Lowering friction increases seal life
by reducing wear, increasing extrusion resistance, decreasing
compression set and the rate of chemical attack.
Breakaway friction must be overcome
for movement to begin. It is influenced by the duration
in which an application remains stationary. The longer
the duration, the more lubrication will be forced out
from between the seal and the contacting surface. The
seal material then conforms to the profile of the surface
finish. These events increase breakaway friction.
Stick-slip is characterized by distinct stop-start
movement of the cylinder, and may be so rapid that it
resembles severe vibration, high pitched noise or chatter.
Seals are often thought to be the source of the stick-slip,
but other components or hardware can create this issue.
Causes of stick-slip include
swelling of wear rings or back-up rings, extreme side-loading,
valve pulsation, poor fluid lubricity, external sliding
surfaces or seal pressure trapping. This condition can
be puzzling or difficult to resolve. Possible causes
and troubleshooting solutions are listed in the following
Table 2-2.
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