January 30, 2012
What’s Eating Your Couplings?
By Steve Matthews
If you are a regular Alignment Blog reader, you may remember an entry in which Stan Riddle discussed why we should care about precision alignment of flexible couplings. Today, I would like to offer up some evidence that many of you may well relate to. We were called to align this chilled water pump in a brand new chiller building. The pile of black rubber dust on the base is the coupling shredding itself toward failure. This machine had only been in service for a few weeks.
Here is the shaft alignment condition of the machine when we arrived “as found”:
Red icons indicate out of tolerance condition, based on 0.5 mils/inch angularity and 2.0 mils offset tolerance setting. Most notable however, is that while this data shows a very poorly aligned machine with respect to precision standards – the alignment is acceptable according to the “coupling tolerances”. The client wisely decided to realign the machine so they would not be frequently replacing these shredded coupling inserts.
The other notable data from this experience was from the vibration acceptance test. A testing company was hired by the owner to certify the new equipment installations met certain vibration acceptance criteria. The vibration acceptance test was performed on this machine in this misaligned conditioned, and found to be within the accepted limits. This is commonplace for this type of coupling – a significant misalignment can exist which deteriorates the coupling insert and places life-reducing forces on the machines – without creating significant vibration.
Just for the record, the following data shows the alignment upon completion, 19 minutes later: