Hydrocarbons are the least expensive lubricants on a “cost per gallon” basis, but the most expensive on a “cost per year” basis. Because they are inexpensive, they are useful for very contaminated chemical environments where contamination means that frequent changes will be required.
Hydrocarbons are subject to varnish formation if run beyond the recommended life, which is typically about 1000 hours. Both flash point and carry over are linked to volatility. The higher volatility of hydrocarbon oils also results in higher carry over. Typical examples of this type of fluid include ATF(Dexron), motor oil, turbine oils, R & O oils.
► Inexpensive (per gallon, not per year).
► Good for very contaminated environments.
► Varnish Formation
► Very Limited Life
► Lower Flashpoint
► Higher Carry Over into the Air System
PAO / Synthetic Hydrocarbons
PAO’s are also known as Synthetic Hydrocarbons. They are also a significant improvement over standard petroleum oils boasting a longer life and has good compatibility with petroleum oils.
PAO’s are subject to varnish when the antioxidant in them is depleted. Compressor service technicians have reported that the varnish left by PAO’s is sometimes even more difficult to remove from a compressor than that left by petroleum oils.
Synthetic Hydrocarbons are the only fluids which are eligible for the USDA H-1 rating for incidental food contact. The H-1 rated PAO’s typically have a life span in the range of 2000
Other PAO’s are rated from 4000- 8000 hours.
Nearly all of the automotive synthetics on the market are PAO fluids. They are regarded highly for this application.
► Longer life than petroleum hydrocarbons
► Also used in contaminated environments
► Good compatibility with elastomers.
► Best Food Grade option (H-1)
► Varnish Formation is not very predictable
► Moderate Carryover
Diesters were one of the earlier types of synthetics used in compressor, automotive, and other applications. They are still used extensively in reciprocating compressors today.
Diesters are the most aggressive to some of the common types of rubber and elastomers found in compressors and compressed air systems. In addition, diesters in the presence of water hydrolyze causing sludge formations.
Diesters have been around for a long time, but other types of synthetic fluids are gaining much more popularity in rotary compressors.
► Used as reciprocating compressor fluid
► Deposit formation
► Attacks many solenoids, seals, hoses, and plastics.
► Moderate carry over.
► Some implicated as endocrine disruptors
Polyglycol/POE lubricant fits the needs of rotary compressors very well. In rotary compressors, the lubricant cools, lubricates, seals rotors and protects against corrosion.