Page 130 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 117

RATE OF OIL FEED

The amount of oil fed to the compressor cylinders should be sufficient
enough to provide lubrication and effectively seal the piston against leak-
age. Oil feeds above this amount are wasteful, cause oxidation, and tend
to increase oil carryover to distribution lines.

Excessive Oil Feed

All oil fed to the cylinders is subjected to oxidizing conditions. Under
prolonged heating, even the best quality compressor oils will oxidize to
some extent. Therefore, feeding more oil than is actually needed results
in increasing the amount of oxidation products formed.
Because the highest temperatures are encountered on discharge valves
and in discharge passages, and most of the oil fed to the cylinders even-
tually leaves through the discharge valves, it is here that deposits tend to
accumulate. To prevent or minimize trouble from deposits, an oil espe-
cially suitable for compressor service that permits using very low rates of
oil feed should be used.
Feed rates for compressor cylinder lubrication are typically shown in
drops per minute; however, the principal difficulty with the pumping
elements of box type lubricators is that the measurement of drops is not
reliable.
Consumption per 24 hours, not the number of drops, is the proper way
to determine feed rates because drops vary in size and there also is a vari-
ance between the specific gravities of the sight glass liquid and that of
the lubricating oil. Use the number of drops merely as an estimate and as
a way to obtain a balance between cylinder feeds.
The quantity of oil required to provide ample lubrication for any com-
pressor cylinder is obtained by the formula:

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Gallons/24 hours = diameter (in.) x stroke (in.) x RPM

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Drops/minute = diameter (in.) x stroke (in.) x RPM