ERIKS nv - O-ring Technical Handbook

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Sealing ElementsTechnical Handbook O-rings1. O-ring StandardsThe O-ring has become the world’s most popular and versatileseal due to its simple shape, low space requirements, andits availability in a vast selection of sizes and compounds tomeet every industrial requirement.The ERIKS O-ring manual is intended as a guide to assist inthe selection of the best O-ring out of the correctrubber compound in the right application for engineers, purchasers,and other users of O-rings. We hope that you find itboth convenient and helpful.This book contains detailed information concerning elastomericcompounds, installation information, sizing tables, andgroove dimensions.The dimension tables represent standards available fromERIKSinventories.These O-rings are manufactured in accordance with a varietyof standards for each country:2. O-ring Sealing PrinciplesO-rings are bi-directional seals, circular in shape and cross section.O-rings are generally made of an elastomeric material, but maybe made of other materials such as PTFE or metal. This handbookdeals entirely with elastomeric O-rings and PTFE encapsulatedelastomeric O-rings.An O-ring seals through the deformation of the seal material byinstallation and media pressure to close off the gap betweenmating components. Higher system pressures can cause deformation through thegap, known as extrusion, resulting in seal failure. Choosing aharder seal material fig 1-3 or installing back-up rings to support theO-ring may alleviate this problem. media• AS 568A• BS 1806• DIN 3771• SMS 1586• AFNOR 47501• JIS B2401• ISO 3601USAEnglandGermanySwedenFranceJapanInternationalMedia mediaThere are also military material specifications per a “MIL”designation and aerospace material specifications per a“AMS” designation.Our standard program covers 30.000 sizes in a large varietyof rubber compounds for your specific purpose. Technicaldata and advice are available at any time. Many non-standardsizes are available upon request.Please contact your ERIKS representative.Our qualified staff guarantees excellent service. It’s our goalto be your partner.ERIKS O-rings are precision seal components made from a varietyof elastomeric compounds .When you specify an O-ring we need to know the inside diameter(I.D.), the cross section diameter (W), and the compound(elastomer Media material) from which the O-ring is to be made.All sealing applications fall into one of two categories - those inwhich the seal or sealed surface moves, and those in which theseal is stationary.ID= O-ring inside diameterw= O-ring cross sectionIDw3All the information in this documentation has been compiled with the greatest of care.Despite this we can bear no responsibility whatsoever for any errors present in the documentation. The recommendations are intended as guidelines.www.eriks.info
Sealing ElementsTechnical Handbook O-rings2. O-ring Sealing PrinciplesA seal that does not move, except for pulsation caused by cyclepressure, is called a static seal. Those seals that are subjectedto movement are dynamic seals. These are further defined asreciprocating (seals exposed to linear motion) and rotary (stationaryseals exposed to a rotating shaft).O-rings can be successfully used in static as well as dynamicapplications. The rubber O-ring should be considered as anincompressible, viscous fluid having a very high surface tension.Whether by mechanical pressure from the surrounding geometryor by pressure transmitted through the hydraulic fluid or gas,this extremely viscous (elastomeric) fluid is forced to flow in thegland to produce zero clearance or a positive block to the flow ofthe media being sealed. The O-ring absorbs the stack-up of tolerancesof the unit and its memory maintains a sealed condition.Proper seal design begins with the careful consideration of thesealing application. Appropriate material hardness, for example,is determined by the friction and pressure to which the seal willbe exposed, as well as the cross sectional dimensions of theseal. Other key factors include temperature range, adjacent surfaces,and media.Dynamic O-rings may fail by abrasion against the cylinder or pistonwalls. Therefore, the contacting surfaces should be polishedfor long seal life. Moving O-rings that pass over ports or othersurface irregularities while under pressure are quickly damaged.In designing an O-ring seal, there are usually several standardcross sectional sizes available. Selecting the best cross sectiondepends on the application. In a reciprocating application, thechoice is automatically narrowed because the design tables donot include all the standard O-ring sizes. For any given pistonor rod diameter, rings with smaller cross sections tend to twistin the groove while in motion. This leads to leakage and failure.The smaller cross sections for each inside diameter are thereforeomitted in the reciprocating design tables. For dynamic applications,the largest cross sectional sizes available should be used toincrease stability.O-rings in reciprocating applications must be radial compressedbetween the bottom of the seal groove and the cylinder wall forproper sealing action. This compression or squeeze may causethe O-ring to roll slightly in its groove under certain conditions ofmotion, but the rolling action is not necessary for normal operationof the seal.The shape of the groove is unimportant as long as it results inproper squeeze of the O-ring.Groove dimensions are shown in the tables beginning on page138. The groove depth is measured including the gap.4All the information in this documentation has been compiled with the greatest of care.Despite this we can bear no responsibility whatsoever for any errors present in the documentation. The recommendations are intended as guidelines.www.eriks.info
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