A small detail that is easily overlooked during assembly after pump repair.
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In a volute pump, the midline of the impeller outlet, that is, the midline of the width at the impeller outlet, should be aligned with the midline of the volute inlet. If there is misalignment, it should be adjusted by adding shims between the impeller hub and the shaft shoulder. The two centerlines should be kept within a range of 0.5 millimeters. For pumps with a high specific speed, the impact is slightly worse, but it has little effect on the pump’s performance. For pumps with medium to low specific speeds, since the outlet of the impeller is very narrow – for example, only 10 millimeters wide – any deviation of 1 millimeter from the midpoint of the volute has a significant impact on the pump’s performance. It is recommended that after adjustment, the error between the two centers (the impeller and the volute) be kept within 5% of the impeller’s outlet width. The same is true for guide vane multi-stage pumps, which are used to control the error between the midpoint at the impeller outlet and the midpoint at the guide vane inlet. For space vane pumps, it is best to use the data provided in the assembly drawings to determine the position of the impeller within the space vanes. If there are no drawings, the position of the impeller is adjusted based on experience or test results.
You are referring to the issue of axial alignment in multi-stage centrifugal pumps, right?
When servicing all centrifugal pumps and vortex pumps, attention must be paid to the alignment of the impeller flow channel and the pump outlet; otherwise, the pump’s efficiency will **decrease**.