Machinery's Handbook, 31st Edition
O-RINGS
2687
Calculate: F max = 0.093
F min = 0.085
( F max = 2.218)
( F min = 2.102)
Stretch % max = 3.2% AR % max = 1.6%
Stretch % min = 0.4% ( Stretch % max = 3.7%)
( Stretch % min = 1%) ( AR % min = 0.5%) ( WR min = 2.483) ( Sq % max = 22%) ( GVol min = 543.02) ( Fill % min = 56.5%)
AR % min = 0.2% WR min = 0.098 Sq % max = 20% GVol min = 0.032 Fill % min = 58%
( AR % max = 1.8%) ( WR max = 2.697) ( Sq % min = 11%) ( GVol max = 587.69) ( Fill % max = 72.3%)
WR max = 0.106 Sq % min = 6% GVol max = 0.035 Fill % max = 73%
Validate for the -116 SAE O-Ring: Stretch % max = 3.2%
Stretch % min = 0.4% Well within SAE limit of 5%.
Sq % min = 6% Fill % max = 73%
Sq % max = 20% Fill % min = 58%
Meets SAE recommendation of 5–21% for this cross section.
Within SAE target maximum of 85%.
Validate for the -116A ISO O-Ring: ( Stretch % max = 3.7%) ( Stretch % min = 1%)
Well within ISO limit of 5%.
( Sq % min = 11%)
( Sq % max = 22%)
Meets ISO recommendation of 8–22% for this cross section.
( Fill )% max = 72.3% ( Fill )% min = 56.5% Within ISO target maximum of 85%. Floating Piston Glands: In pneumatic reciprocating applications, where friction (mani- festing as drag and/or heat) is a critical consideration, a “floating” piston gland design can be beneficial because it applies zero stretch to the O-ring. The gland is located on the piston and is overly deep to avoid contact with the O-ring and allow some radial flotation. Groove width is reduced by about 20 percent to help prevent axial movement in the ab- sence of stretch. All compression of the O-ring happens at the outer diameter, where it in- terferes slightly (called “cramping”) with the housing bore. The amount of recommended cramping increases with O-ring cross section. Some recommended cramping values for floating piston glands are as follows: Here, floating piston gland cramping = O-ring nominal outside diameter – housing bore diameter minimum Floating piston glands are suitable for low-pressure hydraulics below 200 psi (1.38 MPa) that allow for some leakage. Pneumatic piston glands also can be designed to float, but floating pneumatic rod glands have drag problems due to rod-induced stretch and there - fore are not recommended. Each time the direction of pressure changes and the O-ring moves from one side of the groove to the other, fluid or gas can travel under and around the seal until the O-ring is again in contact with a groove wall. Lubrication is needed for pneumatic applications. Rotary Motion Radial Seals: Lip seals and other engineered seals generally work best in rotary applications, but O-rings made of wear-resistant, hard material may be used with caution. Rotary O-ring applications are configured with the groove in the housing bore to prevent centrifugal expansion of the O-ring. The shaft should rotate inside the O-ring, and squeeze must be kept very low. Groove diameter normally is sized 5 percent smaller than the O-ring outer diameter to prevent rotation of the O-ring and cramp it against the shaft. The shaft must be supported with bearings, with the O-ring simply acting as a seal. This application requires reliable lubrication and heat management. Sizes -006 to -012: Cramping = 0.033–0.040 in. (0.8–1.0 mm) Sizes -104 to -116: Cramping = 0.036–0.060 in. (0.9–1.5 mm) Sizes -201 to -222: Cramping = 0.059–0.080 in. (1.5–2.0 mm) Sizes -309 to -349: Cramping = 0.082–0.122 in. (2.1–3.1 mm) Sizes -425 to -460: Cramping = 0.138–0.173 in. (3.5–4.4 mm)
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