"Balancing Tip
When balancing fans, it is always better to use an outer section of the fan for a reference. This gives great results for balance due to refined placement accuracy of weight, but that is not always a usable choice.

Many times fans have too many surface irregularities that interfere with the reference strobe causing 2, 3, and 4 times running speeds to show up on the balance equipment.

Most often the best luck is found on the shaft, since this environment is more easily controlled. When this occurs, your actual placement of weights is often slightly off from where the balancing equipment expects placement. After initial test weight has been applied, interrupt the balancing equipment.

Your trim weight has now been calculated for you, and you have seen the fan wheel reaction to the additional weight during the trial run. You can then add trim weight according to what you feel is optimal placement. After a few runs the learning curve becomes easier.

This provides much better results and is often faster. Following final weight placements, the balancing equipment should have recorded the results allowing any follow up to be done as in the past."

In 16 years I have balanced literally hundreds of fans, of all different sizes, weights, and condition. After having said that I have some experiance in the craft, I need someone to explain what this tip is saying. I am completely lost.
I am not knocking the gentleman who posted it (he got a coffee cup for his hint), I'm just trying to figure out what the hint is.

I will sometimes take the box'x suggestion for a correction weight, put it where it says to, and then back up and tell the box that it is the trial weight. This allows the box to give a much closer calculation. At first, I thought that was what the hint was, but now I'm not so sure.
Any ideas?

Dave

Dave,

I don't get it either. Is he saying to put the balance weights on the shaft? Don't you have to use some pretty big weights there?

After reading it through a couple of times, I think the message is to put the "reference strobe" on the shaft, not on the fan blade. By "reference strobe" I presume he is referring to the reflective tape and photo-tach, or whatever system is used for the shaft reference. He then says that the trial weight may be difficult to place accurately (relative to the reference position), and goes on to suggest that this lack of accuracy can be compensated for by watching how the fan reacts to the trial, and developing a feel for the optimal placement of the trim weight.


At least, that's how I read it.

This excerpt is phenomenal
"Your trim weight has now been calculated for you, and you have seen the fan wheel reaction to the additional weight during the trial run. You can then add trim weight according to what you feel is optimal placement. After a few runs the learning curve becomes easier. "

Does somebody edit these "reliability tips"?

David

I think what he means is take your phase data using a reference mark that is outside the fan housing. I pretty much always do this because it's usually not safe to have your tach "looking" at the fan wheel when it's running, right? I do try and put my tape on the largest diameter that I can get to with the tach because I think it gives you a little more measurement accuracy (but maybe not), and it gives you better weight placement accuracy.

"When this occurs, your actual placement of weights is often slightly off from where the balancing equipment expects placement." I think what he means is with an 'external' phase reference, you will be off a little when you place the weight on the wheel, inside the housing, because you're trying to visually align two points that may be some distance apart. But I always mark the shaft externally where I want to place the trial weight, then align this mark with a reference point (bearing split line, housing split line, etc) so I can 'find' the position inside the fan.

"After initial test weight has been applied, interrupt the balancing equipment. Your trim weight has now been calculated for you, and you have seen the fan wheel reaction to the additional weight during the trial run. You can then add trim weight according to what you feel is optimal placement. After a few runs the learning curve becomes easier." I think this means he's sort of guessing at this point, or just balancing intuitively, without using his meter.

When I place my trial weight, I always tell the meter it is at "zero" degrees, regardless of where it is. The balance solution then gives a 'relative' solution, relative to the position of the trial weight. (i.e., 20 degs. means +20 degs from the current trial weight position; 340 degrees means +340, or more simply, -20 degs.) On every trial run, I say the weight is at zero degrees, and the solution is always relative to the existing weight position, regardless of how many trial runs I've made, or where the external phase reference is. This way, after your first trial weight, you don't even have to look at your original, external reference mark.

When I'm done, I carefully measure the position of the final weight placement and enter this into the meter using the 'edit data' function to document the actual final weight position.

I think Ian, David_G, Joe, & I were all preparing a response at the same time....and posted without benefit of seeing the others' post. Hence the apparent redundancy.

Since he mentioned a strobe, I'm guessing he's saying if you shot the fan outer section with the strobe light to determine your weight placement you would be identifying the actual spot for the weight. But, he says the irregularities in the fan surface can make this hard to distinguish . He's contending that by using the strobe light at the end of the shaft, where the surface is smooth you'd locate the weight location at the end of the shaft but then some error would occur when you moved from the spot on the end of the shaft to the actual weight location on the wheel. I'm not sure where the tip lies either but I think this is what he means.

Of course, as said many times on this forum, this is just my opinion but I could be totally wrong.

It's been a long, long, long time since I used a strobe light for balancing but as best I can remember we would mark clock locations on the end of the shaft and in the balance process would freeze the shaft with the strobe and note the position at 12:00 and this would act as a reference as to where to place the trim weight. How old is this article? If I had to go back to the old strobe light method I'd shoot myself.

Thank you all for your replies, and apparent confusion also.
It is good to see that being over 50 doesn't necessarily mean you can't understand anymore

Joe, I have to agree, if I had to go back to the strobe I don't know what I'd do. Although I have one as a 4th back up (have 3 lasers), I don't have anymore polar charts with a hole in the middle . Guess I'd have to use the keyway with a split line

Rusty, I too use the relative position deal. Just seemed to make things easier way back when Randy Fox was jumping around in front of the class teaching how to use the strobe and "electric eye".

Thanks again. I'm still not sure what he was trying to say.

D

It seems as though I have confused you all a bit. For the record, my tip was not edited. I take full blame for the confusion. My goal was to include as much information as possible, in a short entry. It didn't present itself as I had planned.

In my experience, when performing a fan balance, the best possible placement for the reflective tape is near the placement zone of the correction weights. On old dirty fans (which I do a lot of), if you are able to get the tape to stick, there is usually a poor surface for the "speed reference system" to read. When this happens, your 1x results can fluctuate and will even indicate 2, 3, and 4 times running speed. I simply meant to move the reflective tape to the shaft (belt drive applications) near the bearing. I don't recommend the end of the shaft though, perpendicular to the shaft near the bearing works well. The shaft is usually free of scratches and debris found on fan wheels and can be cleaned easily. Most of the time, there is a key way in the shaft. If you stick the tape next to the keyway, you can avoid the double reference. My equipment is very sensitive to scratches and lumps. For the sake of my equipment, I also prefer to have the "speed reference system" out of the air stream. Besides it coming loose and being chewed up, this will aid in poor readings from turbulent air flow (I have to balance fans that produce 150,000 CFM and up, this is a challenge when placing the reflective tape and tach). At this point it makes you want to use the old fashion strobe light, which can be easier. If you know the lag angle of the fan from previous job notes, you can make a quick educated guess as well. (Many brands of wheels paired with matching model #'s have similar lag angles due to manufacturing.) A lot of fans also give you the ability to balance at fixed points. When you used fixed points, the shaft reference does not always line up to your weight application points. Your weight placement as calculated by your balancing equipment is not applied as accurately as it could be. You will see the phase movement on your screen, and it may not have moved as close to target as it could have. This is when you can adjust the placement and amount of weight. If you let the balancing equipment recalculate, sometimes it will add to the opposite side or begin circling the fan wheel. You are no longer balancing efficiently at this point. Rusty stated "This way, after your first trial weight, you don't even have to look at your original, external reference mark." I agree completely. You are only adjusting; there is no longer a need for the beginning reference. Your amplitude and phase change will tell you the rest. IanS seems to have had similar experience as well.

Sorry for the confusion, I did not want to submit something this long, most folks quit reading early on when they see a page worth.

Jake

Jake, whenever I write something for "others" to read (except on this board where I shoot from the hip way too much), I edit, edit, and then edit some more. I may spend an hour editing and rewriting a single page report. I was taught in high school to "make every word count" and "there is a best way to say anything". (I shoot for that, but usually don't hit that mark.)

If I am submitting a major report, I always "sleep on it"... it looks a lot different the next day. I usually see lots of things that could be better said, usually in many fewer words.

No one should not share their knowledge because of concerns about writing skills, not being clear, or coming across wrong. That said, when we write, submit, or post something - especially for publication - it's out there, and we usually can't get it back. It will make an impression, good, bad, or indifferent.

Thanks Rusty, this has been a learning experience.

Jake,
I think I understand what you were trying to say now. However, do you actually try to put tape on the fan wheel itself, and have the access open during the balancing?
I have always used the shaft. I also use an angle indicator, which I can put on the shaft and on the fan wheel.
I guess I've never tried to out guess my box. I have learned to trust it, but I also understand that I have to be accurate with my weight and placement in order to balance in a couple of runs.
If I've done it before, and they haven't changed the stiffness, I'll get it on the "trial" run.
Sorry I couldn't understand what the tip was.

Dave