Back Up Rings

Back Up Rings

Back-up rings, or anti-extrusion rings, are thin rings that are designed to prevent O-ring extrusion under pressure. They fit in the gland between the seal and the clearance gaps to provide zero clearance. Back-up rings provide added resistance support to a seal and minimise the risk of extruding a seal in its housing when under pressure. Back-up rings, sometimes known as anti-extrusion rings, are not designed to have any sealing function in their own right. They are there to support the actual sealing elements of a design and stop them extruding under higher pressures, or where metalwork clearances are larger than is ideal.

They can come in the form of a solid ring, a split ring or even a spiral ring, depending on the environment and for ease of fitting. Back-up rings are placed behind the seal in a single acting system, or on both sides in a double acting system. They are always made of a harder material than the seal itself to minimise extrusion in the sealing gap.

Consideration must always be given to the environment expected for the seal and its back-up rings. It is also important to consider acceptable friction losses in order to provide the most suitable solution.

Types