Figure 1. Sensor configuration of the
instrument air compressor. There are
also a number of imported process
parameters from this machine train
not shown here (these include suc-
tion and discharge pressure and
temperature, and motor current). The
bearing where high vibrations were
detected is shown in red.
02/08 ·
uptime
m
e
gazine
years since the upward trend first
started, the vibration level exceed-
ed the alert alarm limits once again.
It was decided to shut down the ma-
chine to investigate the problem.
After a quick investigation nothing
was found that required immediate
attention so the compressor was put
back into service. The vibration levels
remained above the alert alarm limits
so a series of tests were done by the
customer to try and identify the prob-
lem (e.g. changing the lubrication).
They were not able to reduce the vi-
bration levels, so Brüel & Kjær Vibro
was asked to look into it and evalu-
ate the problem. As the vibration lev-
els were increasing towards danger
alarm limits, the machine was shut
down .
t
Figure 2. The bandpass vibration lev-
el (black) from the inboard bearing
of the first stage impeller. The DC vi-
bration displacement (purple) shows
shaft position, (an offset change was
made at the end of 2006).