Hydro Generators

Good Day,
The oil could be anywhere between an ISO 22 and an ISO 68 but it depends on the design and specifics of the application. I am going to assume that you are considering an oil cooler to minimise the circulating oil's temperature and hence give a similar viscosity across the changing temperature variations. One thing to remember is that the flow was origionally determined by the oils ability to adheer to the ring and this was in part a function of the tackiness or adhesion or surface plating charastics of the oil. These functions are partially independant of ISO viscosity. Also the oil rings supplied the minimum amount of oil required. As long as the oil doesn't cause an imbalance or an oil whirl or oil whip situation you can't put too much oil into the bearing by simple splash methoid. So the more you put in the easier it would be to remove the heat. etc.
Your best bet is still to contact the OEM who has a better understanding of the specific system than the rest of us. Chances are they might have a retro-fit system to sell you. Or they would assist you in designing a system, their reputation is also at risk here.

hope this helps...

The flow and temperature in the application you mention is very much dependent on the foaming caracteristics of the oil being used. I just reduced the bearing temperature in a similar gererator 20 degrees C. by changing out the cheap group I turbine oil and using a high quality group II product.

Do you intend to keep the oil ring or install an nozzle at the top of the bearing to get the oil inside the bearing. I would see no reason to change the viscosity from what you are currently using unless you expect a significant drop in operating temperature. The advantage of a circulating system is the ability to cool the oil and remove contaminants using an inline filter. Which improve long term life and reliability

Prior to insatlling the lubricating systems we were using Mobil DTE 26 an ISO 68 oil. Our Mobil Lubrication Engineer and the distributor's representative recommended using an Mobil SHC 629 an ISO 150 PAO oil. After installing the lube system we have had some drainage problems, possibly due to the cool temperatures. I believe if we get the flows right we can remove the rings using the nozzle feeds. The main concern is to ensure we have enough oil feeding the bearing and not have drainage problems. Presently most the flows are on .6 litres/min. and the thrust bearings are at 1.2 litres/min. Also these are very old units which have had many upgrades over the years. GE has been unable to supply the needed information to this point.