Yesterday I tested a McQuay roof top air handler. The vibration at the outboard fan bearing was 3.4"/sec, at fan speed. I inspected the fan and structure for something broken and found nothing. In the process of turning the fan, I thought I heard water sloshing. I turned it a few more times and determined that a blade seemed to contain water. We drilled some small holes in the blade and the water came running out. Now the fan speed vibration is .27"/sec. Not a clue how the water entered this particular blade. The blade is a stainless steel air foil.

Yea, I had this issue on a 1500 hp induced draft fan. Balance weight calculation indicated over 10-lbs. I saw water weeping over the backing plate and had holes drilled into every (12) blade to be sure. It was easier to balance afterwards!

Walt

Perhaps at some point the fan was 'off' and maybe rainwater entered from the top and ran down onto (and into) the bottom blade? Anytime I have high imbalance on a fan I like to do a "rock down" test if possible to determine if there is an obvious heavy spot, and if so, I try and see why it might be heavy. On belt-driven fans, I drop the belts off if possible before doing this.

I have not seen water, but I have seen fly ash and coal dust inside foil type blades on ID/FD/PA fans on boilers. A bump test helped us to identify which blades were affected.

I've definitely seen water in air foil fan blades. I've seen it in cooling tower blades as well.