Identifying the source of vibration by following the amplitude: the case of a company that thought the problem was a pump impeller, but, in fact, the problem was over 15-ft away and not a pump at all.
Many times we will bury ourselves in a problem looking at endless spectrums, waveforms, and machinery information in search of the source of a vibration problem, while forgetting the very basics of vibration.
Consider the following example at a large brewery. They had an unusual layout of three variable-speed pumps drawing water from a manifold system fed by two input pipes. When the production demand for water exceeded the capabilities of one pump, the second pump would be automatically started by a programmable logic control (PLC) system.
Accordingly, the two pumps would slow a bit until water demand again had both pumps running at near maximum capacity, when the third pump would kick in. Again, all three pumps would slow down to match demand. A major problem appeared when the second pump kicked in and the speed slowed. As the two pumps sped up, the vibration seemed to disappear. When the third pump kicked in and all three pumps again slowed down, the vibration was approaching 0.6-in/sec RMS.
