DEFECTIVE SAND CAST ALUMINUM IMPELLERS!... Not American Turbine ours are investment cast aluminum.
I got a call yesterday asking me about what is the minimum thickness at the wear ring skirt. I told him that for a sand cast impeller it should be at least .150" because the sand casting technique causes porosity and therefore the casting is not as strong as investment (lost wax) casting. When you use sand cast molds the molten metal hits the sand mold and generates a lot of gas and because the impeller has a lot of thin walls the gas cannot escape before the metal freezes.
The investment casting process creates a much denser metal therefore a stronger casting. The caller also said the wear ring skirt was only 1.0" long I told him the machinist probably didn't have much experience doing jet pump impellers. With only 1" long skirt you lose .060" of sealing surface.
I told him that the probable reason that the skirt was so short was that if they were machined [U]properly/U] that they would have been thinner maybe even cut through.
He said the impeller was cheap and that he had a "Joe Six Pack" pocket book I told him yes that I had been "there" and I would try to help him out (sometimes we have impellers that are cosmetic defects) and maybe we could find him a deal on a sturdy impeller. I hope he calls back, he was on a cell phone and the call dropped before I could get his name.