How To Align a “Moving” Motor.

After 34 years, aligning a few thousand machines, teaching millwright training for a technical college, and being an instructor for VibrAlign, I sometimes think that no alignment challenge can beat me!  Then something comes along to really put me in my place!

I was put in such a place while training at a large manufacturer in South Carolina.  This company has dozens of small utility pumps.  I will not name the pump manufacturer, and no photos will be used, but I will explain the set-up.  This machine was used for the “hands-on” portion of the training, since the company had been experiencing excessive vibration from the unit.

The pump assembly skid consists of two rails, which bolt to the floor.  This skid should normally be grouted, but this one was not.  Underneath the motor is a plate steel riser, approximately 1/8″ thick, and about 4 inches tall.  On top of this riser sat a 40 HP, rolled steel plate motor.  Rolled plate motors are not uncommon, but this was the largest horsepower motor I had seen using this type of motor construction.

The normal pre-alignments steps were completed, with a special emphasis on minimizing soft foot, since motors of this type do not have the typical four cast iron feet.  The motor housing is broken in a sheet metal brake to provide two long “feet”-one on each side of the motor.

The first alignment measurements were completed, and the motor was shimmed and moved to the values calculated using the Verti-Zontal method.  The 2nd set of result measurements were close, but not on target.  While performing live moves with the laser alignment tool, the mechanic leaned on the motor.  We noticed  movement at the coupling of over 10 mils (0.010″)!  So we stopped what we were doing, and checked every hold down bolt on the motor, riser, and base.  Everything was tight.  So, we checked again, and we still got over 10 mils of movement.

While we did not conduct any detailed study, due to time constraints, we could only assume the movement was due to insufficient stiffness of the frame, riser, and motor.  A recommendation was made to this facility to grout the base, and add some horizontal stiffening to the frame and riser.

So, how do you align a moving motor?  You do not.  You make modifications to the structure to make it rigid enough to be aligned.  If you do not, you are asking for problems.

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  1. Guruprasad on March 22, 2015 at 11:10 pm

    Dear sir
    We are having thermic fluid pump with motor coupled by spider( No:110).
    Last week we are chaiged the motor for servicing, now installed the pump but the motor droving more current as compared to previous. ( raised from 10 to 14).
    Please suggest me for perfect alignment.

    Thanks and Regards
    Primacy Industries

  2. Stan Riddle on March 23, 2015 at 12:55 pm

    Good alignment specifications are based more on running speed. At 3600 rpm, the optimal alignment would be .05mm offset, and an angularity of about 1mm/100mm, or .01/mm. But I would suggest that if you have changed the motor, a different motor may have more to do with your current increase than alignment. Different windings, bearings, stiffness, internal bearing alignment – all of these can influence current draw.

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