Howdy,
Has anyone out there ever had vibration problems with a Gyrol fluid drive. I believe the one we're having problems with is a Class 4. We've had it sent off to the OEM twice, and all mechanical specs are good. Alignment and balance is good, minimal noise in pump and motor. All noise is in the fluid coupling, radial (horizontal) dominant peaks at output shaft frequency. The noise is cyclical. Output 1x increases from .5 mils to 5 mils for about 5 seconds then drops back down to .5 mils for about 20 seconds, then repeats. We think it's a resonance of some kind but we don't know where to look. We checked the natural frequencies of the rotating assembly and they're way above the input and output speeds (3600 and 2700-3200 respectively.)
Any idea's out there?
Thanks,
Gary

Could be a beat. Not real familiar with fluid couplings. But the one time I did monitor some fluid couplings the motors were running one speed and the input of the gearbox was running another. There was only about 10 CMP difference between the two and the waveform looked like a beat. Don't know if this is typical or not. Hopefully I will learn something from your post.

Gary,
It sounds like you might be getting a beat from another machine.

This fluid coupling is driving a large Boiler Feed pump. It is near two other boiler feed pumps, but only 2 run at any given time. The other operating unit (no matter which other one is in operation) doesn't show this noise. They are all mounted on concrete bases, approx. 15 feet away from each other, on the bottom floor of a power plant. They are not near any other significant equipment.

Just for those who don't know what this fluid coupling is: This fluid coupling is basically a big box with two shafts that meet in the middle. One shaft is driven by a motor, and the other shaft drives the pump. Each shaft has two sleeve bearings and a thrust bearing. Each has an impeller where they meet, oil is forced into the impeller, and the movement of the oil by the drive side impeller causes the output side impeller to turn.
The positioning of the scoop tube that removes the oil from the impeller is what sets the output speed. Our input speed is constant at 3470 rpm, the output varies from 0 to about 3300 rpm, normal operating speed is around 3200 rpm, and the noise shows up between 2700 rpm and 3200 rpm. The two shafts are not physically connected to each other.

Hope the additional information helps.

Will the time interval of the maximum vibration vary from running 2700 RPM to 3300 RPM?
If it is, it would indicate beating btw. incoming and outgoing speeds but it would be a pretty quick variation so it´s not likely, more to be able to set one idea aside. Olov

OLI, as a matter of fact, the time between the increases does change. As the speed increases from 2700 to 3200, the time between beats increases as well. It starts out about 18 - 23 sec between pulses at 2700, by the time your at 3200, the time between pulses is approx. 35 sec. The beat itself lasts about 5 seconds and does not change with speed changes.

I'm not really familiar with fluid couplings, but from your description could it possibly be that the gap between the driver and driven is varying slightly creating a recirc condition in your oil. Just thinking out loud

Gary,
I have worked on a Voith fluid drive with KSB boiler feed pump rated 2000 hp with motor speed of 3775 rpm. I dealt with shaft alignment, balancing, and resonant coupling issues on this project. Anyway, regarding your symptoms, I would measure 1xSS amplitide and phase of output shaft. If this vector is changing in a circle or spiral pattern on a polar plot, you may have a rub (oil seal, scoop tube, or bowl).

Mr. Vibeman--

I have several "Gyrols" on-site, mostly used for back-up (on for turbine driven boiler feedwater pumps) except for one that's run continuously for almost a year now (problems w/turbine keeping up). There is a definite beat and it would be expected that as output speed increases (and approaches input speed) that the beat "frequency" (time between beats decreases).

In non-engineering language (that's all I know), the reason for the latter is that--as the two speeds approach each other, they spend more/longer time in phase w/each other--and also out of phase w/each other. Mathematically, I think we're talking about the inverse of the difference between the two speeds being the "period" of the beat.

I've not known much about the inner workings of these little jewels, but have trusted/hoped that trending (relative to output speed) would show any problems or "wear" developing inside.

Walts suggestion re: phase sounds very helpful too.

Tony

Thanks for the ideas guys, at least we've got some direction now.
Gary