Machinery's Handbook, 31st Edition
2686 O-RINGS standards. As an approximation, Poisson’s ratio ( µ ) with a value of 0.5 (for rubber) can be used as shown below. The following equations, which apply to Fig. 2 and Fig. 3, 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 G = groove width F = gland depth including clearance gap and groove eccentricity PISTON = outer diameter of the piston PG = diameter of a piston groove ROD = outer diameter of a rod BORE = inner diameter of the housing bore BG = diameter of a bore groove for a rod gland Stretch % = percent O-ring stretch once installed in the groove Sq % = O-ring squeeze percentage ACramp % = outer diameter cramping GVol = groove volume OVol = O-ring volume Fill % = gland fill percent WR = reduced cross section of a stretched O-ring µ = Poisson’s ratio = 0.5 (rubber) AR % = approx. cross section reduction of stretched O-ring E = groove eccentricity Note: ISO standards omit the second two terms (clearance gap and eccentricity) in cal- culating F, affecting Squeeze %. Piston Seal: Stretch % min = (( PG min – ID max )/ ID max ) × 100% Stretch % max = (( PG max – ID min )/ ID min ) × 100%
F max = (( BORE max – PG min )/2) + (( BORE max – PISTON min )/2) + ( E max /2) F min = (( BORE min – PG max )/2) – (( BORE min – PISTON min )/2) – ( E max /2) GVol max = max min max 4 2 2 × – × ( ) BORE PG G ( ) GVol min = ( ) 4
min ( ) BORE PG G max 2 2 – ×
×
min
Rod Seal: Stretch % min = (( ROD min – ID max )/ ID max ) × 100%
Stretch % max = (( ROD max – ID min )/ ID min ) × 100%
F max = (( BG max – ROD min )/2) + (( BORE max – ROD min )/2) + ( E max /2) F min = (( BG min – ROD max )/2) – (( BORE max – ROD max )/2) – ( E max /2) GVol max = max min max 4 2 2 ( ) BG ROD G ( ) × – × GVol min =
min ( ) BG ROD G ( ) × – × max 4 2 2
min
All Radial Seals: AR % min = ( Stretch % min × µ )
AR % max = ( Stretch % max × µ )
WR max = W max – (( AR % min /100) × W max ) Sq % min = (( WR min – F max )/ W min ) × 100%
WR min = W min – (( AR % max /100) × W min ) Sq % max = (( WR max – F min )/ W max ) × 100%
max ( ) ( ) ID W W ( ) × + × max max 2 2 4
min ( ) ( ) ID W W ( ) × + × min min 2 2 4
OVol max =
min =
OVol
Fill % max = ( OVol max / GVol min ) × 100% Fill % min = ( OVol min / GVol max ) × 100% As an example, calculate stretch/cramping, squeeze, and gland fill for an SAE size -116 O-ring (-116A in ISO, shown in parentheses below) in a standard pneumatic reciprocating piston gland: Given: Use gland standard SAE AS4716C-2017 (ISO 3601-2-2016): ID max = 0.746 ID min = 0.728 ( ID max = 18.95) ( ID min = 18.49) W max = 0.106 W min = 0.1 ( W max = 2.71) ( W min = 2.53) G min = 0.141 G max = 0.151 ( G min = 4) ( G max = 4.2) PG max = 0.751 PG min = 0.749 ( PG max = 19.17) ( PG min = 19.137) BORE max = 0.927 BORE min = 0.925 ( BORE max = 23.473) ( BORE min = 23.44) PISTON max = 0.923 PISTON min = 0.922 ( PISTON max = 23.42) ( PISTON min = 23.399) E max = 0.002 ( E max = 0.025)
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