known as gas expansion rupture or O-ring embolism, explosive
decompression is a major risk for any seal
operating in a high-pressure gas environment.
Gas can get trapped inside the seal’s micropores.
If the seal faces an equilibrium shift (as with
rapid decompression), this trapped gas rapidly
expands in an effort to match external pressure.
amount of structural damage done to the O-ring
as a result of this internal expansion depends
on the volume of the trapped gas and the hardness of
the seal. Smaller volumes (especially in soft compounds)
may only cause surface blisters which
can disappear as pressure equalizes. Larger volumes
(particularly in hard compounds) can cause deep cross-section ruptures
or even total O-ring disintegration. Higher temperatures
further aggravate this phenomenon. Figure
131 is an example of O-ring failure
due to explosive decompression.
way to prevent explosive decompression is to allow
for longer decompression periods. Trapped gas can
exit the elastomer more
slowly, minimizing the chances for damage. Use
of seal materials in excess of 80 Shore A may also
be helpful. Harder, high shear
modulus seals have the strength to dissipate
fracture energy as it propagates through the O-ring.
Smaller cross-sections offer less space in which
gas can become trapped.
speaking, carbon dioxide (CO2)
is more likely to cause elastomer swell and
rupture than nitrogen. For CO2 contact,
as in air guns, polyurethane is
by far the best choice. For seals facing nitrogen
and other pressurized gases, high-ACN
content nitrile may be a solution. In
some cases, you might consider soaking the seal
in specific oils (such as MIL-H-5606) prior to
use. The oil fills the spaces that might otherwise
be filled by gas.