I'm trying to find a % of air that will be or can be considered normal for mineral based hydraulic oil and also for water/glycol. At one time I had some data from some older hydraulic books but can't seem to find them now. Thanks, Tom

I really can't say if there is an actual "Normal" per cent of water content in hydraulic oils and water-glycol products (I assume you are referring to fire resistant fluids)
As you can see from this article
http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-2-1424/c-4.pdf
Many factors determine the actual determental effects of entrained water. SOme products seem to be able to handle to a greater or lesser degree entrained water before a problem occurs.
It would seem that if it foams, you have a problem. WHen a particular product foams is another matter based on many factors.
So the percent would vary also with regard to detremental effects.
Perhaps other board members could expand on this.
Hope this helps

Hawk

Thanks Hawk for your reply but I am looking for the amount of entrained air not water. From other info sources it seems to vay from a low of 6% to a high of 12%-just looking for other input. Tom

go to page 4.3 paragraph c on the link

Thanks again-basically the same article was posted on another forum on the web. My old Parker book gives 9% air if my memory serves me correctly. I'm in a steel mill and most all our application are water/glycol-sampling is done every month and water content is maintained about 40%. Tom

You know, rereading my previous post, I did refer to water. I think I need a vacation! you were asking about air. My refered article had the air info, but I said water. Woof!