A predictive maintenance department at a chemical plant was alarmed by a sudden increase in overall vibration values of their Wi-care™ system, installed on a ventilation fan for their production units.
The spectrum below is the spectrum at the moment the highest amplitude was reached.
The high peak shown above is at 8 orders or 380Hz with an amplitude of 7.6 mm/s.
The following cascade plot shows clearly that all the increased energy is purely coming from this 8 order peak.
What is the reason for this 8 order peak? This is a fan with 8 blades. 8 orders is the blade pass frequency.
This is was a fan that needs cleaning on a regular basis. The cleaning is done over a weekend with water under pressure. During the cleaning procedure, maintenance personnel must open a fan at the bottom of the fan house to allow the cleaning water to leave the installation.
In this particular case, they forgot to open the fan, and the fan house was full with water when the fan was started. The fan turned on, and acted as a pump. This was identified as a result of the alarm generated by the Wi-care™ condition monitoring system.
After opening the valve and removing the water, the fan was running again in smooth conditions.
The following cascade plot (3D Waterfall) shows the spectrum before, during and after.
Where there has been a significant, immediate change in operating parameters, overall vibration serves as a useful alarm system that calls for further investigation.
Utilising condition monitoring technology that includes both overall vibration alarms and high-resolution vibration spectrum analysis, ensures that the cause of the alarm can be quickly and accurately identified, and specific follow-up actions can be scheduled.