New Shaft - Balancing Required?

The shaft is probably not the issue since I would assume that the diameter is not all that great and that it is pretty much machined symmetrically except for a key way or two.It is the wear and erosion of the old impeller mounted on the new shaft that I would worry about. If it is a new impeller the manufacturer should have balanced it before he shipped it but it is always a good idea to double check the balance on the new assembly combination especially at the 3500-3600 RPM range. Saves a lot on bearings and casings in the long run.

Stitch in time saves nine.

the coupling that is attached to the shaft and motor need to be balanced.

If you are using balanced, existing parts and only the shaft is new, no balancing should be required.

I would question whether the "existing" parts are still in balance. We do not know what service this pump was in. If it was at all corrosive or erosive the impeller and/or wear rings may not be in the same balance as when originally installed. That is why I would perform some amount of balancing, whether static or dynamic, depending on what he has available. After all, why did he need a new shaft in the first place? Whatever caused the need of a new shaft could have created other issues which could very well have affected the overall balance.

I know this could be a big mistake on my part, but I'm giving the OP the benefit of the doubt and assuming that no damage has occured to the existing parts.

Your point about not knowing the details is well taken.

I worked at an OEM PCB fabrication equipment manufacturer as Engineering Manager in the early '90s. We built our own impellers from corrosion resistant steel, titanium and Hasteloy C276. We ran our pumps at 3450RPM and rarely had a balance problem. When we did have one, it was obvious.

I see no reason to not at least static balance it, but the OP may.

Cheers.

You have not said any mistake, your advice is highly appreciated

Thanks for comment and advice, pump is manufactured by Wernert used in caustic process, and old shaft was badly worn out at Mechanical seal area, impeller also get worn out from back side, mechanical seal also was badly damaged, so we have fabricated new shaft and replaced the impeller and Mechanical seal..bearing found in good condition, it seem that pump was running dry..this is all about the failure. On other hand casing is cracked material is UHMW-PE, it was repaired several time by build up but it did not help, I am not sure if you have experience repairing this kind of material. thanks again