Effects of a Surface Engineered Metallic Coating on Elastomeric Valve Stem Seal Leakage Page: 20
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the elastomer. The lubrication film also helps control chemical reactions at the boundary
layer between the elastomer and metal. These chemical reactions can result in the
formation of particles that damage the surfaces and limit seal ability (Martini 1984).
Breakout friction is the other type of friction that occurs in O-ring seals. Breakout
friction occurs after the seal has been at rest and first starts to move. This friction is a
function of how long the seal has been at rest and is usually much higher that running
friction. It is believed that this is due to the elastomer flowing over time into the voids
and crevices in the surface of the metal (Parker Hannifin 1999). Also, lubrication tends
to be squeezed out during periods of rest so there is very little lubrication initially (H6rl
and Haas 1997). Lubrication has not been as effective in reducing this friction (Parker
Hannifin 1999).
O-ring lubrication is also important in pneumatic seals. When a seal is used for
liquid service, the process medium provides some lubrication. In the case of gas service
there is less inherent lubrication from the process fluid so the initial lubrication of the O-
ring becomes more critical. Besides the reduction in friction, lubrication can reduce the
leakage of a gas through the O-Ring.20
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Taylor, John Abner. Effects of a Surface Engineered Metallic Coating on Elastomeric Valve Stem Seal Leakage, thesis, December 2000; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc2690/m1/28/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .