Static Male and Female O-ring Seal Design
Design Chart 4-2 and its accompanying Design Table 4-2 (available by clicking on the chart image at the bottom of the page) give one set of dimensions for static O-ring seals when the configuration is similar to a piston or rod application with no motion involved.
For applications requiring more than two or three percent stretch on the inside diameter of the O-ring, refer to the figure below to determine the effective “W” dimension for the stretched ring. The desired percent squeeze should be applied to this cross section diameter. In large male gland assemblies, it may be desirable to use an O-ring one size smaller than indicated in the design chart. The design stretch is so small in these large sizes that the O-ring tends to sag out of the groove before it is assembled. Using the next smaller size simplifies assembly, but requires a reduced gland depth to attain the proper squeeze.
The need for back-up rings should be investigated for pressures exceeding 103.5 Bar (1500 psi) (for all seal types). If there is no extrusion gap, back-up rings are not required. Very high pressures can be sealed without back-up rings if metal-to-metal contact (practically zero clearance) of the gland parts can be maintained. Instances have been reported of sealing pressures of 13,600 Bar (200,000 psi) with a 70 Shore A durometer Oring without back-up rings. Vibration or pressure fluctuation sometimes will produce “breathing” which requires back-up rings at average pressures below 103.5 Bar (1500 psi). When using silicone O-rings, the clearances given in the design charts and tables should be reduced 50%.
For examples of static seals, see the figures below.
|End Cap Seal||Plug Seal|