Compressor Synthetic lubricants
There has been much interest in recent years in the use of synthetic fire resistant lubricants based on phosphate ester, di-ester, glycol or silicone, which are used on their own or blended with mineral oils. They reduce the combustible mists and minimize carbonaceous residues on valves and piping; they are claimed to have a longer life and superior lubricating properties. One should be wary of changing to the use of such lubricants without reference to the compressor manufacturer, and certainly one should never attempt to mix them with each other or with conventional mineral oils, despite any claim that the two are compatible.
For high output reciprocating compressors, dibasic ester fluids are recommended; for refrigeration compressors, alkyl benzenes are used, and for rotary compressors polyalpha-olefines (PAO) are preferred.
Some of the problems that may arise are
• Incompatibility with metallic components.
• Incompatibility with the elastomers used in the diaphragms or seals.
• Plastics used in sight glasses or separator bowls may be affected.
• Paint used to coat the inside of pressure vessels or delivery passages may be softened and flake away, causing blockage of the filters.
• The cost will probably be higher (up to five times) than that of mineral oils.
• The lubrication properties may not be as good in the presence of water.
• The change periods may be shorter (although some suppliers claim an extended life).
• They tend to be more toxic, so precautions should be taken where the air is discharged into working areas.
However they appear to be a good answer to the problem of fire hazards, and should be considered where this is a problem.