O-Ring compression is a result of three factors: the force applied to compress the seal, durometer, and cross section. These relationships are demonstrated in Illustration 5.3. Additionally, o-ring stretch affects seal compression by reducing cross section, which reduces the sealing potential of the o-ring. This relationship is demonstrated in the equation below.
The calculated value assumes the o-ring volume does not change and the cross-section remains round when stretched.
Illustration 5.3 is comprised of a great deal of information regarding o-ring compression. Within the body of the graph are the various durometers for standard cross sections. Nonstandard cross sections and omitted durometers can be inferred from the generally linear relationship between the amount of applied compressive force and seal compression, durometer and cross section.