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Walt Strong

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Reply with quote  #16 
"then want me to fix it by making it not shake at .3 ips." What is shaking; fan, ducts or something else?

Damper pressure loss is only one factor can affect baghouse performance. A system diagram and other data would be needed to evaluate the problem; note that problem is poorly defined! If fan is shaking at 0.3 ips, then it may be operating away from the best efficiency point (BEP). If airflow is low, then fan(s) may be operating "back on the curve" that can cause high blade-rate pulsation, low frequency turbulence and/or surge/stall under severe conditions. 

Walt
Danny Harvey

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Reply with quote  #17 
.3 ips peak horizontal on the fan. A beat frequency between 3 and 4 (closely spaced speeds) and the Scalper makes it go to about .5 or so up at whatever beat those speeds, orientations, stiffnesses, masses, etc add up to. 

The point is that vibration is not the problem. Air flow is. Fix that first and you might not have a vibration problem. Making those fans spin smoother is not going to help with that. And this is not something that you can fix by watching a youtube video.
Walt Strong

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Reply with quote  #18 
I have worked on several power plant fans with a high noise or vibration problem, and they were resolved by addressing fan and system performance. Rotor unbalance or shaft misalignment (1xSS) were not the source of the problem. What is the dominant frequency of your fan vibrations? Did the flow expert do a performance test for each fan? I have not made any U-tube videos on this subject! 

Walt
Danny Harvey

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Reply with quote  #19 
Not only is 1 x shaft speed not the cause of their problem, it's likely going to change when they fix the real problem.

I never really checked youtube but it wouldn't surprise me to find a video on the subject there.  

I think that I have convinced them of the difference between the types of balancing and that they aren't going to get more air from a better spin. Last I heard, Maintenance was going to toss it back to Engineering and tell them to fix it.

The discussion might have identified part of their problem which is the question of damper position.

Thanks to all.
electricpete

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Reply with quote  #20 

The idea that balancing a fan (in the rotating equipment sense) is going to increase flow is funny.  Some people would just take their money and let them figure out their mistake later (after all it was running a little rough anyway, so the balance effort was not wasted!). But I know you're not the kind of guy that would let them go down the wrong path without explaining that. 

I still say you can give them helpful data with a trend of slip over time on that motor or with slip compared to nameplate slip if you have either of those.  Slip is more linear with motor output than current is (current can be 25% or more at no load).  Both slip and current share the same vulnerability to voltage variations.  And if they don’t have any historical record of current at all, the historical slip information would be all the more valuable to figuring out what has changed. 

 

Danny Harvey

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Reply with quote  #21 
Pete,

I have to admit, my reasons for not wanting to do this are not entirely altruistic.

It would have to take place on a Saturday during a 12 hour outage and if we hope to accomplish anything, all three fans are going to have to be balanced and trimmed, then trimmed again and maybe again so that when the two big ones come into phase and the match the little one, our resulting force is low enough to keep from deflecting the beams that they are mounted to. Then, there would be the moment where it doesn't shake too much but still doesn't work right and the "What are you going to do now?" question. My answer would be the same as it is now but my bill would be outrageous and my reputation would suffer. So I would be wrecked with this client and they would be no better off. That's why I told them that I would not do it.

I'm trying to tell them that those 12 hours would be much better spent with a real live dust collector fan system expert doing whatever it takes to return this system to it's original function.

In this case, I don't do the regular program and don't have access to the data. I help their guy when he is in over his head.

I told him to review his data wherever he gets the best resolution on the fan and motor speed which is the 12,000 cpm/1600 lor that I had him add to every motor he covers.  I had him add one to this fan, too.

I like to keep clients happy, but sometimes they need to be protected from their desires for simple answers to complex questions.
dnk

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Posts: 63
Reply with quote  #22 
What is the baghouse collecting? If it is collecting solids it is possible to have buildup in duct which will have effect on pressures and volume of air moving through duct. This can also have effect on fan vibration. I have seen vibration reduction just from cleaning ductwork. 
also when collecting data make sure you are 4 to 5 diameters away from any elbow(not positive on # of diameters).
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