Every once in a while when observing spectrums I come across non-synchronous peaks and harmonics that do not match up with the bearing defect frequencies that are setup for the particular machine.
The actual bearings in the machine have been verified, but on occasion I still read spectrums with these seemingly unrelated peaks and harmonics which I cannot explain.
These are horizontal centrifugal pumps with brass oil rings(slingers).
Is it possible these rotating oil rings could somehow be creating these frequencies?
Thanks in advance,
Robbie

Doc1.doc (46 Kb, 60 downloads)

I would have a hard time believing that the oil rings can create periodic impacting at 5.6 times running speed. Oil rings rotate slower than the shaft. But you never know.

My best guess would still be bearing fault frequency, especially if the accleration time waveform looks like impacting. Sometimes there are changes in bearing manufacture which can affect the fault frequencies even within the same manufacturer/part number.

I agree with Pete. It still sounds like bearing harmonics. Which software package are you using? I'm currently using Entek Odyssey which allows me to select a manufacturer and bearing Nº and will then only display one set of frequencies for that bearing. Previously I used CSi RBMware, which would display every variation of the same bearing by a manufacturer. You may find out that for a given bearing there are a number of different modifications, some of which include an extra roller, which will alter the defect frequencies considerably.

I seem to remember a while back that someone started a thread on this forum about possible sources of non-synchronous peaks. It may be worth a search for it.

Sometimes a nearby machine may be the source of non-synchronous peaks.

I use SKF Machine Analyst Software.The specific bearing defects are loaded for each machine depending on the actual bearing that is in the machine at the time.
During repairs the mechanics save the old bearings and the new bearing boxes so that there is no question as to what particular bearings are actually in the machine.From this I examine the old bearings and document the exact bearing that is going into the machine which is then inputted into the software for defect frequencies.
In this case the bearings are SKF 7313BECBY (THRUST) and SKF 6214 (RADIAL).I could not find any defect matches from either of these bearings.
I do realize that the spectrum does not show a big problem at this time, but this issue has come up in the past on other equipment where the defect freqs. do not match up which are much more serious.
I also take a demodulation reading (enveloped acceleration) which usually matches the defects shown in the velocity spectrum.
I included the env. acc. spectrum to compare.
Thanks

Doc2.doc (44 Kb, 38 downloads) env. acc. spectrum

I agree with others, smells like a bearing fault, although may not be severe. One explanation of not matching the fault frequencies in part may be derived from an inaccurate measure of the RPM. Second - from using slightly different bearing stored for this machine in the Dbase. For example,
SKF 6214 : BPFI=6.44x, 11 balls
SKF 6214E: BPFI=5.97x, 10 balls

I agree, looks like a bearing defect. Did you collect a plain g's spectrum, looking up to at least 120k. Look for the same frequencies there and that should help you determine the severity.