Greetings. I stumbled upon this forum and it seems like there are some skilled people here!

I am commissioning a prototype 50 MW motor/generator and I am fighting oil aeration with my SHC 624 (ISO VG32) bearing oil. I have a well baffled tank and I am augmenting its capabilities further; my question is more about these two lubes.

Although the 624 advertizes good air release properties the DTE Light series (also ISO VG32) actually advertizes an ASTM test to support its claim.

Anyone have any experience with either of these that you could please comment on? If/when I try it out is mixing (~ 1 gallon out of 80) an issue?

Many thanks .............

Just my observations with no scientific testing to back it up but. I feel that Mobil SHC 600 series oils do keep air entrained longer than similar oils. I have had the same problems in gearboxes causing foaming in the sight glasses.

If you want to do your own rough foaming tendency test it is not difficult. Put each sample in a sample jar 1/2 full. Shake them up at the same time. See which one takes longer to separate. Or pay a lab to give you a more formal result.

Sorry, I don't know the answer to your question.

I do not think hand shaking a sample would be a rigorous enough agitation the give a real approximation. Using a blender, paint shaker, or even a hand mixer would give a better idea of how well the oil sheds very fine air bubbles.

About air mixing .........

We have internal gear pumps evacuating the bearing sumps. Naturally they have more capability than the oil coming to them so they 'gulp' air in with the oil. Not so bad there. But when this goes through the gears the air is thoroughly 'blended' together with the oil much like a household blender mixing milk or orange juice ...........

Have you considered using screw pumps? If you can, give it a try. Gear pumps are notorious for whipping air-oil or oil-water mixtures. Although many people know this, they still choose gear pumps, because they are much cheaper than screw pumps. I always thought it is the wrong way to save a buck....

When I see lots of bulbs in oil, my first assumption is always that the oil gets dirty. Especially during commissioning, the chance falls large.

Also in most cases, surface tension is the reason to form bulbs. Seveal drops of chemcial may eliminate bulbs. But reduce surface tension may cause emulsification problem. It's up to your choice.

Foaming is a relative and usually qualitative issue. First question, is the foam causing an issue with the mechanical equipment? If yes, then it needs to be addressed. Foam is a direct relationship to surface tension. Contamination, areation, water, etc can alter the surface tension of the oil and cause the air to not release and hence the foam.

Try cleaning the oil and making sure the system is clean. If you still have issues, try Mobil SHC 824 (ISO 32). This oil has demostrated less foaming issues. Foam test ASTM D 892 10/0 & air release is a 1. This is the normal Mobil recommendation for gas turbines.