Back-Up Rings

Back-up Rings are parts fitted together with an O-Ring. They do not properly have a sealing function but are rather dedicated to improving the performance of said O-Ring. Depending on the application and the housing, one or two BUR can be fitted around the OR allowing its use in static or dynamic systems, in reciprocating or rotating movements and achieving the use of a wide range of OR hardnesses.

Its profile is pretty basic since its most simple version is a rectangular section washer. However, the most standard profile is the concave cross-section washer that allows the O-Ring to be seated, improving the anti-extrusion effect.

The standard material that we usually stock is NBR90 although it can also be manufactured in FPM, PTFE, POM, PU,… on request.

Another very efficient profile in reciprocating applications is the spiral BUR made of virgin PTFE. These are two spiral windings cut at an angle at the end that can be fitted with an FPM OR when the working temperature requires it. Finally, we can highlight that BUR can be cut with different angles, which allows their assembly in closed housings.

To facilitate their identification, although obviously both the concave section rings in NBR90 and the spiral PTFE rings have very standard sizes in their respective ranges, the BS number of the AS-568 range is usually the easiest way to tie in a BUR with an OR. For example, instead of ordering a BUR which sizes are 32.16 × 3.00 × 1.00 / 1.27, it is easier to refer to the BUR218 as it will be fitted with a BS218 O-Ring (31,34×3.53).