Hi all
Having problems with information regarding the clearence on one of our big id fans.There is about two inches of space between the wheel and the cone on this unit.As i understand this con should be inside the wheel to work at peak performance. My question in general is what effects might i see from this arrangement.
My limited balance experience is not good enough to argue my case with the powers that be.Any help would be greatly appreciated on this matter as i know from reading this board we have a lot of good balance people out there who probably have seen this before thank you to any and all who can help.

Lee, if I understand correctly, there is a 2" gap between the cone and the edge of the wheel (inlet)? What type of fan is this? Center-hung centrifugal, overhung centrifugal, axial flow (vane axial)??

I believe you will probably get some "recirculation" from the discharge back to the inlet which may make for "noisy" flow. You may see some broadband energy at the lower frequencies, with a raised noise floor. But as long as your 1x phase and amplitude are fairly steady, this shouldn't affect your ability to balance this fan. But it certainly is not an efficient setup for a fan.

Ok it is an overhung fan centrifugal.Phase readings where not stable.this unit came in as a rebuild. it had correction weights all around the wheel.More than what was on the old wheel we balanced quite a few times.i chased it and so did my partner.Next move is to strip it(which I would have done if it was all my decision.)Mostly I am curios as to what effects a fan not in balance and the fact that it is not set-up as in the wheel to cone alignment will have on balancing and what i would see in the vibration readings with regards to the air turbulence created by this gap.I would suspect laminar flow will be very bad and we have seen before a puffing of the fan housing and duct work. Production says they are seeing performance issues since the change out. thanks again lee

2", I never saw a gap that big. We always install overhung fan impeller as close as possible. Let's say, for a 4 feet wheel, we bring it to 1/8" when the wobble permit it. A wheel with correction weights all around is what you see when unbalance is not the only problem, when phase readings are not stable. As you probably know, without stable phases readings, you waste your time trying to balance.
Rusty bring you good point to check and I would add that with inlet problem you can also have 1X problem (and outlet problem will raise fan blades frequency).
Before attempt to balance be sure to have the basics, stable phase readings and near of 90 degres between vertical and horizontal phase readings.
You said that production noticed performance changes, I believe that that's the key you are looking for.
J-Marc

The sucking around the edge is more of a cushing effect with lost production or.......

Some will set the wheel in the cone or shroud a 1/2" or so.

With your readings and characteristics I would check and correct bearing to shaft misalignment and bearing to bearing misalignment and drive to driven misalignment and balance. I think it will be that simple once you've correct the mechanical flaws.