Feel free to ask questions or discuss any issues related to mechanical seal technology
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I’m happy to answer any questions regarding mechanical seals for free, so we can all improve together. :D
I would like to ask an expert: 1. Have you used the 3NC-FB method? Is it only applicable to media that vaporize easily? Does the first dry gas seal have an air supply? I’ve never seen it before. Why isn’t PTFE suitable as an auxiliary seal? Thank you
First, a dry gas seal without an air supply is like a car without fuel. Secondly, PTFE is not suitable as an auxiliary seal for dry gas seals, because dry gas requires a high level of stability; it’s similar to why Apple phones are not packaged in plastic bags.
1. 3 refers to pressurized double-end face, while FB denotes face-to-back configuration. Any medium that theoretically does not react with nitrogen will work. The first seal seems to be a wet seal, so no air supply is required. 2. The thermal expansion coefficient of PTFE is too high; in other words, the dimensions cannot be maintained after heating and cooling. So it is not suitable as an auxiliary seal. It’s just my personal opinion; I hope it can serve as a starting point for further discussion.
1,3NC—FB; the first one is obviously a dry gas seal. Otherwise, wouldn’t it just be 3CW? 2. I heard the same thing, but no professionals provided an explanation. I’m still very grateful.
I would like to ask the teacher: Is it necessary to apply lubricant to the sealing surfaces of the stationary and rotating rings in a mechanical seal? It still gets wiped very clean. Additionally, how is the compression amount of a single-spring mechanical seal determined, and how is the total compression amount measured during regular maintenance?
It is essential that the sealing surface be clean; it can be wiped with alcohol. Applying lubricant to the sealing surface is not a good practice. The compression amount of a single spring is subject to size specifications; if the installer is not aware of these specs, it’s fine to compress it to a little over half of its maximum compression amount. For example, if compressing a spring by 30 mm brings it to its maximum compression, then compressing it by 15–20 mm should generally pose no problems.
I’m ashamed to say that I have only been exposed to 2CW-CS, as well as the 72+75/76 regimen. Special media that can react very easily with hydrogen, oxygen, water molecules, and the like in the environment can also be considered, but cost must also be taken into account. The two sealing areas should share the same isolation gas source, following scheme 74, similar to 54. II. The use of PTFE as an auxiliary seal in traditional mechanical seals is quite common; for example, in Krane’s 59U and Cron’s C8BV models, it replaces materials that would otherwise require FFKM, offering a clear cost-performance advantage. These are just my personal opinions; please feel free to give your feedback!
Have you ever seen one that is sealed with one-way passage properties? Under negative pressure, air cannot leak into the medium side. Leakage occurs at positive pressure airtightness (negative pressure close to absolute vacuum, positive pressure 60 kPa)
I don’t think PTFE is unsuitable as an auxiliary seal ring; it’s probably only the case in dry gas seals of this type. We have used PTFE sealing rings at temperatures up to 120°C, and there were no issues. Its resilience is definitely inferior to that of other gasket materials.