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Varnish could be the problem. When oil oxidizes it will form varnish build-up on the internal metal surfaces and form an insulation barrier. If your system has a heat exchanger then varnish will build up on the metal surfaces and not allow the cooling process to work, and cause high temps.

Check out our website and let me know if you would like us to perform a FREE varnish test on your oil.

Paul Jarvis
interesting - trip on high coupling's lube oil temp. this type of protection scheme is new to me. i can only think that the TE is best placed at the coupling oil return line. am i right?

what is the oil temp difference like between running the comp at normal or high load to low load conditions? any change in vib as the temp increases? i would do the followings ;

1) oil analysis - believe you have done this and you see no abnormality.even if there is abnormality, i dont think you can conclude the issue from there
2) if there is rise in 1X while offloading the comp load or vice versa, i would consider coupling lock/unlock phenomenon in my possibility list. if there is opportunity, i will inspect the gear teeth load profile
3) if the present TE is not placed at the coupling oil return line, you may want to study the present installation of the TE
4)infrared the coupling housing during both events. it may not help much in identifying th cause but it is wise to document this angle
5) other sensible suggestions from this forum
Things to ask yourself!
Are you using the correct viscosity oil for the application?
Is this a new problem to the machines?
What has changed?
Has the quantity of oil been checked?
How often do you need to run the compressor at the low speed v's high speed?
How long have these been in service?
When was the last oil changed?

We use a Caltex product in all our voith fluid couplings (torque fluid 32). Since we started using this we found we needed to adjust the oil levels slightly to get the correct soft starts that we required on our conveyors. This took some trial and error but has been worth it in the long run.

The Varnish that Paul talks about is an interesting concept but I'm not sure this to be the actual source of your problem. Is varnish a result of the oil degrading to a point? This would be considered as a secondary problem I think. As the varnish levels would not change weather it being at low speed or high speed of operation. I think the varnish would increase the temperature of the components but how does that change between low and high speed????

The amount of slippage between the coupling pieces is usually the place for generating heat within the couplings.
I would be looking for poor oil quality and worn coupling components after I answered the above questions.

Just some thoughts!


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