Resistance to Fluid
As used throughout this handbook, the term “fluid” denotes the substance retained by the seal. It may be a solid, a liquid, a gas, a vapor or a mixture of all. (The term “medium” - is often used with interchangeably).
The chemical effect of the fluid on the seal is of prime importance. The fluid must not alter the operational characteristics or reduce the life expectancy of the seal significantly. Excessive chemical deterioration of the seal must be avoided. It is easy, however, to be misled on this point. A significant amount of volume shrinkage usually results in premature leakage of any O-ring seal, whether static or dynamic. On the other hand, a compound that swells excessively in a fluid, or develops a large increase or decrease in hardness, tensile strength, or elongation, will often continue to serve well for a long time as a static seal in spite of such undesirable conditions.
The Fluid Compatibility Guide and mobile site provide compatibility ratings for over two thousand fluids. The mobile site lists all elastomers with performance ratings of 1 or 2. For a static seal application, a "2" rating is usually acceptable but it should, in all cases, be tested. Where a "2" rated compound must be used, do not expect to re-use it after disassembly. It may have degraded enough that it cannot safely be reinstalled.