070.250-IOM (APR 11)
Page 18
408 MM ROTARY SCREW COMPRESSOR
MAINTENANCE
MAINTENANCE
GENERAL INFORMATION
This section provides instructions for normal maintenance,
a recommended maintenance program, and troubleshooting
and correction guides.
WARNING
THIS SECTION MUST BE READ AND UNDERSTOOD BE-
FORE ATTEMPTING TO PERFORM ANY MAINTENANCE
OR SERVICE TO THE UNIT.
CAUTION
Cylinder assembly under high spring load. Consult
manual before disassembly. Improper disassembly may
cause injury due to spring tension release.
NORMAL MAINTENANCE OPERATIONS
When performing maintenance you must take several
precautions to ensure your safety:
1. IF UNIT IS RUNNING, PRESS [
STOP
] kEY.
2. STOP MOTOR AND LOCk OUT STARTER BEFORE PER-
FORMING ANY MAINTENANCE.
3. WEAR PROPER SAFETY EQUIPMENT WHEN COMPRES-
SOR UNIT IS OPENED TO ATMOSPHERE.
4. ENSURE ADEQUATE VENTILATION.
5. TAkE NECESSARY SAFETY PRECAUTIONS REQUIRED
FOR THE GAS BEING USED.
GENERAL MAINTENANCE
Proper maintenance is important in order to assure long and
trouble-free service from your screw compressor. Some areas
critical to good compressor operation are:
1. Keep oil clean and dry, avoid moisture contamination.
After servicing any portion of the refrigeration system,
evacuate to remove moisture before returning to service.
Water vapor condensing in the compressor while running
or more likely while shut down, can cause rusting of critical
components and reduce life.
2. Keep suction strainer clean.
Check periodically,
particularly on new systems where welding slag or pipe
scale could find its way to the compressor suction. Excessive
dirt in the suction strainer could cause it to collapse,
dumping particles into the compressor.
3. Keep oil filters clean.
If filters show increasing pressure
drop, indicating dirt or water, stop the compressor and
change filters. Running a compressor for long periods with
high filter pressure drop can starve the compressor of oil
and lead to premature bearing failure. Dual oil filters are
recommended so that the filters can be changed without
shutting down the package.
4. Avoid slugging the compressor with liquids (oil).
While
screw compressors are probably the most tolerant of any
compressor type available today about ingestion of some
liquid, they are not liquid pumps. Make certain a properly
sized suction accumulator is used to avoid dumping liquid
into compressor suction.
5. Protect the compressor during long periods of
shutdown.
If the compressor will be sitting for long periods
without running, it is advisable to evacuate to low pressure
and charge with dry nitrogen or oil. This is particularly true
on systems known to contain water vapor.
6. Preventive maintenance inspection
is recommended
any time a compressor exhibits a noticeable change in
vibration level, noise, or performance.
CHANGING OIL
WARNING
DO NOT MIX OILS of different brands, manufacturers,
or types. Mixing of oils may cause excessive oil foam-
ing, nuisance oil level cutouts, oil pressure loss, gas or
oil leakage and catastrophic compressor failure.
Shut down the unit when changing oil. At the same time all
oil filter cartridges must be changed and all oil strainer ele-
ments removed and cleaned. The procedure is as follows:
1. Stop the compressor unit.
2. Lock out the motor starter.
3. Close the suction and discharge service valves
4. Using appropriate equipment, lower the compressor
pressure to 0 psig.
5. Open the drain valve(s) and drain oil into a suitable con-
tainer.
6. Drain the oil filter(s) and the oil coolers.
7. Remove the old filter cartridges, and install new ones.
8. Remove, clean, and reinstall elements in the strainers.
9. Evacuate the unit.
10. Open the suction service valve and pressurize the unit
to system suction pressure. Close the suction valve and
leak test.
11. Add oil.
12. Open the suction and discharge service valves
13. Remove the lockout from the motor starter.
14. Start the unit
RECOMMENDED MAINTENANCE PROGRAM
In order to obtain maximum compressor performance and
ensure reliable operation, a regular maintenance program
should be followed. The compressor unit should be checked
regularly for leaks, abnormal vibration, noise, and proper
operation. A log should also be maintained. Oil analysis
should be performed on a regular basis. It is a valuable tool
that can identify the presence of moisture, acid, metallics
and other contaminants that will shorten compressor life if
not corrected. In addition, an analysis of the compressor
vibration should be made periodically.
VIBRATION ANALYSIS
Periodic vibration analysis can be useful in detecting bearing
wear and other mechanical failures. If vibration analysis is
used as a part of your preventive maintenance program,
take the following guidelines into consideration.
1. Always take vibration readings from exactly the same
places and at exactly the same percentage of load.
