how to increase viscosity loss in high VI hydraulic oil in short service due to shear of VM?
Original Post
Read our primer articles on Oil Analysis and Tribology
Replies sorted oldest to newest
I haven't had to do anything like that.
But it sounds like you are looking for something you can add to oil to restore its viscocity.
Be careful!
And look with a critical eye at your entire data set for the cause. Is it heat? or simple shear?
Are you using the correct oil for the conditions? The OEMs spoec oils based on a set of operating and environmental conditions. If you are exceeding those and using there base recommended oil, it can lead to trouble.
Don't go blindly off changing stuff. Tell us more and let us help.
But it sounds like you are looking for something you can add to oil to restore its viscocity.
Be careful!
And look with a critical eye at your entire data set for the cause. Is it heat? or simple shear?
Are you using the correct oil for the conditions? The OEMs spoec oils based on a set of operating and environmental conditions. If you are exceeding those and using there base recommended oil, it can lead to trouble.
Don't go blindly off changing stuff. Tell us more and let us help.
we used straight mineral and changed to high VI hydraulic oil and experience viscosity loss (40 degC)from 46 to 39cSt in short order.
A straight oil didn't change visc?
You change to a hi VI oil and visc decreased.
Why did you change, were you trying to fix something?
You change to a hi VI oil and visc decreased.
Why did you change, were you trying to fix something?
Intend to extend the oil hrs but apparently not a good idea in this case. Is the vis loss (46 to 39cSt)normal in high VI hydraulic fluid? What should I do next? Thanks
What visc values did you see with your straight oil?
What was the oil?
Whast is the new oil?
What was the oil?
Whast is the new oil?
This is possibly shearing of the polymer in the high VI oil due to it's application. What are you using the high VI oil in - application, speed, temp etc.
Oil companies make a range of high VI oils - some polymers are more shear resistant than others - I'd suggest you speak to your oil supplier.
Oil companies make a range of high VI oils - some polymers are more shear resistant than others - I'd suggest you speak to your oil supplier.
It depends on the base stoke quality also.Are you using Gr-I oils.Pls confirm it with the oil manufacturer.GR - II and above is beeter to resist such types of shearing and viscosity loss....
I'm not ready to jump on the shear-stability bandwagon just yet.
You mention the "upgraded" product is "high VI". There are lots of ways to get an increase in VI. The most common is to convert to a PAO-based fluid. PAOs have naturally high VI. As such they need less VI improver and should be much more shear stable. You could also use mineral with added VI improver. (Most mineral hydraulics don't contain VII.) In that case, shear stability can be an issue.
Are you certain you are seeing a change in VI? You only quote the viscosity change at 40C. If the problem related to VII, you would see some atypical response in the 100C as well.
What other maintenance was performed when you made the conversion? Was there a flush? If so, what did you flush with and what was its viscosity? It may be a contamination issue, either a one-time event because low-vis flushing medium wasn't all drained from the system, or ongoing because of something got mis-connected during the outage when the conversion was made.
You mention the "upgraded" product is "high VI". There are lots of ways to get an increase in VI. The most common is to convert to a PAO-based fluid. PAOs have naturally high VI. As such they need less VI improver and should be much more shear stable. You could also use mineral with added VI improver. (Most mineral hydraulics don't contain VII.) In that case, shear stability can be an issue.
Are you certain you are seeing a change in VI? You only quote the viscosity change at 40C. If the problem related to VII, you would see some atypical response in the 100C as well.
What other maintenance was performed when you made the conversion? Was there a flush? If so, what did you flush with and what was its viscosity? It may be a contamination issue, either a one-time event because low-vis flushing medium wasn't all drained from the system, or ongoing because of something got mis-connected during the outage when the conversion was made.
