At what point should I get my fan balanced?

A basic rule of thumb for standard industrial fans is when vibration levels reach 0.2 in/sec peak velocity filtered. Always refer to oem literature for your particular equipment.

My fan has been balanced but is still shaking. Why?

Although unbalance is a common cause of excessive rotating machinery vibration, it is by no means the only cause. Vibration analysis will help identify causes such as misalignment, mechanical looseness, soft foot condition, and others.

Can I speed up my fan?

Fan speed should never be increased without confirming that the design speed will not be exceeded. When applicable, the v-belt drive service factor must be checked. The motor must also be checked for suitability to handle the new load. The rotor will likely require a trim balance to restore the balance tolerance for the new speed.

Why does my vfd controlled fan run rough at certain speeds?

For a situation in which unbalance is a primary fault, a fan will run worse as speed increases, since unbalance force is proportional to the square of the rpm. However, sometimes a fan will smooth out again as speed increases. This is a sign of a resonance condition in the system. Vibration analysis can be used to identify resonance frequencies so that the vfd may be programed to avoid prolonged operation at resonant speeds.

How can I reduce the energy consumption of my fan?

Slow it down. According to fan laws, power is proportional to the cube of the speed, so even a small change in speed can have a significant effect.

My fan is free-wheeling. Do I need to install a back-stop device?

Free-wheeling is air flow induced rotation of the fan rotor with the power off. It’s usually not a problem – unless the free-wheeling is opposite the fan running rotation and high speed. In such case, when the fan is turned on the motor has to work hard to overcome the inertia and get the motor spinning in the proper direction. A back-stop device installed on the rotating element will eliminate free-wheeling in the opposite direction when the fan is not running.

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DISCLAIMER – This information herein is provided as a reference only, and is not intended as a substitute for information provided by the original equipment manufacturers. JDM is not responsible for the use of the information herein and accepts no claim for issues of warranty, performance, or liability as a result of the use of this information.

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