The evolution of labyrinth seals into bearing isolators.
Bearings have been used for a long time in one form or another. Some of the earliest recovered examples of a rolling element bearing are over 2000 years old. Early bearings were often made of wood and lubricated with animal fat.
The dawn of the Industrial Revolution both created a need for higher quality and more capable bearings and provided the materials needed to produce these bearings in large quantities. However, the bearing alone does not operate well without reliable lubrication, and that lubrication does not perform well if it is contaminated, leading to premature bearing failure. This necessitated the addition of some form of seal to the bearing assembly to keep the contaminants out and lubrication in.
Many solutions can be applied to this problem;
- Felt rings. This is a low cost solution, similar in concept to pump packing, though it is good at keeping solids out of the bearing, it has little to no ability to keep moisture out of the lubricant, even a very small amount of water can have a dramatic effect on the performance of the oil.
- Lip seals. These are very effective at keeping solids and liquids out of bearing oil or grease. However, they are a wearing component, requiring replacement after around 3000 hours of operation, depending on the material and lip seal design. This type of seal can also leave wear on the equipment shaft, requiring extensive parts replacement over time.
- Labyrinth seals. This type of seal creates a difficult path through to the bearing. This, coupled with the rotary motion of the inner part of the labyrinth and drainage ports at the base of the unit, allows for good resistance to solids and liquids ingress. This design is also non-wearing, so equipment damage is eliminated.
- Magnetically energized seals. Though these seals can be effective, their relative size and increased cost tend to limit their use to applications with significant problems.
Of the four options listed above, labyrinth seals have emerged as the preferred choice in most applications. The design and implementation of Labyrinth seals has evolved to meet increasing demands of equipment reliability, safety and performance.
Early Labyrinth designs.
The early labyrinth designs we generally two piece designs, consisting of a rotary element affixed to the equipment shaft and then a corresponding ‘negative’ of the rotary element normally machined into the equipment housing itself. This design can still be seen in a lot of equipment and in certain environments can prove to be effective, though they are less effective in environments with higher moisture content or high particulate counts.
The modern Labyrinth seal.
For several revisions, API 610 has stated that a labyrinth style this bearing seal or isolator is the recommended standard for bearing housings. The design of Labyrinth seals has improved over time by incorporating other elements of fluid sealing to broaden the range of applications to which it is well suited. Modern isolator designs can be IP (ingress protection) rated to 66 or higher with some additional features. Several Labyrinth designs now include O-rings intended to provide a positive seal even when the equipment is stationary.
The modern Labyrinth seal is also now supplied as an assembled unit intended to be installed into the equipment. The nature of this assembly allows for the use of advanced static sealing techniques without the risk of wear to the equipment that it is installed into.
These advanced features however can increase the cost of the Labyrinth seal significantly. To help offset this potential issue, many manufacturers designs allow the labyrinth or isolator to be rebuilt using minimal parts (typically just a few O-rings). When considering repairable labyrinth seals it’s important to understand if any specialized tooling or components are required to facilitate the repair. Some manufacturers utilize custom elastomer grades or require special tooling for each size of isolator or labyrinth which can inflate the cost and add complexity to the repair process. If you are considering a repairable design, look for one that only uses standard O-rings and does not require special tooling to facilitate the repair. Using standard O-ring sizes means that its easier and less expensive to repair the labyrinth and also means you are less likely to be stuck waiting for parts in a rush situation.
The advanced QXE bearing isolation range from A.R. Thomson Group Inc. Fits this role perfectly. Contact us today to see what we can do for your plant uptime!