Static seals are categorized as either AXIAL or RADIAL, depending upon the direction in which squeeze is applied to the O-ring's cross section.
A static axial seal acts similar to a gasket in that it is squeezed on both the top and bottom of the O-ring's cross section. This type of seal is typically employed in the face (flange) type applications, depicted in Illustration 4.1.
When used as a face seal involving either internal or external pressure, the O-ring should always be seated against the low pressure side of the groove (as shown in Illustration 4.1 & Illustration 4.2) to minimize O-ring movement and accompanying wear within the groove.
Static axial seals tend to be easier to design than static radial seals. Since there is no extrusion gap, there are fewer design steps and you can control the tolerances easier.
Table B lists SAE recommended dimensions for static axial seal glands by ascending AS 568* O-ring - numbers.
Static Radial Seals are squeezed between the inner and outer surfaces of the O-ring. They are typically employed in cap and plug type applications, as depicted in Illustration 4.3.
Table C lists SAE recommended dimensions for static radial seal glands by ascending AS 568* numbers.
Recommended dimensions for static radial seal glands listed in Table C are based on an application pressure limit of 1500 psi.
In crush seal applications, the O-ring is completely confined and pressure deformed (crushed) within a triangular gland made by machining a 45° angle on the male cover. Squeezed at an angle to the O-ring's axis, crush seals are used in such simple applications as the one depicted in Illustration 4.4.
Table D lists SAE recommended dimensions for static crush seal glands by ascending AS 568* numbers.
O-rings are sometimes employed in static or slow moving dynamic situations calling for specially machined "dovetail" glands. Because of the angles involved, controlling the tolerances in these glands may be difficult. The purpose of these glands is to securely hold the O-ring in place during machine operation and/or maintenance disassembly. A typical valve seat application is shown in Illustration 4.5.
In this application O-ring squeeze is primarily axial in direction (as valve operation exerts force on top and bottom seal surfaces). To avoid tearing or nicking, the use of O-ring lubrication is recommended while installing the O-ring into the dovetail gland. Because of the difficulty in creating the groove and tight tolerances required, this type of seal application should only be used when necessary.
Table E lists SAE recommended dimensions for dovetail glands by ascending AS 568* numbers.