When looking at troubleshooting machinery running a process it can quickly follow the chicken and egg path.
What to look at first?
What is the originating problem?
Not knowing what the cause is and chasing a number of possible sources can become overwhelming. When working with a new engineer one day I saw this classic problem. He had an installation with vibration problems. He spoke to his mechanical group and they recommended a bearing overhaul. Then he went to the controls group and they thought it was a vibration sensor that needed to be changed.
After reviewing the filling control diagram we could see that on dewatering the vibration was increasing. This is not unlike the unbalance condition in your home washing machine. Too many towels and sneakers. The uneven cake is not as apparent when the liquid level is above the cake but much like your washing machine, the spin cycle will show the uneven loading.
Horizontal centrifuges and washing machines are not as prone to this problem as the force of gravity or 1G doesn’t affect the 200 in a washing machine or up to 1500Gs of rotation in an Inverting Centrifuge. Vertical centrifuges though are significantly impacted by 1G pulling the product to the bottom and therefore show much higher vibrations than a horizontal centrifuge.
However, it is possible to feed an Inverting Centrifuge too fast and this is what our new engineer was seeing. Upon reducing the flow rate we were able to have an even cake and avoid pulling the bearings or changing the vibration sensor.
We were able to bring the centrifuge back to “Zen” mode.