I have been fighting a varnishing problem with one and really all of our Atlas Copco rotary screw air compressors. I was getting high ISO readings in the 4 to 10 micron spectrum, as you can see in the image I uploaded. The Atlas Copco service thought I was nuts as did a private company that fixes them and is kind of a partner with Atlas Copco smaller units that I consulted in my area. I was wanting to filter with better OEM filters or even some high end Donaldson filters but zero info was or really could be given to me by Atlas for what I assume are political reasons and lack of never testing Donaldson filters for approval to work in severe case scenario. I just knew something is wrong here and I went through 3 different oils, Schaeffer's that couldn't handle the heat and broke down with some surface gelling on an older unit I tested it on and was told later by the smaller firm it varnishes right up, pull it. Pulled that before I got his info because of the outcome that was obvious.
I got ZERO help from Atlas Copco and the small private tier company on this. I found a seeping bearing cap on top of the motor when just out of warranty and was going to start to use the small company and asked them to repair it because at the time I thought I was getting air pulled in from somewhere or some kind of micro-dieseling. They completely ignored me, I then went to Atlas Copco and wanted them to fix it and they completely ignored me, even after giving PO's too fix it. No, help saying to me hey ___ this happens on all of them really you don't need to fix this we see this all the time. They both thought I was a nut job. I have one of the highest credited labs in the country with 2 MPC test stating I have a major varnishing problem. And I am ignored!! Granted I was on a learning curve but as having an ex-hobby Audi repair business I am very mechanically inclined and I am the maintenance guy at our 100 person plant. All they wanted me was to "run the shmit out of it" and ignore the problem. The problem of just not a rotary screw unit, but also a variable speed motor that gets cooled by this oil that is filled with varnish basically shot peening the bearings with this micro-fine varnish particles. The varnish is not as degrading to the bearings as wear metals, long term circulation of ultra high values will kill those bearing early. So who gets to pay for the new $8,000 assembly when it goes down early in life from dirty oil and bearing wear/heat issues. Certainly not them? My company will, and they will make the profit. I even got a Noria Corporation free 30 min consultation and 2 paragraph comment that after studying my 12 at the time analysis tests my unit is destined for a very early failure. They stated this problem needs to be dealt with ASAP.
Then I went to Summit Industrial oil earlier on in this process, a Kluber company. I was told their SH-46 would work a PAO with some Ester. That didn't work either, as far as my testing. I ran two different MPC varnish tests that proved I had an issue going on. Atlas ignored my findings as did Summit because they thought I "had too much information" overload. That all just said run the SH-46 and when you hit a certain acid level from our free lab testing change it out. They discounted my MPC tests "because we don't look at that test" I got from them,"run the [censored] out of it." Even though they have a better oil, Summit Ultima, a group 5 Ester based (POE) for $50 more per 5 gallon. He didn't think I needed that. No you don't need that our SH-46 is more then enough. "Just run the [censored] out of it."
Well, I did another cleaning with Summit Vanasolv in this problematic Atlas and used Summit Ultima. It appears to be the ticket to fixing what I can only suspect is a hot spot or hot spotting some where in the unit. Notice the Unit hour time and the oil hour time.
Test #9 and #10 is Atlas Copco Roto-Xtend OEM (PAO)
Test #11 and #12 is Summit SH-46 (PAO with some Ester)
Test #13 and #14 is Summit Ultima (POE)