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Noknroll

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Got this plane bearing motor 4pole 50Hz Driving a step up voith variable speed fluid coupling gearbox to boiler feed pump.
This odd frequency, 8.125 Hz/ 0.327 orders has just appeared at the motor NDE bearing nothing else in the drive train runs at this frequency. Only thing that crossed my mind was oil whirl/whip but I believe this is closer to 1/2 x 
Any ideas?
John from PA

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I agree that this seems low. I generally see in the literature something like 40% as the low end, but I have personally been involved with a gearbox that exhibited about 38%. It was however a bearing that had been installed incorrectly causing excessive clearance.

In my experience another characteristic of whirl is high amplitude. Levels are commonly 50% of bearing clearance or more. Is that happening in your case?
Noknroll

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John, this is only casing measurement, clearance unknown, amplitude 0.75mm/sec, while 1 X peak is only 0.1mm/sec
Walt Strong

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Not Oil Whirl/Whip, but could be nonlinear rub at 1/3 xSS.

Walt
Noknroll

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Thanks Walt,
just progressing through the machine with my analysis and found that the booster pump, also plain bearing has had a similar mystery low frequency vibration appear at the 1840 rpm booster pump at  7.26 Hz/0.23 order. Lube system is the only common link I can see.for those not familiar with this equipment attached is a rough sketch. EFP vibration.JPG

Curran919

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Did you have the 8.125 Hz and 7.26 Hz vibe at the same time (at their respective locations)?
Walt Strong

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I am currently working on a similar but different boiler feed pump train consisting of (in order) booster pump, motor (14,000 hp at 1800 RPM nominal), Voith speed increase gearbox, and main BFP (variable speed). All components have journal bearings with the exception of the booster pump that has ball bearings. I am focusing on booster pump vibrations that includes an issue with pump seal (plan-23) cooling water pipe failures. The two frequencies you mentioned above are in the same range as natural frequencies of the cooling water pipe pipes. I could say a lot more, but you might want to investigate for natural frequencies of the cooling plan water pipes or the main suction and discharge pipes. Either of these pipes are good candidates to produce low frequencies that are bothering you. Happy hunting!

Walt
Noknroll

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Reply with quote  #8 
Curran, the readings were in the same survey, but probably 5 mins apart by the time i got from one end to the other.

Walt come to think of it i did make a mental note at the time that mech seal water pipes on booster pump had a bit of a shake on. Forgot where i filed it till you mentioned it :-)

Back on site next monday, ill do some more hunting
marksl

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Quote:
Originally Posted by Noknroll
Curran, the readings were in the same survey, but probably 5 mins apart by the time i got from one end to the other. Walt come to think of it i did make a mental note at the time that mech seal water pipes on booster pump had a bit of a shake on. Forgot where i filed it till you mentioned it :-) Back on site next monday, ill do some more hunting


Did you find the source of the 0.327 orders
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