Pump alignment with Coulping installed?

[JonnyWill]

Hi all,
When performing laser alignment must the coupling be removed?
I’ve witnessed a millwright/mechanical fitter performing an alignment check on a pump with the coupling installed, however the coupling bolts are loose.
Will this not prestress the alignment? REMOVE COULPING !!
Cheers in advance.

 

[JJPellin]

Most laser systems are designed to perform the alignment with the equipment coupled up. It might be possible to do the alignment with the spacer out. But depending on the way the particular laser system takes the measurement, accuracy might be reduced. The main problem with performing an alignment with the coupling installed is that forces from the coupling could be holding a shaft up within the clearance of a sleeve bearing. We have seen this problem when the coupling was very stiff and the motor rotor was very light. For a certain class of equipment, we know ask the mechanic to remove the coupling spacer and recheck the alignment to be sure this is not occurring.