If flange and enclosure door surfaces were perfectly smooth and perfectly aligned, gaskets wouldn’t be needed. In the real world though, uneven gaps are always present and must be sealed to prevent leaks or contamination. Sealing options range from inexpensive red rubber and buna N materials to advanced silicone rubber gaskets, and include materials as diverse as graphite, PTFE and paper.
When replacing gaskets it’s common to use the same material that’s just been removed. If joints never change, that approach is often adequate. But by considering the nature and design of the sealing surfaces or flanges, it may be possible to select a longer-lasting material.
Impact of flange material
Some flanges can’t take high clamping forces, especially as they age. Plastics tend to become brittle and some metals lose ductility as they age, particularly if put through repeated temperature cycles. This means a soft, easily compressed gasket material is needed.
Impact of flange geometry
Bolt patterns or the position of clamps and latches can distort the mating surfaces, leading to uneven gaps. For example, an enclosure door with a single central latch can leave large gaps at the corners when closed. Also, a flange that’s been assembled and dissembled repeatedly for many years will start to distort, creating uneven gaps.
Flange alignment can change over time. After years of service it’s possible that piping will have moved, with the result that flange faces are no longer parallel. Again, the result is an uneven gap. Another problem is surface imperfections resulting from careless gasket removal.
These problems demand thicker gasket material that provides more compression. But thicker material needs higher loads to compress down in the joint, and those loads can lead to more distortion in the flanges.
Flanges and mating surfaces change over time and products that performed well, perhaps red rubber or buna N gaskets, may no longer be up to the job. When replacing gaskets, consider the condition of the sealing surfaces or flanges. A different material may last longer in the joint.