We have 2 Reineveld centrifuges that we use for drying corn starch. Lately, one of them has been experiencing high axial and vertical vibration levels. Normally, when we have an out of balance condition we will only see it horizontally, but now the axial and vertical are twice the amplitude (.35, all the way up to 1.0 IPS) than the horizontal. There is a 4x RPM spike vertically, but not axially. We are trying to rule everything out, so does anyone know what direction a machine like this would be vibrating if it was running through it's critical speed? The speed does vary several RPM's through it's cycle, and it is only rated for 750 RPM max, but we are running it at 780 to 790 RPM.

Mark K,

Typically, the vibration should increase in the same direction as the normal axis of vibration as the rotor enters the critical; in your case the horizontal direction. Given the type of machine and the speeds you discribe, I would doubt you are entering into the critical range.

Based on your description, looseness of the bearing(s) and or bearing support structure is highly suspect. This would include the bearing, bearing housing, and structure.

Could you give us a description of the machine train and support structure.