How to choose the right o-ring size ?
One must distinguish two specific cases while choosing an o-ring.
- The o-ring has to be positioned in a gorge.
We recommend to measure the distance from the point where the new o-ring will be positioned. Indeed, an old joint is often slack and this can distort the real distance. It is essential to measure two distances : the torus diameter, and the inner diameter.
Cross-sectional diameter : you must measure the thickness of the groove.
Inner diameter : it is the inner diameter of the groove.
In case you have any doubt, it is better to take the smallest one : a new joint will always be able to expand a bit if you pull it.
- There is no groove in the joint's position : it is based on a flat area or on a bevel.
Cross-sectional diameter : you must refer to the existing joint and choose the same diameter, but a little bit thicker.
Inner diameter : you must refer to the existing joint, and choose the same diameter, or a smaller one .
It is worth mentioning that bigger is the joint, the more it will tend to expand over time. An o-ring greased with a silicone grease will have a better waterproofness, and its lifetime will be increased.