A problem with a fan or an unforeseen shutdown can lead to severe consequences. A standstill of a fan often leads to a situation where the productivity of the workers and / or the quality of production decreases.
In the case of a fan in operation, it is possible to discover a dysfunction by listening to the produced sound and checking the vibrations of the fan. This does not guarantee a perfect working machine, but it is an effective method to find an existing problem.
Does the fan produce a different sound?
To check if the fan produces a different sound requires some experience because fans that are in a good state can produce loud noises too. But a technician who is familiar with the fan will more likely notice a change in the noise a fan makes, which can indicate a changed situation.
Mechanical noises are not in place with a well functioning fan. Grinding, whining or rattling noises indicate that the system isn’t in an optimal condition. Fluctuating noises are also a sign that the fan is operating at an unstable point in the air flow chart.
The bearings can be checked with a stethoscope. For an experienced person a simple steel bar can be sufficient. The less experienced technician can use the audio-CD that is included with the electronic stethoscope. On this CD, it is easy to hear the difference between well functioning bearings and bearings where something is amiss.
Is the fan subject to vibrations?
Here too, without a vibration meter it is possible to rely on the technicians experience even though feeling still is subjective. With a vibration meter the effective vibration values can be measured. It is recommended to perform this measurement as close as possible to the bearings on a solid spot, preferably in the 3 directions defined in the ISO 14694 standard.
A measurement performed on the fan casing is not relevant. Measuring in the 3 directions allows finding the error. An imbalance will only cause radial elevated vibration values, while a higher axial value can indicate an alignment error.
With a more sophisticated vibration meter, it is possible to measure a spectrum which can be important to detect the error. A vibration peak at 1 time the rotation frequency can be caused by an imbalance or by a natural frequency. An extra small peak on 2 times the rotation frequency can be caused by an eccentric bearing while a large peak on 2 or 3 times the rotation frequency can indicate bad belts or an alignment error. More information is available in the ISO 14964 standard.