Back-up rings have no intended sealing function. Instead, as their name indicates, they are protective and supporting elements made from extrusion-resistant materials which generally have a rectangular cross-section. They are installed in a groove together with an elastomer sealing element, preferably with a corresponding O-ring in static applications.
McMurtry Spéirling defies gravity using fan downforce
Ground effect fans were banned from competitive motorsport from the end of the 1978 season following the introduction of Gordon Murray's Brabham...