Machinery's Handbook, 31st Edition
O-RINGS 2685 Table 12. Dovetail and Half-Dovetail Groove Dimensions for Static Face Seals
Note: Sizes -0XX to -1XXA are not recommended for these grooves. Note: Sizes -2XX to -2XXA should be used with caution in these grooves.
maximum housing diameter, target a maximum cramping of 1 percent of nominal O-ring dimensions at nominal squeeze in the SAE system or 5 percent in the ISO system for O-rings with an inner diameter less than 250 mm. Larger diameter metric O-rings are allowed only 3 percent cramping. Stretch on the rod is normally limited to 5 percent. It is sometimes acceptable to violate these limits, and standards commonly include such cases for smaller sizes. Piston Glands: To design a piston gland, it is best to start with a known housing bore diameter. Piston glands have a groove cut into the outer diameter of a piston, where the O-ring is stretched slightly around the groove diameter and squeezed radially between the groove floor and housing bore. One exception to this is a pneumatic “floating” piston gland, discussed later. In most piston seal applications, limit maximum installed stretch of most elastomeric O-rings to 5 percent for long seal life. This can be exceeded for some small sizes, and standard gland dimensions include such exceptions. Radial Gland Calculations: Designers usually begin a radial seal design with a preferred cross section and inner diameter selected to work with a given rod or bore. Standards and catalogs can then be used to determine appropriate gland dimensions. In the standards, target squeeze ranges are as follows: SAE Sizes -0XX: 5–30% SAE Sizes -1XX: 5–21% SAE Sizes -2XX: 4–20% SAE Sizes -3XX: 4–17% SAE Sizes -4XX: 7–17% ISO Sizes -0XXA: 14–35% (static) 10–24% (pneumatic reciprocating) 13–27% (hydraulic reciprocating) ISO Sizes -1XXA: 13–30% (static) 8–22% (pneumatic reciprocating) 12–24% (hydraulic reciprocating) ISO Sizes -2XXA: 13–30% (static) 7–20% (pneumatic reciprocating) 11–22% (hydraulic reciprocating) ISO Sizes -3XXA: 12–28% (static) 7–18% (pneumatic reciprocating) 11–20% (hydraulic reciprocating) ISO Sizes -4XXA: 10–25% (static) 6–17% (pneumatic reciprocating) 9–19% (hydraulic reciprocating) Radial gland depth used to calculate squeeze should take into account any clearance gap and groove eccentricity E. The radial clearance gap maximum and minimum are seen when the piston or rod is side-loaded and touching the wall of the bore. While SAE standards include these factors in squeeze range calculations and recommendations, ISO standards do not. Calculation by either method is valid, as long as it is compared with recommended ranges calculated the same way. (Calculated squeeze values given in tables here take clearance gap and eccentricity into account; as a result, some squeeze values shown may be outside ISO recommended ranges.) Gland data for appropriate size ranges are given in Table 2, Table 3, and Table 6 to Table 11. 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. Pre - cise calculation methods for a radially stretched O-ring cross section are included in the
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