Hello One and all
Glad to see all the banter about fan balancing.This may be a newbie question or not but we have been in discussion as to what the damper settings should be on any particular fan that has dampers.Should the dampers be set to the operating settings when balancing or closed.I say they should be at the operating positions.I have more questions but will wait to see what the outcome of this post is before I ask anymore.

Lee,
The most important thing is to stay consistent. If you start with the dampers open, make sure they stay at that position through the balance. You can balance closed, but ensure they stay closed. I prefer to balance open at full load condition. If static pressure will build, open a relief on the discharge side, i.e. door, access cover, etc. Good luck.

Nicholas A. Martin

I was wondering if the closed damper position would create a stall condition or not and if so what other effects might be seen.I agree Nick,
being consistent is the key to alot of our techniques when it comes to predictive technologies.Thanks, Lee

Lee,
I have balanced with the dampers both opened and closed and agree with Nick, be consistent through out the balance job. I have noticed blade pass frequencies with the damper closed but you are filtering out everything but 1X while balancing. I have also noticed fans will heat up when ran for a while with no air moving through them. My preference is under normal operating conditions when possible.

Ronnie

Lee,

I too have done balancing both ways with good results. As Ronnie states, it is best to balance under normal operating conditions where possible. Many of my fan balances deem it almost impossible to do under normal load conditions due to excessive heat and material blow by. For most of my customers time is of the essence, and having to wait an hour for cool down for each balance run would be unacceptable. Therefore, the dampers are closed. Regards, Brian

Thanks Brian and Ron
It seems to be agreed that when in rome do as the romans do so that is what I will do.I am going to do a little more reading in the mean tine.I Have Art's second edition on mechanical vibe I refer to lots so Thanks for the responses they are always appreciated

Sorry Nick
forgot to thank you as well

Lee,
I am also agree with Every body's points and I just want to add a reminder that in case of probability of material deposits(e.g exhaust fans with dampers placed on the fan inlet line)it is recommended to have the dampers fully closed.

On some small shaft-mounted fans you have to remove the inlet cover to gain access to the fan. You need to replace the cover between runs so the fan is actually loaded. I balance a lot of these fans for a customer during shutdowns, and I'd never had a problem leaving the cover off while balancing. But this last time on one fan when I closed it up after balancing it, vibration went from 0.1 (balanced)to 0.6 in/sec (at 1x). The problem was the outboard motor bearing loose in the housing which didn't show up when the fan was unloaded. Had to replace the motor, but luckily the fan was still balanced.

So now I replace the inlet cover on each run.... takes a few extra minutes, but will save time in the long haul.

Rusty
I have always put things back to normal before making a run.The reason for this and it happened early in my balancing career was that while doing one particular job I had not one but two weights decide to release themselves and scare the livin bejeses out of me and those who where standing around gosh-hawking.You never know what is going to happen until it happens.Thanks for the reply Rusty

Many of our fans are hot air fans and we usually balance them during an outage. This means that they must pump cold air and most of the time they will not reach full speed (turbine driven units) or they will trip out on overload if we leave the dampers open. We have to close them to be able to run the fans. I agree with all that you should leave the dampers in the same position for the entire job.

Gary B