O-Ring Machining Specifications

The I.D. and O.D. of an O-ring gland is mainly influenced by diameter of the mating surface of the rod or piston and bore. The cross-section of the O-ring is seen as moderately arbitrary, as there are a few distinct advantages to either a larger or smaller cross-section O-Ring. Listed below are the advantages of small cross-sections and the advantages of large cross sections:

Most commonly O-rings are used to prevent the loss of a fluid or gas, however, O-rings are also useful as dust seals, drive belts, or on rotating shafts. O-rings follow the following arrangements:

Where there is a gap between the piston and the bore for a piston type seal or between the rod and the bore for a rod type seal, extrusion becomes a concern for radial seals. Extrusion gaps are not commonly a concern for face type seals where the metal parts to be sealed are in contact line-to-line. Higher pressures and especially for softer O-ring elastomers, higher pressure becomes the key issues. The O-ring can be completely forced by the pressure into the small gap between the piston (or rod) and the bore. This is unless the bore and the piston (or rod) are ensured to remain concentric by the hardware, we have to assume that entire possible gap can shift to one side. For additional detail, please see the diagram below.