Good Day All,

We recently re-installed a 400hp motor on a 177 Frick ammonia compressor that had broken rotor bars. After the cold alignment and sufficient warm up time we did a hot alignment check and found the alignment to be satisfactory. After the hot alignment check vibration data was taken to establish a new base line. We found a very high 120Hz exactly amplitude of .0358 “/per sec. We did a coast down and found the 2X disappeared as soon as power was removed. Our next step was going to be a motor current analysis but as learned in this forum, we first did a “running alignment” check using the monitoring function of the vibration analyzer. When the last bolt was loosened the 2X Dropped to the floor (.001). Now I don’t know just how much air space is between a rotor and stator but it only took .005 “ to maintain that low 2X amplitude. We saved time and $$ doing the easy things first and as I have said before it is this forum and the wealth of knowledge I have to thank. Thanks to all that post!!
Noisemaker,

Noisemaker,

Good catch. Make a soft foot check with a dial indicator step one (sometimes it becomes step 6 or 8, too ). And don't forget runout.

Are you sure that the old motor really had broken bars?

Danny,

There were two broken rotor bars that were suggested by MCA and then confirmed by the rebuild shop. I can only hope the contractor did the run out and soft foot checks before releasing the machine but one never knows......
Thanks Danny

If by "contractor" you mean the motor shop, my experience is they don't do much except 'repair' the obvious. If a contractor installed the motor, they probably have no concept of "soft foot."

Using the 80/20 rule as a guideline, I expect that 80% of people who install or maintain motors do not have the knowledge or experience to diagnose or correct soft foot.

In spite of advances in technology, training, etc., I expect that in 80% of industrial plants, the state of maintenance is going backwards, not forwards, for a variety of reasons. At least that's what I see every day.