Page 140 - Reciprocating Compressors Operation Maintenance

126 Reciprocating Compressors: Operation and Maintenance

ing temperature) increases with pressure, and in the case of certain gases,
condensing temperatures that are above cylinder wall temperatures are
reached as compression proceeds.
Under such conditions, part of the gas in contact with the cylinder wall
is cooled to the condensing temperature and liquefies. The condensate
formed will do the following:

* Tend to wash the lubricant film from the cylinder walls
• Dissolve in the lubricating oil, reducing its viscosity.

Viscosity reduction in service due to these effects should be compen-
sated for by the use of a heavier-bodied oil than would be otherwise
selected.
In addition, higher than normal jacket water temperatures are advisable
to prevent or minimize condensation, which requires heavier-bodied oil.

CHEMICALLY ACTIVE GASES

Obviously, compressor parts must be made of metals that will resist
corrosion by whatever gas is handled. It is the effect of an active gas on
the lubricant that is of interest.
With some gases, such as oxygen, petroleum products must not be
used. Chlorine reacts with oil to form gummy sludges and deposits.
Methyl chloride or ethyl chloride and sulfur dioxide also may form
sludges in the presence of oil, moisture, and selective additives.

SYNTHETIC COMPRESSOR LUBRICANTS

Synthetic oils have become more widely used and accepted as com-
pressor lubricants because of their higher "auto-ignition" characteristics
and ability to prevent carbon buildup on valves and piston rings.
The use of synthetic oils may allow the reduction of feed rates to the
cylinder by approximately one third. This reduction in feed rates will
result in less oil in the downstream piping system. Reduced oil accumu-
lation and the "fire resistant" characteristics help to prevent fires in the
discharge lines. However, no oil is fireproof or explosion proof.