: Why is the tolerance on groove depth negative in vacuum applications?** A shallower groove gives a higher radial compression and ensures that the ring fills the groove more densely. Less free volume means a longer diffusion path for gas molecules through the rubber, which reduces the leak rate. **Q: Can I use a standard O-ring for vacuum sealing?** Yes, the ring itself is the same. Only the groove and the surface are different. Do use the right material choice: FKM has the lowest gas permeability and is therefore the preferred option for higher vacuum requirements. **Q: How low can I go with an O-ring as a vacuum seal?** With a properly designed vacuum groove, an FKM O-ring, vacuum grease and double rings, a leak rate of 10-8 mbar·l/s is achievable. For higher requirements (10-10 and lower), metal or PTFE seals are required. **Q: Why is FKM recommended for vacuum?** FKM has lower gas permeability than NBR or EPDM, which means less gas diffuses through the material itself. In addition, FKM is resistant to most cleaning chemicals used in vacuum systems and has low outgassing at low pressures. **Q: Does vacuum grease really help?** Yes. Vacuum grease reduces surface microporosity and improves the contact between the ring and the sealing surface. It also lowers assembly friction and protects the ring during assembly. Only use grease that is compatible with the rubber and with the vacuum process. ### [O-ring Groove - Static - Triangular Groove](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-static/o-ring-groove-static-triangular-groove/) **Q: When should I use a triangular groove?** Only if a rectangular groove is not structurally feasible, for example because of insufficient material depth or in an existing part where milling would create a structural objection. In all other cases, the rectangular groove is the better choice. **Q: Is the sealing performance with a triangular groove as good as with a rectangular groove?** When executed correctly, the sealing performance is comparable. But the triangular groove has less tolerance for dimensional deviations and places higher demands on machining accuracy. The risk of errors is greater. **Q: Can I use a triangular groove for every cross-section diameter?** The standard table runs from d2 = 1.50 mm to d2 = 15.00 mm. Outside that range, no standardized dimensions are available. **Q: What is the difference between the tolerance for the triangular groove and for the rectangular groove?** For the rectangular groove, the tolerance on groove width b1 is a fixed +0.25 mm. For the triangular groove, the tolerance varies per cross-section diameter, from +0.1 mm for small sizes up to +0.4 mm for large sizes. Always consult the size table for the specific size. ### [O-ring Groove - Static - Trapezoidal Groove](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-static/o-ring-groove-static-trapezoidal-groove/) **Q: When do I use a trapezoidal groove instead of a rectangular groove?** Only if the ring must remain in place during or after assembly without the parts already being closed. Think of overhead assemblies, regularly opening connections or situations where the ring is positioned before assembly and transport follows afterwards. **Q: Is the sealing performance of a trapezoidal groove better than that of a rectangular groove?** No. The sealing performance is comparable at the same compression. The advantage of the trapezoidal groove lies entirely in its retention function: the ring can no longer fall out. **Q: Why are the tolerances tighter for the trapezoidal groove?** Because the clamping action depends on the exact dimensional relationship between the ring diameter and the groove geometry. A larger dimensional deviation reduces the clamping action if it is too wide, or makes insertion impossible if it is too narrow. **Q: Can I use a hard O-ring (90 Shore A) in a trapezoidal groove?** That is not recommended. Hard rings are less elastic and are more difficult to press into the trapezoidal groove. The clamping action is also less strong at higher hardness levels. 70 Shore A is the recommended hardness for trapezoidal grooves. ### [O-ring Groove - Dynamic](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-dynamic/) **Q: What is the difference between dynamic hydraulics and pneumatics for O-rings?** The groove geometry is similar, but the compression in pneumatics is slightly lower (7 to 13% versus 9 to 16% in hydraulics). The biggest practical difference is lubrication: hydraulic fluid lubricates the ring with every stroke. Air does not. In pneumatics, deliberate lubrication is therefore stron... **Q: How do I prevent twisting in dynamic O-rings?** Keep the groove width b1 strictly within the specified tolerances. A groove that is too wide gives the ring room to roll. Also avoid extremely low compression at high stroke frequencies. When replacing the ring, always check the groove width again: wear of the groove increases b1 and raises the risk... **Q: How strict is the roughness requirement for dynamic sealing?** The sealing surface must be Ra max. 0.4 µm (Rz max. 1.2 µm). That is four times stricter than in static applications. A rougher surface wears the ring with every stroke, especially in pneumatics without lubrication. **Q: When do I need back-up rings in dynamic applications?** In dynamic use, the limits are lower than in static use. Above 63 bar at 70 Shore A, back-up rings are recommended. Back-up rings are always installed on the low-pressure side of the groove. With pulsating pressure, back-up rings on both sides are desirable. **Q: Can I also use a static O-ring dynamically?** The ring itself is the same, but the groove is not. Static grooves have a deeper t (higher compression) than dynamic grooves for the same cross-section diameter. Using a static groove for dynamic applications causes too much friction and accelerated wear. Always use the groove that belongs to the in... **Q: Which material has the best wear resistance in dynamic use?** NBR has good wear resistance for most hydraulic media. FKM is slightly less wear-resistant than NBR but offers better chemical resistance. In pneumatics without lubrication, EPDM has better dry-running characteristics than NBR. PTFE-coated rings have the lowest friction but are more vulnerable to da... **Q: How long does a dynamic O-ring last?** That depends on the pressure, the stroke speed, the medium, the lubrication and the surface quality of the sealing surface. Under favourable conditions, hundreds of thousands of strokes are achievable. At higher speeds, with insufficient lubrication or with a sealing surface that is too rough, the r... ### [O-ring Groove - Dynamic - Pneumatics](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-dynamic/o-ring-groove-dynamic-pneumatics/) **Q: Why is the compression lower in pneumatics than in hydraulics?** Air does not lubricate, which means that higher contact pressure immediately causes higher friction. To maintain the stroke and positioning accuracy of the cylinder, the compression is deliberately kept low. This does, however, require a tighter sealing surface. **Q: Do I need lubrication for pneumatic O-rings?** Not mandatory, but strongly recommended. Silicone grease or an oil mist reduces friction, extends service life and lowers the risk of twisting. Use grease that is compatible with the rubber and with the medium. **Q: Can I use the same O-ring for hydraulics and pneumatics?** The ring itself can be the same, but the groove is dimensioned differently. The groove depth t is greater in pneumatics (lower compression) than in hydraulics for the same cross-section diameter. Always use the table that belongs to the installation type. **Q: What is the maximum operating pressure for O-rings in pneumatic applications?** With a gap of 0.15 mm and 80 Shore A, the maximum pressure in dynamic use is approximately 30 to 63 bar. Most pneumatic systems operate at 6 to 16 bar, which is well within that range. **Q: Which material is best for pneumatic O-rings without lubrication?** EPDM or FKM tolerate dry running better than NBR, which can harden or crack during prolonged dry running. Silicone is wear-resistant but less strong. For dry-running pneumatics, also consider special PTFE-coated or filled rings. ### [O-ring Groove - Design - Groove Design](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-design/o-ring-groove-design-groove-design/) **Q: Does an O-ring groove always have to be rectangular?** That is the standard and the recommendation for virtually all applications. Other groove shapes (trapezoidal, triangular) are only useful if the design rules out a rectangular groove or if the specific retention function of the trapezoidal groove is required. **Q: How many degrees may groove sidewalls be tapered?** A maximum of 5 degrees relative to perpendicular. More than 5 degrees changes the effective groove width as a function of depth, which leads to uneven support of the ring and a higher risk of leakage. **Q: Why are corner radii needed in the groove?** Sharp corners in the groove concentrate stress in the rubber on a small area. At higher pressures or under pulsating loads, this initiates cracking that starts in the corner and spreads further. The standard radii r1 and r2 distribute that stress over a larger contact area. **Q: How do I check whether my groove complies with the standards?** Measure the groove depth t with a depth gauge and the groove width b1 with a caliper or gauge pin. The sidewall angle can be measured with a profile measuring instrument or by means of a cross-section of a test piece. Also visually inspect all transitions for burrs. **Q: Do I need to inspect the groove again after multiple installations?** Yes, especially in dynamic applications. Mechanical wear, corrosion or cavitation can make the groove wider. A groove that is too wide creates room for twisting and extrusion, even if the ring itself is still intact. Periodic inspection of the groove width is part of proper maintenance. ### [O-ring Groove - Design - Surface](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-design/o-ring-groove-design-surface/) **Q: Why is the roughness requirement for dynamic sealing much stricter than for static sealing?** With every stroke, the O-ring slides over the sealing surface. A rough surface mechanically wears the ring, a little more with every movement. In static applications, this does not occur: the ring remains stationary on the surface and can bridge small roughness peaks through elastic deformation. **Q: What is the difference between Ra, Rz and Rmax?** Ra is the average deviation of the roughness profile from the mean line: an average value over the entire measuring length. Rz is the average height of the five highest peaks minus the five deepest valleys: it is more sensitive to outliers. Rmax is the largest measured peak in the profile. For seals... **Q: My Ra value is fine, but it still leaks. What could be wrong?** The most common cause is that Rmax or Rz exceeds the standard, even if Ra is within the specified values. One or a few deep scratches or machining marks can create a leakage path without noticeably affecting the average roughness. Also measure Rz and Rmax, and visually inspect the surface for scratc... **Q: How do I deal with a sealing surface that is slightly damaged?** In static applications, light scratches can sometimes be ground out or polished, provided the dimensional accuracy still meets the requirements afterwards. In dynamic applications, reworking is almost always necessary because the requirement is stricter. After reworking, always check the dimensions ... **Q: Does Ra 0.4 µm also apply to the groove bottom in dynamic use?** No. In dynamic use, the groove bottom may have a maximum Ra of 1.6 µm, which is four times less strict than the sealing surface. The groove bottom is not in contact with the moving counterface and does not directly contribute to wear of the ring during the stroke. ### [O-ring Groove - Design - Chamfer](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-design/o-ring-groove-design-chamfer/) **Q: Why is the chamfer angle 15 to 20 degrees and not steeper?** An angle smaller than 15 degrees provides insufficient guidance. An angle greater than 20 degrees provides too little axial length for the chamfer when installation space is limited and can affect the wall. The 15 to 20 degree range is the optimum between guidance effect and design feasibility. **Q: Do I also need a chamfer on the exit side in dynamic seals?** Yes, especially in applications where the ring is removed during overhaul. Without a chamfer on the exit side, the ring is damaged during removal. That causes problems if the ring is reused, and it also gives a distorted picture of the condition of the seal. **Q: Do I also need to make a chamfer for axial squeeze?** No. In axial squeeze, the ring is placed in a flat groove and does not pass a sharp edge. Chamfers are not needed in axial applications and are not included in the dimension table for axial squeeze. **Q: How do I prevent damage during installation over a thread?** Use an installation sleeve or installation mandrel: a smooth, slightly conical auxiliary tool that fits over the thread and temporarily covers the sharp flanks. The ring is slid over the sleeve into position, after which the sleeve is removed. This is standard installation practice for rod seals wit... **Q: Can I also apply the chamfer after machining if I forgot it?** Yes, the chamfer can be added afterwards with a cutting tool, a file or a small milling cutter, depending on the material and accessibility. Make sure the transition is finished burr-free afterwards. After reworking, check whether the ring slides freely over the chamfer without resistance. ### [O-ring Groove - Design - Gap Size](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-design/o-ring-groove-design-gap-size/) **Q: What is gap extrusion and how can I recognize it?** Gap extrusion occurs when the operating pressure forces the rubber of the O-ring into the gap between the components. It can be recognized by so-called nibbling damage: frayed or broken-off pieces of rubber on the low-pressure side of the ring. In static applications, the damage is sometimes only vi... **Q: When should I choose a harder O-ring because of the gap?** If the gap cannot be made smaller for design reasons and the operating pressure exceeds the maximum gap value for 70 Shore A. A ring of 80 or 90 Shore A tolerates a larger gap at the same pressure. The compromise is that a harder ring requires a smoother sealing surface at low pressures. **Q: How many back-up rings do I need?** With pressure from one side, one back-up ring on the low-pressure side is sufficient. With pressure from both sides or with pulsating pressure, back-up rings on both sides of the O-ring are recommended. **Q: Why do I need to halve the gap values for silicone materials?** Silicone has a lower tensile strength than NBR or FKM. At the same pressure and gap, silicone extrudes earlier because the rubber is more easily pushed through the opening. The corrected values are half of the values in the table. **Q: Which back-up ring matches which O-ring?** PTFE back-up rings are the most universal choice: low friction, broad chemical resistance and high temperature limits. PE back-up rings are more economical and suitable for less demanding applications. NBR concave back-up rings are used in applications where slight resilience is desired. View the fu... **Q: How do I calculate the one-sided gap in my fit?** The one-sided gap is: (bore inner diameter minus rod outer diameter) divided by 2. Use the worst-case values from the tolerance range: maximum bore and minimum rod. That combination gives the largest possible gap, and that value is the limit you compare with the table. ### [O-ring Groove - Design](https://www.o-ring-stocks.eu/knowledge-base/o-ring-groove-dimensions/o-ring-groove-design/) **Q: What is the most common cause of leakage in a correctly dimensioned O-ring?** In our experience, the sealing surface is the most underestimated factor. A groove geometry that is correct, a properly selected ring, and still leakage: in most cases there is a scratch, a turning groove or a machining mark on the sealing surface that forms a continuous leak path. Always inspect th... **Q: Do I need to check all four points during every assembly?** For a new groove: yes, all eight checkpoints. For overhaul or replacement of the ring in an existing groove: at minimum the groove width (wear), the sealing surface (damage) and the chamfer (burr formation due to wear of the edge area). Under normal use, the groove depth and radii generally do not c... **Q: Which error has the greatest impact on the service life of the seal?** In static applications, a missing or poor chamfer is the most decisive error for immediate service life: the ring starts its service already damaged. In dynamic applications, the surface quality of the sealing surface is the most decisive factor for the long term: a rough surface wears the ring with... **Q: When should I consider back-up rings?** Back-up rings are needed when the gap between the components is too large at the working pressure for the given hardness of the ring. Above 100 bar in static applications and above 63 bar in dynamic applications, back-up rings are recommended for most hardnesses. With pulsating pressure, back-up rin... **Q: How do I know whether my groove flanks are too steep?** During visual inspection, an angle of 5 degrees or less is not visible. Use a profile measuring instrument or measure the groove width at two depths: at the opening and at the bottom. If the bottom is narrower than the opening, the flanks are conical. The difference in width divided by the groove de... **Q: Is the surface finish of the groove base as critical as that of the sealing surface?** No. In static applications, the groove base may be Ra max. 3.2 µm, which is twice as rough as the sealing surface (Ra 1.6 µm). The groove base is not in contact with the medium and does not directly contribute to the sealing function. In dynamic applications, the groove base is Ra max. 1.6 µm, equal... **Q: What do I do if the gap in my design is too large?** There are three options: choose a harder O-ring (a higher Shore A tolerates a larger gap), modify the design to reduce the gap, or use back-up rings on the low-pressure side. Back-up rings are the most practical solution in existing designs. View the full range at o-ring-stocks.eu/back-up-rings/. > Multilingual AI content guide ## Language versions: - [nl] https://www.o-ring-stocks.eu/nl/llms.txt - [de] https://www.o-ring-stocks.eu/de/llms.txt - [fr] https://www.o-ring-stocks.eu/fr/llms.txt - [it] https://www.o-ring-stocks.eu/it/llms.txt - [es] https://www.o-ring-stocks.eu/es/llms.txt ## Technical files - [Sitemap index](https://www.o-ring-stocks.eu/sitemap-index.xml): XML sitemap with all key pages - [Sitemap](https://www.o-ring-stocks.eu/sitemap.xml): XML sitemap with all key pages - [robots.txt](https://www.o-ring-stocks.eu/robots.txt): Crawl and AI access instructions **Last update:** April 2026 **Contact for AI integration or data licensing:** info@o-ring-stocks.eu