Lip Seal Damage 1

[TugboatEng]

I am looking for some insight into the cause of damage of these lip seals. I believe the material is FKM, shaft speeds are variable but can reach 600 feet per minute. Pressures are not more than a few feet H2O. Temperature ranges from ambient to not more than 150F. The fluid is gear oil or an emulsion of oil and water. The seals are providing satisfactory service but are severely damaged at the end of their expected life. The first picture is after 4 years in service and the second is 1 year.

 

[romke]

the reason might be the lubricant with which the seal is in contact. for automotive applications modern gear and engine oils are formulated in such a way that seals will swell just a little and that they do not become brittle and only lose a little of the original hardness. in automatic transmission oils a rubber swell agent is added to promote the preferred changes in use, in engine oils the character of the base oils used normally is such that no additive to that effect is required. both transmission oils and engine oils do however need to pass certain test requirements. usually those tests are immersion tests for a certain amount of time, after the test hardness, brittleness and size are measured and need to be within certain limits.

immersion tests are usually not required to meet industrial gear oil specifications.

 

[TugboatEng]

There are 4 other identical seals in the housing but it's only the ones exposed to water that are showing the damage. I don't know if it's clear in the picture but the damage consists of craters at almost uniform spacing along the centerline of where the lip contacts the shaft.

 

[btrueblood]

Sounds like, and looks like cavitation damage.

 

[TugboatEng]

Reading this

https://pure.tue.nl/ws/files/4352687/605744.pdf

about lip seal cavitation indicates that it prefers the edges of the contact area and we're seeing damage straight through the center. Rubber also seems to be more tolerant of cavitation than metal and we're not seeing any unusual wear of the metal shaft sleeves.

 

[acspain]

Water and rotating shaft seals don't mix. Water has very little lubricity to reduce lip seal wear. The seal is probably sticking to the shaft where water precludes the oil and pieces are being torn out when the shaft rotates.