What is Stiction? 

Stiction is the resistance to the start of motion usually measured as the difference between the external force being applied in order to overcome the static friction and the force to maintain movement between the two contacting or working surfaces.

It can result from: corrosion, cold welding, breakdown of lubrication, build-up of deposits, chemical reactions, breakdown of the sealing components…

Many studies and organizations have defined stiction, in different ways.  Yet, all agree that stiction is the act of being “stuck” by static friction which prevents one surface from moving against another.  Further, if the external force becomes greater than the static friction, the stiction between two surfaces will be overcome and the object will begin to move again.

Stiction research shows other failure modes become significant when these products do not move frequently – some failure modes become significant if a product is static (motionless) for 100 hours. When O-rings and other seals are part of a product, many failure modes become significant when the product remains static for a week or more, for most of these failures are dangerous.  Improvements in safety and reliability can be obtained with stroke testing or even partial valve stroke testing, for once the stiction is broken via movement the friction build begins over.