Page 126 - Reciprocating Compressors Operation Maintenance

Operation and Maintenance of Reciprocating Compressors 113

inhibitors and should display good anti-foaming qualities. The anti-foam-
ing properties are particularly important in compressors using splash or
flood systems.
At normal ambient temperatures, the oil should have a minimum vis-
cosity of 200 Saybolt seconds at 130°F. This is equivalent to a SAE 30,
or ISO 100 grade lubricant.
It is not desirable to use a detergent-type oil, and, if for any reason a
change is made to an oil with detergent characteristics, the entire oil system
must be thoroughly cleaned soon after start up. Dirt and deposits, which
will be loosened by the detergent oil, must be flushed from the system.
Experience has shown that it is false economy to use an inferior, low
first cost, and poor quality oil.

Frequency of Oil Changes

It is not practical to pre-define how often an oil should be changed,
The oil will become contaminated with foreign material being held in
suspension as well as moisture due to condensation; therefore, the time
interval for oil changes is governed by the operating and local ambient
conditions.
It must be remembered that the oil charge will not last indefinitely, and
certainly if the compressor is shut down for an overhaul, it is poor prac-
tice not to completely clean the crankcase, change filters, and install new
oil at this time. Periodic oil analyses are strongly recommended in an
effort to determine optimum change frequencies. In addition to moisture
content and viscosity stability, total acid number (TAN) and flash point
may be worth tracking and trending. Lubricating oil analysis for compo-
nent wear is an excellent maintenance technique.

CYLINDER AND PACKING LUBRICATION

In contrast to the lubrication of crankcase and bearings, the lubrication
system for compressor cylinders and packing must be able to reliably
deliver relatively small amounts of oil at higher pressures in order to
lubricate the wearing surfaces of cylinders and piston rods.
Cylinder and packing lube systems are terminating or "once-through,"
systems. The volume of oil delivered at each point needs to be just
enough for proper lubrication. Therefore, the rate of lubrication at each
point is critical, and over lubrication must be avoided.