O-Ring Reference: AS568 Sizes - All Seals Inc.

1 Your Technology SpecialistO- ring reference : AS568 SizesAS568 O-Ring size ReferenceFreudenberg and NOK Group1 The Simrit O-Ring Design Quick ReferenceThis design quick reference guide is intended for use in specifying O-Ring and groove dimensions for staticapplications with pressures less than 1500 guidelines are for the nominal condition. The minimumand maximum conditions should also be checked. Thisrequires looking at the dimensionally largest possible O-Ring in the smallest possible groove ( , at the hard-ware and O-Ring tolerance stack-up) and the smallestpossible O-Ring in the largest possible Gland Types and NomenclatureMost static O-Ring Seals can be classified into one of thethree arrangements shown below.

2 The variable namesPiston-Type SealFace-Type SealRod-Type SealPistonGlandBoreHWRodGlandBoreHWInOut HWThroughout this reference guide the term compression is used for describing what provides the sealing elastomers are essentially incompressible, the technically correct term would be deformation. Compression is used, as it is the more commonly used terminology in the in these diagrams are used throughout thequick reference Dimension CalculationsAlthough each physical arrangement is different, typicallythe O-Ring is captured in a rectangular gland. Twoopposing surfaces are sealing surfaces, in that the distance between them, the gland height (H), is less thanthe O-Ring cross-section (CS) so that the installed O-ringis compressed, resulting in a sealing force.

3 The other twoO- ring DimensionsGland DimensionsGland Width (W)Sealing SurfaceContaining SurfaceContaining SurfaceSealing SurfaceGland Height (H)CSODIDP iston-Type SealBore Gland H = W = W2 Rod-Type SealGland Rod H = W = W2 Face-Type SealOut In H = H W = 2 Piston-Type SealGland ID Stretch = IDRod-Type SealOD Gland Interference = ODExternal Pressure Face-Type SealIn ID Stretch = IDInternal Pressure Face-Type SealOD Out Interference = ODID Stretch/OD InterferenceThe ID or OD of the O-Ring should be chosen to minimizethe potential for installation damage and to minimize wearduring piston-type Seals the ID of the O-Ring should besmaller than the gland diameter so that the installedO- ring is always slightly stretched.

4 Even with thelargest possible O-Ring ID and smallest possiblegland rod-type Seals the OD of the O-Ring should beslightly larger than the glanddiameter so that there isalways some = 5 %Minimum = 0 %Maximum = 2 %Minimum = 0 %Maximum = 5 %Minimum = 0 %Maximum = 3 %Minimum = 0 %opposing surfaces are containing surfaces in that the distance between them, the gland width (W), is largerthan the O-Ring cross-section so that they serve to keep theO- ring in place. Calculations of basic gland dimensionsfor piston type, rod type and face Seals are shown external pressure face Seals , the ID of the O-ringshould be slightly smaller than the inner diameter (In)so that when the pressure is applied, the O-Ring isalready where it would be as a result of the internal pressure face Seals , the OD of the O-ringshould be slightly larger than the outer diameter (Out)so that when the pressure is applied, the O-Ring isalready where it would be as a result of the in Cross-SectionSince elastomers are essentially incompressible materials,if the ID of the O-Ring is stretched, the cross-section of the O-Ring will decrease.

5 The following tables give theO- ring cross-sections that result from ID stretch. The newcross-section should be used for all compression andAS568 Original Cross-Section Reduced Cross-Section at Seriesin Inches% ID Stretch (inches)1%2%3%4%5%- Cross-Section Reduced Cross-Section at Seriesin Millimeters% ID Stretch (millimeters)1%2%3%4%5% SqueezeCompression squeeze is the difference between the originalO- ring cross-section (CS) and the gland height (H). It isexpressed in either inches or SqueezeCalculationCompression Squeeze = CS HRecommended Minimum ValueCompression Squeeze > inch ( mm)Compression SqueezeCSHgland fill calculations for piston-type and external pressure face impact of OD interference on the O-Ring cross-sectionvaries and does not typically require design RatioThe compression ratio is the ratio between compressionsqueeze and the uncompressed O-Ring ValuePiston- or Rod-Type SealMinimum: 5%Target: 20%Maximum: 30%Face-Type SealMinimum: 10%Target: 25%Maximum: 35%CalculationCompression Squeeze Compression Ratio (%) = x 100 CSGland FillGland fill is the percentage of the gland that is occupied by the O-Ring .

6 It is calculated by dividing The following target gland fill recommendations take intoaccount several hardware and O-Ring -related factorsincluding but not limited to thermal expansion, volumeswell due to fluid exposure, and the effect of toleranceO- ring Cross-Section AreaGland Cross-Section AreaGland FillCS 2 O-Ring CSA = x()2 Gland CSA = H x W *Recommended ValuesTarget Minimum: 65%Target: 75%Target Maximum: 85% O-Ring CSA Gland Fill (%) = x 100 Gland CSAO-RingCSACSG landCSAWH* Effect of gland angle not addressedCompression ratio is typically expressed as a cross-sectional area (CSA) of the O-Ring by the cross-sectional area of the A gland fill as low as 50% and as high as90% is acceptable, but it is recommended that the targets shown below be adhered to whenever GapExtrusion is a concern for radial Seals where there is agap between the piston and the bore for a piston-typeseal or between the rod and the bore for a rod-typeseal.

7 It is not typically a concern for face Seals where themetal parts to be sealed are in contact line-to-line. Theissue is that at higher pressures and especially for softerPiston-Type SealExtrusion Gap = Bore PistonRod-Type SealMaximum Recommended Extrusion Gap in Inches (mm)Extrusion Gap = Bore RodConcentricity and Diametric ClearanceExtrusionPressure Elastomer Hardness (PSI)(Durometer) (.25).015 (.38).020 (.51).025 (.64) (.13).011 (.28).016 (.41).023 (.58) (.05).008 (.20).012 (.30).018 (.46) (.02).004 (.10).009 (.23).015 (.38)1500 Consult (.05).007 (.18).012 (.30)ExtrusionGapMaximum Possible Extrusion GapHighPressureFor pressures greater than 1500 psi consult elastomers, the O-Ring can be forced by the pressure into the small gap between the piston or rodand the bore.

8 Unless the hardware can ensure the boreand the piston or rod remain concentric, we have toassume that all of the gap possible can shift to one side (see diagram below).6 Other Groove DetailsInstallation AidsInstallation Chamfer LengthGroove Detail DiagramDetailInchmmWall Angle0 to 5 0 to 5 Break to . to .25 Static Sealing32 mSurface FinishmaximummaximumStatic Contain64 mSurface FinishmaximummaximumRadiusSee table belowAS568 RadiusRadiusSeries(inch)(mm) addition to proper compression and gland fill, a properly designed and machined gland is essential for agood O-Ring seal. The tables at the right and the diagrambelow provide the recommended gland design parame-ters. In addition, the gland surfaces must be free from allmachining irregularities, and the gland edges should besmooth and true and free of nicks, scratches, and perfectly designed O-Ring seal is of little use if the O-Ring is damaged during installation.

9 To prevent installation damage for piston-type and rod-type Seals ,we recommend a 15 chamfer on the bore or rod. TheRadiusContaining SurfaceBreak EdgeSealingSurfaceWallAngleSealing SurfaceAS568O- ring CSChamfer LengthSeriesInchesmmInchesmmchamfer must be long enough to ensure that the O-ringsees only the chamfer when it is installed. Face-typeseals do not require design considerations beyond thegroove detail recommendations offered of Commonly Used ElastomersMaterial NameSimriz SuperAflasFluoro-Ethylene NitrileSilicone Fluoro-FKMcarbonPropylenesiliconeASTM D1418 DesignationFFKMETPTFE/PFKMEPDMNBRVMQFVMQ T ypical ColorsBlack Black Black BlackBlackBlackRedBlueWhiteWhiteWhitePur pleWhiteClearBrownGreenOPERATING TEMPERATURE RANGELow Temperature 20 C 20 C 10 C 40 C 55 C 50 C 75 C 65 C 4 F 4 F+14 F 40 F 67 F 58 F 103 F 85 FHigh Temperature300 C200 C200 C250 C150 C120 C230 C180 C572 F392 F392 F482 F302 F248 F446 F356 FPHYSICAL PROPERTIESA brasion Resistance32221244 Permeation Resistance22212244

10 Compression Set Resistance22212111 Tear Resistance33331244 CHEMICAL COMPATIBILITYI norganicAcids11111232 Bases12141233 OrganicAcids11111232 Alcohols11131111 Aldehydes12431324 Amines22141424 Aromatic Hydrocarbons11414341 Ether13443443 Halogenides21414444 Ketone13441444 Water11111111 Steam (<149 C/300 F)12221434 Steam (>149 C/300 F)23344444 Material Rating: 1 Little or no effect (volume change <10%) 2 Possible loss of physical properties (volume change 10 20%) 3 Noticeable change (volume change 20 40%) 4 Excessive change (volume change >40%) 0 Insufficient information 8 Elastomer MaterialsSimriz PerfluoroelastomerDesignation:FFKMD escription:Excellent resistance to all outgassing performance in vacuum :Avoid low-molecular-weight, fully halogenatedfluids and molten alkali metals.