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Air Entrainment Worries

D dgeesamanMember
Hello everyone.

I am designing a modification for a gear drive that converts the lower bearings from immersed lubrication to waterfall lube with a reservoir below. I would like your opinion on:
1) whether the bearings will churn the oil and entrap substantial air
2) how I can design the reservoir to release entrained air and avoid excessive foaming

Here's the scheme:
The oil will first fall thru a spherical roller bearing and then thru a spherical taper roller thrust bearing. 13" shaft, about 400rpm, using a high viscosity synthetic gear lube with some anti-foaming additives. My current reservoir design has a dwell time of 2 minutes, 5" oil level, and about 5" of room before it bubbles over.

Naturally I'm concerned that one or both of these bearings will create a lot of entrained air, and whether that will cause lubrication or pump problems. Also foaming could cause my reservoir to bubble over.

Thanks
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J johnmMember
No design cannot be completed or validated without building and running a prototype. Observations during the runs are invaluable to a designer in efforts to correct “events” and change design accordingly. Theoretical conclusions are OK, but have limited impact on the desired performance of the prototype and the final product. I suggest you build a prototype, and have fun with it. In the process, you will reach conclusions you never anticipated before. There is nothing even close as effective as is getting your hands on it and tweak it and test it. Please don’t find my comments as an attempt to discourage you on any way, but rather as encouragement in your design work. I just aired what I have learned in my “design” attempts.
D dgeesamanMember
Thanks John.

Unfortunately, this design change is a retrofit on an existing setup in the field, so a prototype is less feasible than most situations. I think we'll end up spending extra attention during the first installation and startup. If there are issues we'll need to resolve them very quickly.

If you have any ideas what 'bag of tricks' work for releasing entrapped air, it would help me immensely.

Dave
V vsdaveLevel 3 - 101 to 250 posts
What is the pump flow capacity ? Do you have any idea about the air releasing time for the type of the oil being used by you ? You can get the details from Oil suplier. Normally for Hydraulic air releasing time is 4 minutes. For the type of the oil used by you it may be more. In that case pump flow capacity becomes important looking to the dwelve time. If you are reftrofitting the machine extra Oil volume should solve your problem. May be dwelve time can be increased to 5 Mints !!!

V.S.Dave.
quote:
Originally posted by dgeesaman:
Hello everyone.

I am designing a modification for a gear drive that converts the lower bearings from immersed lubrication to waterfall lube with a reservoir below. I would like your opinion on:
1) whether the bearings will churn the oil and entrap substantial air
2) how I can design the reservoir to release entrained air and avoid excessive foaming

Here's the scheme:
The oil will first fall thru a spherical roller bearing and then thru a spherical taper roller thrust bearing. 13" shaft, about 400rpm, using a high viscosity synthetic gear lube with some anti-foaming additives. My current reservoir design has a dwell time of 2 minutes, 5" oil level, and about 5" of room before it bubbles over.

Naturally I'm concerned that one or both of these bearings will create a lot of entrained air, and whether that will cause lubrication or pump problems. Also foaming could cause my reservoir to bubble over.

Thanks
J johnmMember
dgeesaman:
This link http://scholar.google.com/scholar?q=air+entrainment+in+...n&lr=&start=10&sa=N, is full of "food for thoughts", where folks displayed their articles and patents regarding cutting down on air entertainment in gear oils. By reading them you might get some idea that would benefit you.
More conventional way would be to hook up an off-line filter, as we all know that particles serve as seeds for air entrainment (less particles – less air entertainment in oil). Filter should have an air release valve on its housing. Oil and air would be separated in the filter, and airless oil would be returned to sump. In such setting you may look into expanding your gear sump. Oil temp also is a factor and could be monkied around with (hotter oil – thinner oil – greater air release rate). Of course, increasing oil temp has its limitations that should be considered.
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