For upcoming plant, EPC contractor corrected angular misalignment for vertical pump motors by partial shimming (up to 0.25 mm). These are flange mounted motors of approx. 1 MW, 1000 RPM in hydrocarbon service. Shimming for flanged motor is acceptable / good practice ? Thanks in advance for members valuable comments.

I have personally faced such problems of angular misalignment in vertical pumps and aligned it by shimming between motor base and pump stool but it resulted in gap around the shims . The mating faces of the motor and stool were not in perfect contact with each other. The manufacturer (M/S Mather and Platt) forced us to remove the shims. The pump is still performing fine with 0.5 mm angular misalignment. Also in vertical pumps with guide bearings , the bearing clearance itself is around 0.3 -0.4 mm. How we can expect to achieve angular alignment around 0.05 mm? If you really want to go for alignment, you may try blue matching between motor base and pump stool(a very time consuming process). But a big but is there. Yet, in another pump (CEP) of around 1MWe , we have put shims for correction of angular misalignment and this pump is also performing fine. A lot of contradictions. Consult OEM also. Pl. tell the make, model , HP and if possible, a sketch of the same.
Regards.

I'm not real comfortable shimming face mounted motors for a couple of reasons.

1 - Many of the machine problems I've lived thru (and sometimes caused) have been related to not-so-hot (flexible, incomplete) machinery mounting.
2 - My first "rule" is each anchor bolt should be hard shimmed. This one is achievable on a face mounted motor.
3 - My second rule is shimming should provide neutral support. On a face mounted motor this means the shims should vary in thickness at each bolt position, and in severe cases, on each side of each bolt.
4 - My third rule is a machine's support should follow the manufacturer's lead as to being continuous or having discreet locations or pads, but the design of some machines' supports sure seem to have originated with the custodian's grand-daughter who is very fond of Dr Seuss.
5 - My fifth rule is flexibility is my second best friend (next to ductility), but must be handled VERY carefully.

http://www.made-in-china.com/image/2f0j00rvyTuaRnVEczM/...e-Pump-Vertical-.jpg
http://www.sibul.com/images/VPMM%2004.JPG
http://img.alibaba.com/photo/52368277/Vertical_Hollow_S...r_Deep_Well_Pump.jpg
http://www.rainbird.com/images/products/turf/pumpstatio...tation_SEAsia_bg.jpg

Note on most of the motors in the above linx the anchor bolts are a long way from stiff vertical supports.
This means a shim under each bolt may not necessarily lift the entire motor flange equally, but induce a flexible local wave in the flange, or in extreme cases, be a bump in the rug and not change the alignment at all. The flexibility aspect has been used intentionally by some pump MFRs to de-tune reed frequency resonances.

Thanks AKHTAR and Dan Timberlake. We convinced our contractor to remove shims and alignment is still within tolerance. Your inputs reinforced our understanding..