bobhousejr1
Mechanical
- Aug 9, 2006
- 3
We are having problems with ammonia screw compressors failing when the vibration data appears to be OK. If on a 3600 RPM compressor the lobe pass frequecy is 14,400 cpm (4X turning speed) then 3X this would be 43,200 cpm. We usually have no way of knowing what bearings are in the compressors but we assume the 1st inner race defect frequency to be about 5.5 to 6.5 orders. On most equipment we find that going out to 5X inner race frequncy will provide sufficient data to catch any problems. In this case that would be 117,000 cpm. There are no gears in these compressors. Is there any reason to go out any further on the frequency spectrum? If so what kinds of problems occur at these higher frequencies that would cause a catastrophic failure? Also, there are times when we see increased non synchronous energy between the lobe pass frequencies. We assume that there may be a bearing problem but when we check it again 3 months later this nonsynchronous vibration has gone away but there has been no repairs made. We are carefull to take all sets of data at 100% load. What could be going on? By the way, we have also successfully disgnosed bearing problems using this nonsynchronous energy between the lobe pass frequency. Thanks for your help.
