Compression Set Resistance

The final requirement for effective vacuum sealing involves the specification of O-ring elastomers with good compression set characteristics. Employing a seal squeeze of up to 40% inhibits media flow through the seal. This squeeze also forces the O-ring to conform to the surface irregularities of the gland, helping to further prevent leakage. Keep in mind, however, that because of the decreased groove depth, increased groove width is essential.

Best Choice(s)

In terms of compression set resistance, Fluorocarbon is rated as "good", followed by Neoprene at "fair to good", and Butyl at "fair to good".

As an added measure of leak prevention, lubrication of O-rings with vacuum grease helps to fill the microscopic pores of surrounding glandular surfaces which have been machined to the recommended 16 to 32 RMS finish.