What is critical speed of centrifugal pump?

For this point, it is important to note that any object made from an elastic material (and metal is an elastic material) has a natural period of vibration. This happens because the pump rotating assembly is not absolutely uniform around the center line of the shaft. So it is common that getting variations in the density of the materials as well as manufacturing tolerances and casting irregularities contributing to the problem. This eccentricity produces deflection when the rotating assembly rotates at the speed the centrifugal force exceeds the elastic restoring forces. At this speed the assembly will vibrate as if it were unbalanced, and could fail the seal, bearings or fatigue the shaft itself. The lowest speed at which this happens is called the first critical speed.