An O-ring’s primary function is to restrict the movement of fluid or gas, such as prevention of fluid from leaking from a location, or prevention of fluid communication between locations, or sealing in general.
In some applications, O-rings also play roles in electrical insulation. A simple test is set up to study the electrical resistance across an O-ring seal in a conductive fluid environment: O-rings were positioned underneath a PEEK press-head and squeezed into the bottom of a smooth glass basin. The PEEK press-head had a hole in the bottom to allow it to be filled with water simultaneously with the glass basin.