Water Vapor in Bearing Cavity
Water Vapor in Bearing Cavity
(OP)
When specifying seals for bearings, I have come across these claims.
When bearings start, they increase temperature, resulting in a build up of pressure in the bearing chamber. This is usually expelled through the vent, or through the seal. When bearings stop, the heat dissipates, resulting in the bearing chamber sucking air through the seal. This air has water vapor in it, which then enters the lubrication, and reduces bearing life.
Has anyone in the bearing industry seen this phenomenon? Is the small amount of vapor really affecting the lubrication system / bearing? How much would a contact seal really increase bearing life opposed to a non-contact seal, provided the only difference is this start-up / stop water vapor issue?
Any help would be appreciated.
Thank you.
When bearings start, they increase temperature, resulting in a build up of pressure in the bearing chamber. This is usually expelled through the vent, or through the seal. When bearings stop, the heat dissipates, resulting in the bearing chamber sucking air through the seal. This air has water vapor in it, which then enters the lubrication, and reduces bearing life.
Has anyone in the bearing industry seen this phenomenon? Is the small amount of vapor really affecting the lubrication system / bearing? How much would a contact seal really increase bearing life opposed to a non-contact seal, provided the only difference is this start-up / stop water vapor issue?
Any help would be appreciated.
Thank you.





RE: Water Vapor in Bearing Cavity
Certainly I have seen levels higher than that in the oil although the cause is not exactly clear.
We have had problems with moisture intrusion causing bearing rust on machines which sit idle for long periods of time. I have not heard of it for machines with frequent start/stop. I personally would be most interested in the ability of the seal to prevent breathing during secured operation.
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RE: Water Vapor in Bearing Cavity
the same. It pays to run them periodically
to ensure lube is on all surfaces. I think
the water condensates and this is the worry
especially near the top surfaces. Even grease
lubed bearings need to be rotated periodically
to ensure grease is distributed evenly around
the bearing surfaces.
RE: Water Vapor in Bearing Cavity
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RE: Water Vapor in Bearing Cavity
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RE: Water Vapor in Bearing Cavity
It created problems on start-up unless maintenance people were trained to take the caps off the bearings housings and check for water content just before startup.
Corrosion on the raceways of the spherical roller bearings was evident leading to early failure on start-up.
We solved the problem by changing the grease to a calcium-sulphonate based product (made by FINA at the time, now TotalFinaElf). It was far more 'water tolerant' than standard Lithium or Lithium-Calcium EP2 bearing greases.
Rotating the machinery during a long term shut down might not be practical, and if you have a lot of water you'll only emulsify what you have there anyway. But it is still a good practice for motors, pumps etc in storage.
Lester Milton
Telford, Shropshire, UK
RE: Water Vapor in Bearing Cavity
RE: Water Vapor in Bearing Cavity
Has anyone tried to use these to seal out this water vapor?
Thanks.
RE: Water Vapor in Bearing Cavity
Lester Milton
Telford, Shropshire, UK
RE: Water Vapor in Bearing Cavity
We have a science instrument that uses two angular contact ball bearings seperated by polymide bearing retainers. The polymide bearing retainers functions as a lubricant reservoir. The lubricant used is Apiezon C oil.
The science instrument will be in storage for about 7 years. Following things come to my mind.
1. Lubricant loss due to vapor pressure in 7 years
2. Instrument may require a drive test once in a year (I do not know the frequency) to make sure the bearings etc. work properly.
3. Degradation of lubricant in 7 years.
Can anyone add to this from your experience? What I have missed to account for? What would be the frequency for item 2?
Thanks in advance for your help.
Regards,
- Dipak
RE: Water Vapor in Bearing Cavity
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RE: Water Vapor in Bearing Cavity