viscosity increase of refrigeration oil

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A screw compressor (CM802 FES132E ) uses VG46 refrigeration oil (mineral), refrigerant: ammonia. The oil viscosity increased up to 70-90 cSt after using 1-2 months. If drain and stay for several weeks, the viscoisty decreased to 50 cSt. Anyone had such expriences and tell me why and your solutions? Thanks.

6/28/069:22 PM

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Original Post

refrigguyMember

It is not uncommon to see viscosity increases with ammonia and mineral oils. The increase is usually one VG grade over a period of several months, then it stops increasing and becomes stable for an extended time period.

Some blame the viscosity increase on evaporation of the light components of the oil from the compressor oil. If you are seeing the oil level drop in the compressor, then the volatility may be the cause of the viscosity increase. The light compnents of the oil may be accumulating in the evaporator and will likely need to be drained out and returned to the compressor.

Another possible explanation is the chemical reaction of unsaturated hydrocarbon components and / or sulfur based compounds in the oil catalyzed by ammonia to form higher molecular weight compounds. This may result in insoluble sludges if it continues.

7/6/067:14 AM

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