FOR MODELS: JGI, JGM, JGN, JGP AND JGQ SECTION 4 LUBRICATION
9/08 PAGE 4-3
or "degrade" to a lower viscosity, unless it is a multi-viscosity oil (such as SAE 10w40). In the
case of multi-viscosity oils, the viscosity improvers are breaking down, not the base oil itself.
Viscosity Index
A scale used to indicate the magnitude of viscosity changes with respect to temperature.
The higher the viscosity index, the less the viscosity decreases as the temperature
increases.
Pour Point
Pour point is the lowest temperature at which the oil will just barely flow. It becomes very
important in cold weather starting applications and in cylinder and packing lubrication with
very cold suction temperatures.
Flash Point
Flash point is the lowest temperature at which the oil will vaporize to create a combustible
mixture in air. If exposed to flame, the mixture will flash into flame and then extinguish itself.
This is important in high temperature applications when the oil may come in contact with air.
Lubricant Base Stock
Liquid lubricants commonly used in compressors include petroleum based oils and synthetic
fluids. All lubricant formulations start with base stock and lubricant additives are used to
improve specific properties such as:
• Increase the viscosity index
• Inhibit oxidation
• Depress the lubricant pour point
• Inhibit rust formation
• Improve detergency
• Provide anti-wear protection
• Provide extreme pressure protection
• Alter the friction characteristics
• Decrease the effects of gas dilution to resist "washing" of the lubricant due to water,
wet or saturated gas, or dilutent properties of the gas stream.
Petroleum-Based Lubricants (also referred to as mineral oils)
PARAFFINIC OILS
• Solvent refined or hydro-treated
• West Texas Intermediate or Arab Light
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