Just when you think you have seen it all....

Customer calls to complain about high axial vibration on a center hung fan that has just been rebuilt with new shaft, bearings, sheaves and belts.

Axial velocity levels are in excess of .98 IPS at 1X.

Bearings look good, alignment is checked and good. Everything is tight....I exhaust all standard analysis checks. I continue to ask questions of personnel and anyone who has worked on this fan.

Finally find out that that upon startup the fan kept tripping out....hummmmm OK...anything else?

Well, the contractor says he put the fan back together the way they found it. That may be a problem. People working on fans that don't know anything about fans. Finally I strobe the rotor and stop it for inspection while running (can't shut down due to production) I see that the rotor is a backward incline design and has been installed backwards.

Contractor says the shaft was keyed a certain way and that was the only way it would install....sooooo they just put it in like that.

Thinking the problem is solved....I get a call back stating that the vibration is still high. Once again I do a visual inspection and find that the fan rotor is still installed backward but the contractor reversed the motor rotation thinking that would help!!!!! ARGGGGGHHHH

Can you believe that there are contractors working in major US steel mills that do that kind of work....

I had to go have several cold beers after that one! Anyone else see that kind of nonsense???

Also in a steelmill, 2 fans medium size was found to be run backwards and had been like that for 10+ years, so they still are, nobody dared to change it as it had been working. Vibration was not that bad anyway.... Olov

I was workingon a sander dust fired boiler where i used to work. THey caled and said boiler wouldn't hold pressure. I scratched my head and anything else i thought would help.When we switched back to gas i saw the blower that feeds the dust to the boiler coast down and it was running backwards. Who knows how long it had been that way. I just reversed and everything worked fine. I guess we had enough forced draft it was just sucking the dust out of the silo intothe boiler.

WHo would thunk it

In the time it took to move from the end of the paragraph where you said the fan was installed backwards to the beginning of the next paragraph, I had the idea to reverse the direction of rotation and the realization that it wouldn't work. That really wasn't a very long time. It seems like in the time it took to rewire the motor leads, someone would have come to the same realization.

Have one of those cold ones for me too.

At first glance, I'd have thunk that would work (good thing I'm not a contractor). But of course (for those that are slow like me), they also would have needed to reverse the stationary fan components (casing) in order for everything to work correctly as a mirror image of original configuration. Otherwise you end up with something like a fan rotating CW with the discharge scoop set up for air exiting in the CCW direction.

Still a funny story.

Too bad the rotor didn't have radial blades, then the contractor whould have got it correct! Perhaps the contractor was using a mirror during rotor assembly while combing his hair!

Walt

So much work. Why didn't they just turn that little direction arrow on the fan housing so it pointed the other way. :P

For probably 20 years, two of our hydraulic power units ran hot. The solution was to install hoses to spray water on them in the summertime. When I arrived to see that, I used my non-contact thermometer to trace the heat pattern. The heat pattern was exactly reverse of what you would expect.
The heat exchangers had gear pumps to move oil through them. The pumps were running backwards, sucking air from the top of the tank, instead of oil from the bottom! We reversed the pump motors--no more overheating!

quote:

Originally posted by Ron Stiemsma:
So much work. Why didn't they just turn that little direction arrow on the fan housing so it pointed the other way. :P

That one gave me a good chuckle....The customer actually asked me what I thought about moving the motor and sheave assembly to the other side of the fan housing....

I don't think he was thinkin either...

These people spend hours trying to think up different ways to fix the problem and non of them come close to the correct fix....

I got a real good idea...How about we pull the inlet, yank the shaft and rotor and put it back together the RIGHT way....Oh, and call the electrician too.

The same contractor that installed the fan Wrong was just in this past week and welded about 200 lbs. of steel bracing on the fan h ousings to STOP the excessive axial vibration....that lasted 2 days....Friday I hear that they broke the bearing plate and wiped out the new bearings.

I thought we were trying this new thing called RCM...these people keep shooting them selves in the foot.

Great call Webcruiser. Did you learn that from me?

Ha, Vibeguy2004, did I learn ANYTHING from you?! Just kidding! I would love to get some more tutoring if we can swing it from this end.

Hey, you are so right about these forums. Thank God (Allah, whoever) for them.

Mr. Reliability,

Some questions:

1. Are you linking backward rotor installation with excessive 1x axial vibration as cause-and-effect? If so, why ?

2. Had they ever corrected the installation and did axial vibration drop down afterwards?

3. Weren't there in the vibration data other symptoms of backwards installation, such as unusual Vane Pass or low head pressure?

David

This message has been edited. Last edited by: David_G,

Instead of reply- One question- Can the change of coupling from pin and bush type to tyre coupling reduce axial vibration in overhung fan rotors? Or, loose bushes in pin and bush type couplings have anything to do with high axial vibration in such case?
Regards
Irshad Akhtar

I assume you have checked that the blades are backwards leaning by design and not forward leaning by design?

Was called to check the alignment of newly rebuilt pump/motor set because it was drawing high amps and tripping the motor. Misalignment won't cause that I said. "Oh yes it will...we read that in a magazine." Did the alignment (it wasn't out much) and of course it still drew high current. I had them start closing the discharge valve and the amps didn't change (reduced flow = reduced amps on a centrifugal pump). Strobed it and it was running backwards. "Not possible" the mechanic said, "it's running the same direction as the other pump right next to it." Of course the motors were mounted tail-to-tail.

Was called to "balance" a fan because it wasn't moving enough air. Imbalance won't cause that says I. "Well, we want you to balance it anyway." When I started to attach the trial weight I realized the new, backward curved centrifugal wheel was mounted backwards. I also noticed there was no "inlet cone" and there was a 6" gap between the duct inlet and the fan wheel. "What did y'all do with the inlet cone?" "There wasn't any inlet cone." Turns out they'd replaced a paddle wheel fan with a centrifugal. But hey, a fan moves air right? That's all you need to know apparently.