Machinery's Handbook, 31st Edition
2682 O-RINGS standard glands set the inner diameter minimum as equal to the O-ring nominal inner diameter. The SAE system allows up to 5 percent stretch, while the ISO system allows up to 8 percent stretch of the squeezed O-ring inner diameter. Larger stretch values can work in some applications. Axial Face Gland Calculations: When working with standard gland dimensions, the designer usually begins with a preferred cross section and inner diameter. Standards and catalogs can then be used to determine appropriate groove dimensions. These dimensions can be customized if desired, but the resulting O-ring stretch/cramping, squeeze, and gland fill must be evaluated to check for potential problems. Standard gland dimensions include some violations of standard recommended squeeze ranges. In the standards, tar- get squeeze ranges are as follows: SAE Sizes -0XX: 10–25% SAE Sizes -1XX and -2XX: 10–20% SAE Sizes -3XX: 10–18% SAE Sizes -4XX: 10–17% ISO Sizes -0XXA: 21–36% ISO Sizes -1XXA: 19–30% ISO Sizes -2XXA: 17–26% ISO Sizes -3XXA: 15–23% ISO Sizes -4XXA: 13–20% In axial face glands, most O-ring stretch/cramping occurs after it is squeezed and wid- ens to interfere with (deform against) the groove wall. When an axial face gland is closed, the O-ring cross section is squeezed into an oval shape with length L. Assuming that the nominal mean diameter of the O-ring does not move, the squeezed O-ring inner diameter reduces and the outer diameter expands. This causes the O-ring to stretch and/or cramp in the gland, putting it in good contact with the groove walls and preventing movement of the O-ring. The following equations, which apply to Fig. 2, can be used to calculate stretch/ cramping, squeeze, and gland fill for many elastomeric O-rings: Definition of variables: ID = O-ring inner diameter W = O-ring cross section diameter AF = gland depth WR = reduced O-ring cross section in axial gland IDG = face groove inner diameter ODG = face groove outer diameter AG = groove width L = length of axially squeezed O-ring cross section ASID = axially squeezed O-ring inner diameter ASOD = axially squeezed O-ring outer diameter GVol = groove volume OVol = O-ring volume Fill % = gland fill percent AStretch % = inner diameter stretch (external pressure) Sq % = axial O-ring squeeze percentage ACramp % = outer diameter cramping (internal pressure) For Axial Glands: WR min = W min WR max = W max L AF W AF AF max min nom min min = − ( ) + 4 2 2 L AF W AF AF min max nom max max = − ( ) + 4 2 2 ASID max = ID nom + W nom – L min ASID min = ID nom + W nom – L max ASOD max = ID nom + W nom + L max ASOD min = ID nom + W nom + L min AStretch % max = (( IDG max – ASID min )/ ASID min ) × 100% AStretch % min = (( IDG min – ASID max )/ ASID max ) × 100% ACramp % max = (( ODG min – ASOD max )/ ASOD max ) × 100% ACramp % min = (( ODG max – ASOD min )/ ASOD min ) × 100% AF max = AF max (given) AF min = AF min (given) Sq% max = (( WR max – AF min )/ W max ) × 100% Sq% min = (( WR min – AF max )/ W min ) × 100% OVol max = max max max 2 2 4 × + × ( ) ( ) ID W W ( ) OVol min = min min min 2 2 4 × + × ( ) ( ) ID W W ( ) Vol max = max min max 4 × – × ( ) ODG IDG AF ( ) 2 2 GVol min = min max min 4 × – × ( ) ODG IDG AF ( ) 2 2 Fill % max = ( OVol max / GVol min ) × 100% Fill % min = ( OVol min / GVol max ) × 100%
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