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Figure 6 . Burnt oil on the
third stage impeller bearing
Figure 5. Scratch on the second
stage impeller bearing
After Repair
The manufacturer replaced all the
bearings and the intercooler drain
lines were checked for proper drain-
ing of water to avoid carry-over. The
inlet air filter was also thoroughly in-
spected for damage and openings.
Fig. 7 shows a spectrum plot (con-
stant percentage bandwidth meas-
urement of 6% centre frequency)
where the third order harmonic for
the most part disappears.
Figure 7. The 3rd order harmon-
ic disappears from the spectrum
(cpb6%) after the bearings are re-
placed
Conclusion
Brüel & Kjær Vibro's COMPASS sys-
tem successfully detected a fault at
an early stage of development while
the compressor was still under war-
ranty. The monitoring system played
a vital role here since four harmonics
are individually monitored. The vibra-
tion response of different machine
faults manifests itself with different
harmonics, and in this case it was
the third harmonic that gave the ear-
liest indication of a bearing fault. The
fault was slow to develop, so long
term trend capability was necessary
to follow its progression.
Diagnostic assistance provided by
Brüel & Kjær Vibro was able to deter-
mine that it was a bearing fault. The
compressor manufacturer was con-
tacted, and by looking at the vibration
data during their root cause analy-
sis, they were able to determine that
one bearing was failing prematurely
due to a manufacturing fault. There-
fore all bearings were replaced while
the compressor was still under war-
ranty.
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