Fan Testing for Balance and Vibration
Fan testing for wheel balance and fan vibration testing are key to our quality assurance process because ignoring them can cause catastrophic failures in the field. So we take the testing process very seriously.
Diligent fan testing ensures that we can address these critical issues before we ship the fan. So what is diligent fan testing? For us, it includes:
- Dynamically balancing the wheel to ISO G6.3 minimum.
- Full-speed, mechanical run test performed on the fan assembly.
- Vibration analysis conducted at the fan’s operating speed.
- Vibration analysis during fan coast-down to detect any resonance.
- In-depth bearing analysis designed to detect any potential bearing problems.
Performance Testing for Wheel Balance
In a centrifugal fan, the axis of rotation is not actually connected to the weight center of the fan. When the two are not perfectly aligned, there is an imbalance in the fan.
Wheel balance is a function of fan rotor weight and the radial distance between the axis of rotation and the weight center. Wheel imbalance is important because it can be a major factor in fan vibration, or affect other components that contribute to vibration.
Our wheel balance testing looks for causes related to construction: structural mounting and support, corrosion or abrasion, material build-up, a bent shaft, or other component problems. Correcting for imbalance, or balancing: means we change the weighting to move the center of gravity back to the axis of rotation, bringing the fan into proper alignment.
Fan Vibration Testing
The causes of vibration fall into two main categories: mechanical and aerodynamic. Wheel imbalance falls within the former, and together with other loose components, comprises the most common culprit. But that does not mean that the other causes are uncommon.
While balance testing can occur without running the fan, other sources of vibration require an actual run test. For example, vibration from air flow arises when the vibration frequency is different from the speed of rotation, so we cannot identify them without run testing.
With the fan mounted on a rigid base to isolate the fan from external vibration during testing, vibration testing allows us to test for airflow issues as well as mechanical issues. If there is an air-flow-related problem, then increasing the air flow through the fan during testing will reduce or eliminate the vibration.
How to Avoid Fan Vibration in Your Application
Successful run tests do not mean the fan is impervious to vibration issues after installation. How you mount and support the fan in your actual application is also a major factor.
Ideally, we would install every fan on a solid and appropriately-sized concrete foundation with enough mass to withstand vibration frequencies from the fan and the surrounding environment. However, this is not always possible. Many applications don’t allow for enough space for such a foundation and many others are within steel mezzanine structures. In such cases, isolation will be necessary.
For more on vibration isolation not related to fan testing, check out our blog, Fan Vibration Isolation Considerations.