LOMAKIN AFFECT L018
Since operation off of the best efficiency point (BEP) is common with centrifugal pumps, you will be experiencing shaft loads well in excess of those discussed in critical speed calculations. This means that your critical speed will actually be experienced at a much lower rpm than expected.
The critical speed numbers normally used, reference a shaft running in air.
In actual practice the impeller and a major portion of the rotating assembly is immersed in liquid that provides a hydrodynamic support to help stabilize the assembly.
This hydrodynamic stabilizing force is referred to as the “Lomakin Effect”.