Over 100 Years of Labyrinth Seals
When it comes to seals, labyrinth seals are a standard design choice, and engineers have researching and implementing them for over one hundred years. The purpose of this post it to present you with seven questions about polymer labyrinth seals that you should know the answers to.
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What Kind of Seal is a Labyrinth Seal?
A labyrinth seal is a type of dynamic mechanical clearance seal characterized by long life and low friction that is typically used to isolate areas of low pressure from areas of high pressure.
How Do Polymer Labyrinth Seals Work?
The word labyrinth usually brings to mind a maze full of complex, confusing passageways, which is an excellent description of how a labyrinth seal works.
Labyrinth seals make it difficult for liquids to make their way through the seal barrier because of a complicated set of paths that a liquid or contaminant has to maneuver through in order to overcome the seal barrier. In fact, one of the goals of these complicated pathways is to create areas of turbulence and flow friction that reduce the kinetic energy of the contaminants trying to get in. Because of this, they outperform regular seals in keeping contaminants out and liquids in. Regular seals can do an outstanding job of keeping liquids in, but do not perform so well in keeping contaminants out.
How do Lip Seals and Labyrinth Seals Compare?
Lip seals make contact with the shaft, and with time the lip will begin to wear off and the performance of the seal will be compromised. Labyrinth seals, on the other hand, do not actually contact the shaft and therefore do not experience the same kind of wear.
What are the Benefits of Polymer Labyrinth Seals?
Benefits of polymer labyrinth seals over lip seals include efficiency, ease of installation, and excellent reliability. Reliability is due to several factors: corrosion resistance, gall resistance, and the fact that they can maintain clearance during occasional rubs, unlike lip seals.
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What are the Disadvantages of Polymer Labyrinth Seals?
The disadvantage of polymer labyrinth seals compared to regular seals is cost: labyrinth seals are more expensive, and may require that the equipment be retrofitted. However, they do last much longer than normal seals and therefore do not incur as much financial loss due to downtime, replacement seals, and costly (and possible catastrophic) failures.
What Kind of Polymers are Typically Used in Labyrinth Seals?
Polymers have been used for labyrinth seals for over twenty years now. Two of the most common polymers used with Labyrinth seals are the thermoplastics PEEK (polyetheretherketone) and Torlon PAI (polyamide-imide). Other polymers include Vespel PI (polyimide) and Flourosint (enhanced PTFE).
Where are Polymer Labyrinth Seals Used?
Polymer labyrinth seals are excellent for use in heavy wash down areas (for example, where they may experience repeatedly splashing with water) or areas where airborne particulates are high. More specifically, they are used in cryogenic rocket turbopumps, primary and secondary airflow in gas turbine engines, rolling element bearings, machine spindles. It is noteworthy that NASA considers labyrinth steals to be the most common choice in flow-path seals in the history of turbine engines.
Conclusion
Polymer labyrinth seals are mechanical non-contact dynamic seals that use a maze-like structure to prevent the ingress of contaminants and reduce the egress of the media they are sealing in. These mechanical seals are popular for a variety of reasons, including lack of wear, reliability, and ease of installation. They are used in many applications where there is a need to separate a low pressure area from a high pressure area, from rocket turbopumps to machine spindles. The initial cost of labyrinth seals may be more, but they save money over long haul with their outstanding reliability. So, the next time you are looking for a mechanical seal that needs to outperform the others, check to see if a polymer labyrinth seal might meet your needs!
Check out our free Polymer Sealing Troubleshooting Guide!
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