vibration in high speed compressor

Hi, we have a kind of a Nouvo Pignone compressor. That it has two shafts (low and high speed). By a gearbox the speed of high speed shaft reach to 12635RPM. It has journal bearings at both sides and proximity vibration probes measure the vibrations. Also I should say that the first resonance speed of that is about 9000RPM.

Recently, we've had high vibration at the high speed shaft, particularly at the opposite side of impeller. Vibrations are at 1X frequency (pictures are attached), therefore we suspected to unbalance and as we don't have high speed balance device in our region we had to balance the shaft at 1000RPM. But it didn't work and the vibration haven't gone. After that, we have balanced it with 3 different low speed devices for third times but we couldn't fix the problem. Also, we've checked bearings of the high speed shaft and we haven't seen any defects regarding the bearings.

Moreover, we don’t have any kind of considerable vibration on the shell or on the motor, and considering the phase analysis in high speed shaft, I should say that the angle is 60 to 65.  

I really appreciate anybody who tell us what we can do to mend it…


The pictures show radial vibrations at impeller side (5003a1, 5003a2) and the opposite side of that (5004a1, 5004a2) and their orbits with 1X filtration.  

 5003A15003A25004A15004A2orbit 5003orbit 5004


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