FOR MODELS: JGW, JGR AND JGJ SECTION 4 - LUBRICATION AND VENTING
PAGE 4 - 2 1/01
Cold Starting
If a compressor is exposed to cold ambient temperatures, the oil system must be designed
so the unit may be safely started with adequate oil flow to the main bearings. Temperature
controlled cooler by-pass valves, oil heaters, cooler louvers and even buildings may be
needed to ensure successful operation. Cold weather installations may use multi-viscosity
oils in the compressor frame if the oil supplier can certify that the oil is shear stable.
The vis-
cosity of shear stable oil does not degrade through use. Multi-viscosity oils are subject to a
shorter oil life than single grade oils by 30% to 50%.
Compressor Prelube Pump
All electric motor driven compressors and all unattended start compressors with any type of
driver must have an electric or pneumatic driven prelube pump to ensure oil flow prior to
start-up. Motor driven prelube pumps should be sized at 30 psig (2.0 bar
g
) and a flow rate
equal to half the flow rate of the compressor frame lube oil pump (see Table 1-1 on page 1-
2 and Table 1-2 on page 1-3). A start permissive should disable the start-up sequence if oil
pressure is below 15 psig (1.0 bar
g
). A compressor prelube cycle is strongly recommended
for all compressors to extend bearing life.
Liquid lubricants commonly used in compressors include petroleum based oils and synthetic
fluids. Lubricant additives are used to improve the viscosity index, inhibit oxidation, depress
the lubricant pour point, inhibit rust formation, improve detergency, provide anti-wear protec-
tion, provide extreme pressure protection, improve “lubricity”, decrease effects of gas dilu-
tion, increase “wetability”, and resist “washing” of the lubricant due to water, wet or saturated
gas, or diluent properties of the gas stream.
• Viscosity index is a measure of the ability of an oil to resist the thinning effect caused
by increasing the oil temperature.
• Lubricity is the “slipperiness” or ability of a lubricant to decrease friction.
• Wetability is a measure of the ability of the lubricant to adhere to metal surfaces. An
increase in wetability increases the lubricants’ resistance to “washing” effects.
Petroleum Based Oils - also referred to as mineral oils:
Paraffinic - higher wax content, better resistance to thinning at higher operating tempera-
tures than napthenic.
Napthenic - (as compared to paraffinic) lower wax content, better flowability at low tempera-
tures for cold start-ups, lower resistance to thinning at higher operating temperatures, better
solvency, lower life/oxidation stability. Napthenic oils leave softer carbon deposits/residues
on discharge valves, etc.
Compounded Cylinder Oil Additives
Cylinder oils are specially compounded lubricants designed for use in steam cylinders and/
or compressor cylinders. Compounded lubricants can be petroleum or synthetic base. Addi-
tives can be animal, vegetable, or synthetic base. These lubricants are formulated to
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