April 22, 2015
BASE BOUND, Is There a Way Out?
By Mac MacCormack
As any of the Vibralign trainers can attest, more often than not, when going out into the field on day two of a training class our clients want to perform a shaft alignment on their biggest challenge.
When conducting training at a Waste Water Treatment facility, the decision was made to perform a precision shaft alignment on a pump skid that was known to be base bound. The VibrAlign Alignment Blog has some very good information concerning base bound/ bolt bound situations and corrections. However, it can cause some major frustration if one does not know how to compensate for them
Although I was unable to take pictures of the pump/motor assembly, the following is how this situation panned out.
Using their newly purchased Fixturlaser NXA Pro, the initial alignment measurements were taken. I would like to note here that there was no looseness in the coupling. I suggested that would likely not be the case if the alignment was close.
Below are the initial results. As you can see, the motor was sitting substantially high at the center of the coupling (+56 mils) and with vertical angular misalignment of 19 times the acceptable angular tolerance of 1.0 mil/1” for 1200 RPM!
The alignment team set about to make a Verti-Zontal Compound Move and discovered a problem. There were no shims under the motor. So what are some possible solutions? One could remove the motor, cut the motor base from the pump skid, modify the base and re-weld it to the pump skid. Impractical but a possibility. One could shim the entire pump assembly, but that would also include modifying the piping. Also impractical but a possibility. Or one could use the Foot Lock function of the NXA Pro.
This particular pump assembly actually had an adjustable foot on the coupling end. It had also been replaced in the non-too distant past and there was a possibility that it may have been improperly installed to begin with.
Therefore the team began making the recommended adjustments as indicated below by the NXA Pro Foot Lock function.
Not only did they get out of a base bound condition, the assembly began to turn more freely as the coupling strain was relieved and it was determined that with the excessive looseness in the newly freed up coupling, a new coupling insert was in order.
After the vertical and horizontal corrections were made another set of measurements were taken with the following results of what began as a base bound condition.
Pretty good alignment for a 1200 rpm motor! Nice job gentlemen, not bad for a 30 minute precision shaft alignment!!!