As Illustration 3.1 shows, a properly designed sealing system incorporates some degree of initial o-ring compression. At atmospheric pressure, only the resiliency of the compressed o-ring provides the seal. However, as system pressure activates the seal, the o-ring is forced to the low pressure side of the gland.
Designed to deform, the o-ring “flows” to fill the diametrical clearance and blocks any further leakage. Illustration 5.1 shows a progressive application of pressure and the effect it has on the seal. Pressure, as well as many other considerations, determine the effectiveness of a seal. These considerations are highlighted throughout this design guide.