How to estimate the friction an O-ring will develop?

The best way to determine running friction is during trial-runs because application factors can change the running friction. Friction, either break-out, running, or both, can become troublesome in some applications. Surfaces deformation of O-ring piston or shaft seals can result in friction as well. In addition to the usual causes of friction, such as the hardness of the rubber, the type of surface, the surface finish, the squeeze on the O-ring, the amount and type of Iubrication, the fluid pressure, and the temperature, the amount of break-out friction which an O-ring will develop depends on the length of time the surfaces of the metal and the rubber have been in contact.