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High Vacuum:
High vacuum causes elastomeric compounds to lose weight through "outgassing" of absorbed gases, evaporation or sublimation of volatile components, and-in some cases-'produces a chemical change with an adverse effect on physical properties. Weight losses of up to 10% have been noted, depending on temperature, closeness to perfect vacuum, and the amount of volatiles (principally water) in the Compound.
Static face-type seals should be given more than normal squeeze to offset this weight loss. O-Rings should not be used for moving seals in vacuum applications. Fluorocarbon and Butyl materials have been successfully used for hard vacuum appliance.
Explosive Decompression:
All elastomeric compounds allow gases to diffuse into and to be absorbed and fill the voids in elastomeric materials. When high pressures are released suddenly, the gas expands inside the Compound. This blows up the rubber like a sponge, forms blisters on the outside surface, and even may blow off small chunks of the material. As the pressure inside the material returns to normal, the a-Ring returns to it original size.
This phenomenon is extremely bad at pressures over 1000 psi. Generally, there is no problem up to 250 psi. The only answer is gradual release of high pressures, or the use of special compounds which show the best resistance to this phenomenon. Usually, hard compounds in the 80 to 95 Durometer range show the best resistance to explosive decompression. 90 Durometer nitrile, and 90 Durometer fluorocarbon have exhibited good resistance in such applications.
Oxygen Service:
Althbugh many elastomers are compatible with oxygen, many applications may require non-standard compatibility ratings such as imparting no taste or odor to breathing apparatus, FDA, flash resistance (flame resistance) as well as permeation resistance. For such requirements, the user must note the special requirements.
Elastomeric materials are particularly combustible in the presence of pure oxygen. Sparks have been known to cause explosions.
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