“Introduction:
IT IS JUST UNBALANCE!

Our Fan’s High Vibration Levels Are Due To Dirt Build Up! This Is Just The Way That This Fan Has Worked For Years Therefore It Must Be Normal!
SOUND FAMILIAR?

It is very common to find large ID and FD systems operating with high vibration levels. Since the predominant vibration frequency component is at 1xrpm, the root cause of the excessive vibration levels is often automatically attributed to unbalance and “dirty” air quality. Many large fan systems operate with continuously excessive vibration levels for many years (sometimes for decades) and experience continual fan system failures. In some cases, the fan systems experience failures every 2 – 3 months on sensitive components such as the variable coupling systems and bearings.

Unfortunately, owners continue to rebuild the fan systems and the associated coupling systems, as well as continue to clean the fan and balance the fan in an attempt to control the excessive vibration levels at a significant cost. The maintenance and loss of production costs are sometimes staggering. In a recent case, the owner lost over $4,000,000.00 in the first 6 months of a new large fan installation due to continual system failures as a result of excessive vibration levels.

 The OEM and several vibration consultants continued to deny the possible presence of a rotor critical speed. In another recent case, the owner had to continually shutdown the plant just to balance a hot large ID fan over many years. Just to enter the fan, there was a 48 hour cool down period and a minimum 12 hour heat up period during the startup. Over many years, the loss production costs were significant. The unfortunate part is that owners often resign themselves into believing that this is normal and they must just live with the problem!

Lastly, and more importantly, large fans typically fail in a catastrophic manner which can jeopardize worker’ safety. In one case when the fan failed, the blades went through the fan casing and the adjacent building walls and then continued to plummet down seven floors to the ground. Fortunately, no one was in the way of the exploding fan at the time of the failure; however, the plant union refused to have their workers near the fan citing safety concerns.

In many cases, the root cause of the excessive vibration levels is not unbalance even though the predominant vibration frequency component is at 1xrpm, but rather is an excitation of a fan rotor critical speed which causes amplified rotor vibration as well as unstable vibration operating conditions.”