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more than 30 years of solving problems fordiverse industries and applications. Capabilitiesinclude concurrent engineering, completeproject management, computer aided design,expertise in polymer technology and othermaterials and prototyping to drastically reducedevelopment cycle time.»Research and DevelopmentIt is our obligation to provide the best sealingsolutions of tomorrow as well as today.Confronted continually by the challenges ofnew applications from industries as diverse asmedical, electronics and automotive, we arealways exploring new designs, new materials andnew processes.»Customer ServiceWith direct access to Apple Rubber’sknowledgeable sales team, design engineers andQC staff, you have the “source” working for you.No middlemen – no confusion – no games.»Comprehensive ManufacturingTechnologiesAn unparalleled range of capabilities and fullyintegrated manufacturing facilities includingtransfer molding, compression molding, liquidsilicone molding, plastic injection molding,rubber injection, CNC machining and proprietarybonding processes. Manufacturing is performedin our US plant located in Lancaster, NY.»ISO 9001 RegistrationApple Rubber earned ISO 9001 Registration.The scope of our ISO 9001 Registration, themost comprehensive standard of the ISO 9000series, covers the design and manufacture ofsealing components for various applicationsincluding aerospace, automotive and medical8»APPLE RUBBER PRODUCTS AND SERVICESAS9100Apple Rubber’s quality managementsystem meets the requirements of AS9100,Quality Management Systems - Aerospace- Requirements. AS9100 incorporatesthe requirements of ISO 9001 and addsrequirements specific to the aerospace industry.PrototypingWe have the experience and advanced processesto respond quickly to prototype requirements,helping you to drastically reduce design anddevelopment time.»products. ISO 9001 Registration is testimonyto Apple Rubber’s commitment to offeringthe highest quality seals and sealing devicesavailable. Apple Rubber actively participates inongoing certification updates. Check our websitefor the most current certification listings anddocumentation.»Quality Assurance and TestingApple Rubber’s advanced testing laboratoryoffers one of the most stringent qualityassurance programs in the industry. Materialand dimensional certifications are available.We can customize a quality program to meetyour specific testing requirements and supplydocumentation with shipments.

3O-Ring BasicsSEAL THINKINGTMElastomer seals are unlike any other materials thatdesign engineers confront. Metal or plastic parts, forinstance, are probably failing if visibly distorted. But,an o-ring must be deformed to function properly. Infact, an o-ring that is not squeezed and stretched in itsapplication is the wrong o-ring.DEFINITIONAn o-ring is a doughnut-shaped object, or torus. Theopposite sides of an o-ring are squeezed between thewalls of the cavity or “gland” into which the o-ring isinstalled. The resulting zero clearance within the glandprovides an effective seal, blocking the flow of liquidsor gases through the gland’s internal passage.An o-ring is defined by its dimensions (based oninside diameter and cross section), durometer(Shore A hardness), and material composition.Illustration 3.1 demonstrates three applicationsshowing the two basic categories of o-rings: static,contained within a non-moving gland as in a face seal,and dynamice, contained within a moving gland as ina piston or rod seal.WHY AN O-RING WORKSAs Illustration 3.1 shows, a properly designed sealingsystem incorporates some degree of initial o-ringcompression. At atmospheric pressure, only theresiliency of the compressed o-ring provides the seal.However, as system pressure activates the seal, theo-ring is forced to the low pressure side of the gland.Designed to deform, the o-ring “flows” to fill thediametrical clearance and blocks any further leakage.Illustration 5.1 in section 5 shows a progressiveapplication of pressure and the effect it has onthe seal. Pressure, as well as many otherconsiderations, determine the effectivenessof a seal. These consid erations are highlightedthroughout this design guide.DIMENSIONAL CONSIDERATIONS»Inside DiameterTo provide an effective seal, the o-ring’s insidediameter (I.D.) must be smaller than the pistongroove diameter, so that the o-ring is slightlystretched, fitting snugly in the groove. This stretchshould be between 1% - 5% with 2% as the idealin most applications. A stretch greater than 5%is not recommended. The resulting stress onthe o-ring will cause accelerated aging and crosssection reduction.Exception to this rule is a floating seal. These areo-rings that are allowed to sit in grooves freelyor “float”. These are typically used in pneumaticpiston applications, where some leakage can betolerated for the benefit of lower friction.Calculate the o-ring I.D. according to the followingformula:O-RING I.D. Groove Diameter% of stretch desired 1(1% - 5%)EXAMPLEIf Groove Diameter .231Then O-Ring I.D. .231 .229 to .2201.01 to 1.05Depending on % of stretch desired9

»Cross SectionWhen calculating the cross section (C.S.) ofan o-ring, you need to consider the size ofthe gland to be filled as well as the amount ofsqueeze needed to create a good seal. Virtuallyevery gland has a slight gap between the twomating surfaces, termed “diametrical clearance.”Therefore, it is important for the o-ringcross-section to be greater than the gland depth.The resulting o-ring squeeze prevents leakage byblocking the diametrical gap.Illustration 3.1 demonstrates that in “static”face seals or “dynamic” piston and rod seals, theo-ring is being squeezed slightly within the gland.Squeeze may occur in one of two possible ways.If the squeeze occurs on the top and bottomsurfaces of the o-ring, as in face seals,it is referred to as axial squeeze. If the squeezeis on the inner and outer surfaces of the o-ring,as in piston or rod seals, it is referred to as radialsqueeze.To obtain the correct amount of squeeze foroptimum o-ring sealing, careful considerationmust be given to the size of the o-ring in relationto the size of the glandular space into which theo-ring is being installed. The actual calculationfor the cross section needed in an o-ring variesdepending on whether it will be used in adynamic or static application. In a dynamicsituation, lower squeeze is recommended toreduce friction.10APPLE RUBBER O-RING BASICSFaceAxialSeals(C 0)ABDABPiston (Radial)SealC2AA - Gland DepthB - Groove WidthC - Diametrical ClearanceD - Groove DepthBRod (Radial)SealC/2Illustration 3.1, Common ApplicationsRule ofThumbA stretch greater than 5% on the o-ringI.D. is not recommended because it canlead to a loss of seal compression dueto reduced cross-section.Rule ofThumbA groove depth is the machined depthinto one surface, whereas a glanddepth consists of the groove depth plusdiametrical clearance. The gland depthis used to calculate seal compression.

ximumRING CS»Calculation of Minimum O-Ring Cross SectionDynamic (Moving) Radial SealCross Section CalculationReferring to Illustration 3.2 for term definition,and Illustration 3.3 for sample dimensions,calculating the correct o-ring cross section for aspecific gland depth is illustrated to the right. Inthe case of the dynamic piston seal shown, thecross section is calculated as follows:Calculation of Maximum O-Ring Cross Section1. Enter the bore diameter2. Subtract the bore tolerance from thebore diameter3. Enter the groove diameter4. Add the groove tolerance to thegroove diameter5. Subtract line 4 from line 26. Divide line 5 by 27. Enter the maximum % compression8. Divide line 7 by 1009. Subtract line 8 from the number 110. Divide line 6 by line 911. Enter o-ring C.S. tolerance12. Subtract line 11 from line 10for the answer1.2.3.4.5.6.7.8.9.10.11.12.Enter the bore diameterAdd the bore tolerance to the bore diameterEnter the groove diameterSubtract the groove tolerance from thegroove diameterSubtract line 4 from line 2Divide line 5 by 2Enter the minimum % compressionDivide line 7 by 100Subtract line 8 from the number 1Divide line 6 by line 9Enter o-ring C.S. toleranceAdd line 11 to line 10 for the answerStatic (Non-moving) Axial Seal CalculationMax Bore Diameter - Min Groove DiameterMinimumO-RING CS21-Min % Compression O-Ring CS Tolerance100Min Bore Diameter - Max Groove Diameter2MaximumO-RING CS1-Max % Compression– O-Ring CS Tolerance100CrossSectionDiametrical ClearanceGrooveDiameterBoreDiameterIllustration 3.2, Radial SealRule ofThumbTo create seal squeeze, the gland depthmust be less than the seal cross section.Min Bore Diameter - Max Groove Diameter21-Max % Compression100InsideDiameterIllustration 3.3, O-ring ProfileTo calculate the cross section of an axialseal, determine the gland depth and thenmultiply by the maximum and minimumsqueeze requirements, noting to add 1.00 tothe recommended squeeze. For example, arecommended squeeze of 30% would translateto a multiplied factor of 1.3.The o-ring I.D. is determined by the presenceof pressure, whether from the I.D. or the O.D. Ifpressure forces the o-ring towards the inside, asshown in Illustration 4.2, then the o-ring shouldbe designed with the I.D. close to the grooveI.D. However, if pressure forces the seal to theoutside, as shown in Illustration 4.1, then theseal should incorporate some inference onthe O.D.– O-Ring CS Tolerance11

MATERIAL CONSIDERATIONSFRICTIONAfter you have determined the o-ring size, you willthen have to select the appropriate o-ring material.Listed in Section 6, “Material Selection Guide,”are various elastomers including statements ofdescription, key uses, temperature ranges, featuresand limitations. Prior to seal purchase, make sure totake into account all of the factors discussed below.In addition, you might want to consider availabilityand cost (see Section 6). If a material is not shown,contact Apple Rubber for availability.There are two types of friction, both of which areimportant considerations in dynamic (moving)applications. When part movement is intermittent,the effects of breakout friction can cause excessivelyhigh pressures to develop. This pressure can tearportions of the seal that adhered to the gland wallcausing seal failure.CHEMICAL ATTACKA major consideration for o-ring material selectionis resistance of specific elastomers to degradationby exposure to certain chemicals. Therefore, thefirst step in material selection is to match yourapplication’s chemicals with the o-ring material thatoffers the best resistance. To do this, refer to the“Chemical Compatibility” table and the “GeneralProperties” table found on our website or Section 6of this guide.TEMPERATUREThe range of temperature experienced duringoperation is an important factor when consideringefficient sealing. It is particularly important tomeasure temperature in the immediate o-ringenvironment, not just the system temperature. Youmust also consider the length of exposure to anyhigh temperature, whether it involves short bursts orlong, sustained levels.The temperature ranges for various o-ring materialsare listed in Section 6, “Materials Selection Guide,”as well as graphed in Section 5, “Critical OperatingEnvironmental Factors.” The Material Selection Guideon our website allows users to enter a range to findthe correct material.12APPLE RUBBER O-RING BASICSIn continuously moving applications, excessiveo-ring running friction can cause heat to build upwithin the o-ring material itself. This causes swelling,which causes more heat to develop, and eventuallyresults in material degradation and failure. For moreinformation, consult Section 5.DUROMETERDurometer (Shore A) is a measurement of thehardness of an elastomeric compound. Thenumerical ratings for hardness run from lowernumbered (less than 70) softer materials to highernumbered (greater than 70) harder materials,noting that fluorocarbon has a base rating of 75.This classification system is designed to work withina 5 point range. All materials are not available inall hardnesses. Please refer to Section 6, “MaterialSelection Guide,” for the range of individualelastomers.PRESSUREThe presence of high pressure on an o-ring canjeopardize its ability to seal. For correct o-ring designin high pressure situations, see Section 5, “ExtrusionLimit” chart.However, low pressure can present a problem aswell. If the system pressure is below 100 psi, it isclassified as low pressure. Because system pressureis not great enough to “activate” the seal, the designmust rely solely on the resiliency of the elastomerRule ofThumbThe maximum volume of the o-ringshould never surpass the minimumvolume of the gland.Rule ofThumbStatic applications are more tolerantof material and design limitationsthan dynamic applications.

to retain its original compressive force. Over time,the elastomer may not resist compression as muchand take a compression “set,” resulting in possibleseal failure. However, by proper component designwhich may include lowering the seal durometeror increasing the o-ring cross section, maximumseal utility is achieved. For an illustration of thisrelationship, see Section 5.005”(.13mm)Max.003”(.08mm)MaxSUMMARYFor optimum sealing performance, correct o-ringselection is the direct result of a number of designconsiderations. These considerations include: size,squeeze, stretch, chemical compatibility and theability to resist pressure, temperature and friction.All of these points of o-ring design are covered indetail within the sections of this Design Guide. Formore information on any of these points, see theappropriate sections. Often, there are a numberof materials that are appropriate for a particularapplication. Consideration should be given to the fullrange of environmental and cost factors. Your finalselection will usually be a compromise in the sensethat you have to balance all of these considerations.Illustration 3.4, O-ring ProfilePARTING LINE PROJECTIONParting line projection is a continuous ridge ofmaterial located on the parting line at the ID andOD of the o-ring. This is often caused by mold wearcreating enlarged radii from the mold cavity to the flatplane of the tool.EXCESSIVE FLASHExcessive flash is a thin, film-like layer of materialextending from the parting line projection, oftencaused by mold separation or inadequate de-flashing.The standard acceptable flash shown in Illustration3.4 is .005” thick and .003” extension.PLEASE NOTE THE FOLLOWINGThe applications, suggestions and recommendationscontained in this book are meant to be used as aprofessional guide only. Because no two situationsor installations are the same, these comments,sug gestions, and recommendations are necessarilygeneral and should not be relied upon by any purchaserwithout independent verification based on the particularinstallation or use. We strongly recom mend that the sealyou select be rigorously tested in the actual applicationprior to production use.13

Seal Types and Gland Design4MAJOR CLASSIFICATIONSAll o-ring seal applications are categorized in terms of relative motion. In situations involving little or nomotion relative to the seal, the o-ring application is static. In situations involving reciprocating, rotating,or oscillating motion relative to the seal, the o-ring application is dynamic.ASTATIC SEAL TYPESStatic seals are categorized as either axial or radial,depending upon the direction in which squeeze isapplied to the o-ring’s cross section.» Static Axial SealA static axial seal acts similar to a gasket in thatit is squeezed on both the top and bottom of theo-ring’s cross section. This type of seal is typicallyemployed in the face (flange) type applications,depicted in Illustration 4.1.PWhen used as a face seal involving eitherinternal or external pressure, the o-ring shouldalways be seated against the low pressure sideof the groove (as shown in Illustration 4.1 andIllustration 4.2) so the o-ring is already where itneeds to be as a result of the pressure.Static axial seals tend to be easier to design thanstatic radial seals. Since there is no extrusiongap, there are fewer design steps and you cancontrol the tolerances easier.Illustration 4.1, Internal PressureBPPstatic axial seal gland dimensionsTable B lists SAE recommended dimensionsfor static axial seal glands by ascending AS568o-ring numbers.Illustration 4.2, External Pressure14APPLE RUBBER SEAL TYPES AND GLAND DESIGN

» Static Radial SealsStatic Radial Seals are squeezed between theinner and outer surfaces of the o-ring. Theyare typically employed in cap and plug typeapplications, as depicted in Illustration 4.3.45 static radial seal gland dimensionsTable C (p. 30-44) lists SAE recommendeddimensions for static radial seal glands byascending AS568 numbers.NOTE: Recommended dimensions for static radial sealglands listed in Table C are based on an applicationpressure limit of 1500 psi. For higher pressurerequirements, reference Section 5, Illustration 5.1or contact Apple Rubber for technical assistance.Illustration 4.4, Static Crush Seal»Static Seals with Dovetail GlandsO

The Apple Rubber Seal Design Guide was first published in 1989 and quickly became more popular and successful than we could have ever hoped, with thousands of copies distributed. This guide reflects the dynamic growth of Apple Rubber and our commitment to continually bring you new ideas and technologies in seals and other elastomeric products.