Mine are Amarillo Mounted Tuflite-II fans 28ft dia. It was reported that one cell has high noise in comparison with others. Its all parameters were all within recommended limts, I mean track, end clearance etc. but still the noise is more. Any idea as to what could be the cause?

What kind of noise, the kind which does not show up in vibration data?

iS this noise due to air movement or do you think it is related to gearbox noise?

John from PA

Are there any restrictions in airflow? Is the speed (RPM) the same?

Yahoo,

You haven't been very specific, but here are a few things to check for high/unusual sound:

Fan Noise/Vibrations
Excessive/unequal blade pitch
Uneven/tight blade tip to fan stack clearance
Damaged or loose fan blade
** Loose or missing fasteners on fan stack

Gearbox Noise/Vibrations
Gear lube poor condition or incorrect quanitity
** Worn gears or bearings
Loose base bolts or structural supports
Drive shaft unbalance, misalignment or worn couplings

Motor Noise/Vibrations
Loose base bolts
Loose fan shroud bolts
** Poor bearing lube or worn bearings
Rotor/stator electrical fault

Let us know what you find out.

Walt
w_f_strong [at] msn [dot] com

Check the end of the blade tips - there should be a "weep" hole that goes through to the inside of the blade for condensate removal. I found one a few years back that had an additional hole drilled off to the one side of the weep hole that did not go all the way through. This turned into a very high pitched whistle at 1x rpm. It did not show up in the vibration spectra but showed up very nicely when noise meter was attached to the analyzer. Anyway, the quick fix was a piece of duct tape to prove the point. The guys went back later and filled the hole with epoxy - which solved their problem permanently.
Hope this helps,
Pat

You can have a perfect set of blades, perfectly positioned in the hub, perfectly balanced, and still have high noise levels. It's very difficult to make a perfect shroud however. I expect there is a location (or several) where the tip clearance at the shroud varies.

Thanks for your attention guys.

quote:

iS this noise due to air movement or do you think it is related to gearbox noise?

The noise feels like air from fan blades. May be due to uneven gaps, I mean tip clearance.
But when checked following were the observations:

Tip clearance : 12mm (Max. Allowed:3/4")
Track: 22mm (Max. Allowed:3/4"-1")
All fan blades within +-0.2deg of 16 degrees.

No cooling holes (total 02 ) plugged.


"Loose or missing fasteners on fan stack" is a condition that exists but then it is so on all other cells why this one ?

Regards

Also, check the blade pitch, if it is adjustable. You can do this with an inclinometer, or even a good bevel gauge.

Yahoo,
How many cells are connected or how are they arranged? If there are say 3, is this the center cell? Location of the cell can determine the audibility of the cell. If there are fewer exit paths for the sound waves or more hard surfaces around the cell to reflect the sound waves, it can make this cell seem louder then sister cells.
I am assuming that this must be a new installation. Any extra info would help to assess your issue.

yahoo, are you saying that you checked the tip clearance around the full 360 degrees of the shroud? What I'm suggesting is the fan is not centered in the shroud, or there are locations where the clearance varies due to variations in the shroud geometry.

To me this is analogous with a package boiler where the burner is not centered in the air inlet cone... they will make a lot of noise, sometimes can be heard from a half mile away.

Yahoo,

I suggest that you measure sound pressure level and spectrum at several locations including on fan deck, above fan stack, near drive motor, and on ground or near fan inlet. You can't always trust your hearing to diagnose an actual or apparent problem.

Walt

Hay Guys

I was thinking of using Tip Seal as my stacks are quite old and water is seeping from various pores.

Any experience with it and its pro &cons and price.

Thanks & have a nice day.

I don't think you want to "seal" the blades unless structural integrity is a concern (i.e., "cracks"). Most hollow blades actually have "weep holes" at the ends to keep water from collecting inside which of couse upsets the balance of the set.

I don't think it's the blades themselves which are causing the noise (assuming they are all "pitched" the same).