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Frequently Asked O-ring Technical Questions
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Seal DesignParker provides recommendations for groove dimensions for all standard O-rings in a number of seal configurations. Parker's inPHorm for O-rings provides a great deal of assistance in seal material selection. Alternatively, we've developed a single page Seal Design Quick Reference. For safety's sake, we strongly encourage all customers to thoroughly test all seal designs before relying upon them. Parker cannot guarantee that any seal design will fully meet your specific needs.
Parker provides gland design recommendations. You may choose to alter these recommendations to better fit your needs. You may be able to modify our recommendations slightly and still obtain a reliable seal, but you'll want to test the design to ensure to your satisfaction that it meets your needs. There are a number of reasons for O-ring leakage. Try our on-line Troubleshooting to begin the process of seal failure analysis. Parker has compiled a series of tables of empirical data (in Microsoft Word format) that relate compressive load generated per inch of circumference to the O-ring's cross-section, hardness, and amount of squeeze. It is possible to estimate the running friction of an O-ring seal. Backup rings are used to improve the pressure resistance of a softer rubber seal to that of a 90 durometer seal material. Use our Extrusion Chart to determine if a backup ring is needed based on your seal hardness, gland clearance, and fluid pressure. Face seals are designed to achieve metal-to-metal contact between the faces, meaning a backup ring is not necessary. Use our Extrusion Chart to determine if the maximum recommended pressure of an O-ring seal based on your seal hardness and gland clearance. Unfortunately, there is no method available yet to accurately predict the application life of a rubber seal. Actual product performance testing remains the most useful method of determining a maximum time before replacement. In short, there is no one way to correctly install an O-ring. Any method of assembly should prevent installation damage to the O-ring. Surface lubrication, lead in chamfers, and the removal of all sharp edges are typically necessary in all O-ring assemblies. Parker Seal Group is one of the world's largest users of non-linear Finite Element Analysis. However, because of the amount of time and effort required, we must limit the use of this tool to the most demanding applications. Contact a Parker Applications Engineer for information about FEA work. The choice of a seal material is based on a number of factors, including the fluids in contact with the seal, the temperature, the pressure, any third-party requirements, and whether the seal is used statically or dynamically. Parker's inPHorm for O-rings provides a great deal of assistance in seal material selection.
Parker recommends using 6 times the cross-section of the seal (for example, 1.260" for an O-ring with 0.210" cross-section) for the radius to the inside edge of the groove. If space is limited, this can be reduced to three times the cross-section; a smaller radius is likely to cause buckling of the seal and installation difficulties. Some customers choose to reduce their machining costs by inserting O-rings into counter-bores rather than separately-machined face seal grooves. This design can be successful as long as a negative pressure situation caused by vacuum or high fluid flow velocity is avoided. (It is possible to suction an O-ring out of a counter-bore groove.) This design may also affect fluid flow dynamics, so validation testing is highly recommended. |
Seal Material TechnologyThe recommended shelf life of a rubber seal is determined by the base polymer. Click here for a letter that explains Parker's recommendations for rubber shelf life.Rubber O-rings are considered mechanical goods, and so do not require Material Safety Data Sheets per OSHA regulations. We recommend you first use inPHorm for material selection assistance. If your fluid(s) is / are not included in the material selection guide included in inPHorm, please contact an Applications Engineer for assistance. EPR is an abbreviation for Ethylene-propylene copolymer, while EPDM is an abbreviation for Ethylene-Propylene Terpolymer. We've written a brief letter that describes the differences between EPR and EPDM.Viton� is a registered trademark of DuPont Dow Elastomers for fluorocarbon elastomer. "A-type" fluorocarbon is considered "standard" fluorocarbon technology; this is the polymer used to make Parker compound V0747-75 and many others. Please see our Fluorocarbon Fact Sheet for a detailed description of the different types of fluorocarbon elastomers available. Please see our Fluorocarbon Fact Sheet for a detailed description of the different types of fluorocarbon elastomers available. Litharge (lead oxide) formerly was used to improve the acid resistance of a fluorocarbon compound. Since lead oxide is a potential environmental hazard, Parker O-Ring Division has eliminated its use. Instead, Parker compounds V0494-70 and V0894-70 achieve even better improvements in acid resistance through the use of acid-resistant B-type fluorocarbon polymer. Please see our Fluorocarbon Fact Sheet for more information. The method of curing or vulcanizing a rubber seal material is critical to the performance of the seal material in many cases. In nitrile rubber compounds, peroxide curing offers higher temperature stability and better compression set resistance. Parker compounds N0741-75, N0951-75, N0756-75, and N1210-90 are all peroxide cured. Peroxide-curing is not necessarily the best choice in cure systems in other materials; for example, in fluorocarbon compounds bisphenol provides much better compression set resistance than does peroxide curing. Platinum curing can theoretically be used to cure standard gum-stock silicone, but this phrase almost exclusively refers to Liquid Injection Molded (LIM) silicone. Parker O-Ring Division can supply LIM silicone O-Rings through the Global Business Unit. Parker O-Ring Division can supply LIM silicone O-Rings through the Global Business Unit. Kalrez� is a registered trademark of DuPont Dow Elastomers for perfluoroelastomer. Parker's Parofluor and Parofluor ULTRA compete in this marketplace. Chemraz� is registered trademark of Greene, Tweed for perfluoroelastomer. Parker's Parofluor and Parofluor ULTRA compete in this marketplace. Viton� is a DuPont Dow Elastomers trademark for fluorocarbon elastomer. To avoid trademark infringement, Parker refers to this type of material technology under the chemical description "fluorocarbon". Aflas� is a registered trademark of Asahi Glass Co. Ltd of Japan for their TFE/P elastomer. Parker compounds V1006-75 and V1041-85 are made from this type of technology. Again, Parker avoids trademark infringement by referring to this type of material as TFE/P. These terms are synonyms.HNBR (hydrogenated nitrile, also called HSN) is chemically similar to nitrile, except the carbon-carbon double bond found in nitrile is not present in HNBR, providing temperature stability up to 325 F and resistance to atmospheric ozone and weathering. Parker has evaluated a number of compounds for their specific vacuum weight loss (offgassing.) Keep in mind that these values are highly dependent upon the compound formula, so these values are for these specific Parker compounds. They should not be accepted as "industry standard" values for generic materials. Each of these is a method of testing the hardness of a rubber sample by pressing an indentor (called a frustrum) into a rubber sample and measuring the force and / or amount of penetration. Each of these methods uses a slightly different indentor, method of controlling the force, and / or method of measuring the penetration. As a result, each of these hardness measurement devices will generate a different number on the same sample, and there is no direct correlation from one "scale" to another.
In the US, Shore A is the most common method of measuring rubber hardess. Shore D is typically used for very hard rubber compounds and plastics (50 Shore D is approximately 90 Shore A). Shore M is specialized for use on O-rings. IRHD is a fully automated measuring procedure preferred in Europe. At Parker, we control each batch of rubber by measuring the Shore A hardness.
All of the test methods can provide repeatable results (all the numbers will be about the same for a given sample and test method), but the number provided by one method may be very different from that of another. For this reason, it is not valid to compare the hardness results obtained by one test method with the pass / fail limits written for another. |
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Parker Compounds Because Parker is constantly developing new materials, only the standard compounds are shown in the Parker O-ring Handbook and O-ring Reference Guide. For an updated compound offering list, refer to Parker's Compound Offering Manual. Specific information on a Parker compound can be found in the Compound Offering Manual and also in inPHorm. The selection of a seal material for any application must take into account the fluid, temperature, pressure, and gland design. Parker's inPHorm seal design software automates this task. Material Test Reports for Parker compounds can be viewed over the Internet or on Parker's inPHorm seal design software package. Contact Parker O-ring Division for the recommend replacement for any obsolete seal material. Parker has developed several compounds to maximize performance in unique applications. In many applications, a standard material may be acceptable, but a special material will offer improved performance. Very seldom are the differences between seal compounds visible. Differences in the base polymer, cure system, and amount and type of other compound ingredients play a significant role in both the seal performance and the seal cost. The phrase "you get what you pay for" usually applies in the O-ring industry. In most refrigerants, Parker's neoprene compounds C0873-70, C1276-70, C1277-75, and C1278-80 are the first choices in material. However, automotive R-134a applications typically require high temperature stability up to 300 degrees Fahrenheit. In these applications, HNBR compounds like Parker's N1173-70, N1239-70, and N1231-80 are frequently used.N70 is not a Parker compound number. This is probably a reference to generic 70 durometer nitrile rubber. We recommend Parker compound N0674-70 as a replacement / improvement. Absolutely not. The term "latex rubber" is commonly used (incorrectly) to refer specifically to natural rubber latex. Parker O-Rings do not contain any natural rubber latex, which is suspected of causing allergic reactions in some people. Absolutely not. Some seal materials exhibit a dusty gray or white coating on the outside surface of the seal material called bloom. Bloom is primarily composed of non-reacting catalysts used to speed the curing process. The presence of bloom seldom if ever affects seal performance in application.Internal lubricants are typically oils or waxes there are mixed into the raw material prior to molding. In application, this oil or wax migrates to the surface of the O-ring to provide lubrication and extend seal life. Internal lubricants can be extracted by exposure to hot oils or high heat. Internally lubricated compounds seldom if ever "run out" of internal lubricant solely through use. Parker offers a number of internally lubricated compounds. Nothing. Parker O-Ring Division has adapted its compound numbering system over the years, and all of these names refer to the same O-ring compound. We have written a letter explaining our compound numbering system in more detail.The Parker compound number for virgin (non-filled) PTFE O-rings is Z1415-95. Parker has evaluated a number of compounds for their specific vacuum weight loss (offgassing.) Keep in mind that these values are highly dependent upon the compound formula, so these values are for these specific Parker compounds. They should not be accepted as "industry standard" values for generic materials. Each of these is a method of testing the hardness of a rubber sample by pressing an indentor (called a frustrum) into a rubber sample and measuring the force and / or amount of penetration. Each of these methods uses a slightly different indentor, method of controlling the force, and / or method of measuring the penetration. As a result, each of these hardness measurement devices will generate a different number on the same sample, and there is no direct correlation from one "scale" to another.
In the US, Shore A is the most common method of measuring rubber hardess. Shore D is typically used for very hard rubber compounds and plastics (50 Shore D is approximately 90 Shore A). Shore M is specialized for use on O-rings. IRHD is a fully automated measuring procedure preferred in Europe. At Parker, we control each batch of rubber by measuring the Shore A hardness.
All of the test methods can provide repeatable results (all the numbers will be about the same for a given sample and test method), but the number provided by one method may be very different from that of another. For this reason, it is not valid to compare the hardness results obtained by one test method with the pass / fail limits written for another. |
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Specifications Parker offers a number of seal materials certified to the most common AMS and MIL material specifications. Parker supplies O-ring compounds to meet most standard ASTM D2000 / SAE J200 material specifications. Parker compound E1267-80 is certified to meet NAS 1613 Rev 4. |
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Colors Across the rubber industry, O-rings are not color coded. Many customers adopt a method of color-coding to help prevent mixed seal inventory. Seal materials cannot be conclusively identified by color. Fluorocarbon compounds are available from Parker in black, brown, and green. Across the rubber industry, O-rings are not color coded. Many customers adopt a method of color-coding to help prevent mixed seal inventory. Seal materials cannot be conclusively identified by color. In some cases, compounds of similar performance and different colors may be available, or we may be able to develop a custom material for your application. Refer to the Compound Offering for assistance, or contact a Parker Applications Engineer. Because of our ISO / QS controls, we cannot simply change the color of an existing seal material. Any colored dots applied to an O-ring are done so at customer request or to meet the requirements of a specification. For example, NAS 1613 Rev 4 requires all Class 1 material to have 1 white stripe and 1 white dot for identification.ChromAssure is a Parker recommended practice of color-coding O-rings at a customer location. Each base polymer is assigned a specific color to help distinguish it from another seal material. |
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Backup Rings Parbaks are hard rubber backup rings that are used to increase the pressure rating of a seal design. They're typically made from Parker compound N0300-90 or N1444-90, but can also be made for other materials as needed. Parker provides solid, spiral , and scarf cut PTFE backup brings for industrial applications. Parbak rubber backup brings can be stretched during installation and return to their original dimensions. In this regard, they are much easier to install than PTFE backup brings, and do not contain a scarf cut edge that may damage an O-ring seal. Back up rings are necessary when using a soft seal material in a high-pressure application. Backup rings provide no additional benefit when using a 90 durometer rubber O-ring material. Parker's Extrusion Chart provides information on the pressure rating of seal materials of various hardness. Parker can design and manufacture custom backup rings as needed. There are no standard backup rings for 5-x x x O-rings. Parker can design and manufacture custom backup rings for these O-rings as needed.Face seals are designed to achieve metal-to-metal contact between the faces, meaning a backup ring is not necessary. |
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Lubricants The recommended shelf life for Parker's O-ring lubricants O-Lube and Super-O-Lube is one year from the date of opening. Material Safety Data sheets for Parker's O-ring lubricants are available on-line. Parker provides usage recommendations for each of its lubricants. In some applications, it may be desirable to use alternate lubricants with O-rings. For example, vegetable oil or shortening may be used in FDA applications. In these cases, it is necessary to test to ensure complete compatibility with the seal material in question. Parker offers a number of internally lubricated compounds.Internal lubricants are typically oils or waxes there are mixed into the raw material prior to molding. In application, this oil or wax migrates to the surface of the O-ring to provide lubrication and extend seal life. Internal lubricants can be extracted by exposure to hot oils or high heat. Internally lubricated compounds seldom if ever "run out" of internal lubricant solely through use. For a small additional charge, Parker can provide a thin coating of dry PTFE to the outside surface of an O-ring. This coating is available in a number of colors, and can be extremely useful in an automated assembly operation. Over time, this coating can flake off, so the impact of small particulate contamination should be evaluated prior to use.For customers who so desire, Parker can coat the surface of O-rings with molybdenum disulfide (moly disulfide) or many other dry lubricants. There is a small charge for this surface coating. |
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Miscellaneous Obtain a paper copy of Parker's O-ring Handbook by calling 1-800-C-Parker or by e-mailing C-Parker@parker.com. Electronic (PDF) versions of the O-ring Handbook are not yet available. However, the Reference Guide from Parker's inPHorm software can be downloaded as a Windows help file. Save this file onto your Windows-based PC and double-click on the icon. Very seldom are the differences between seal compounds visible. Differences in the base polymer, cure system, and amount and type of other compound ingredients play a significant role in both the seal performance and the seal cost. The phrase "you get what you pay for" usually applies in the O-ring industry. Select O-rings can be ordered online. For special needs, contact your local distributor or Parker O-ring Division. Parker's inPHorm seal design software can be downloaded from the Internet. Parker provides a number of custom molded and custom engineered rubber seals through Parker O-ring Division and Parker Engineered Seals Division. |
