Steel thermally expands and contracts. As we learn in physics, a steel increases its length when heated. This expansion depends on the coefficient of thermal expansion of that particular material, some materials expand more than the other. Understanding the effect of thermal expansion is essential in centrifugal pump design.
A shaft of a centrifugal pump is typically made of steel and would experience thermal growth when the pump is in service. How much a shaft expand can be estimated beforehand. This change in length is proportional to the original shaft length. As this shaft expansion can jeopardize centrifugal pump reliability it is necessary to prevent its disastrous effect by giving some allowance for the thermal growth. Hence, the design of centrifugal pump incorporates the thermal growth factor.
For a centrifugal pump using a two bearing system, one bearing is fixed while the other bearing is not. By not fixing this one bearing, the effect of thermal growth on the shaft can be compensated by allowing this bearing free to slide. This thermal growth will not be perceptible to our eyes. We cannot detect thermal growth by just looking at the running centrifugal pump. However, the adverse effect of thermal expansion is real and it manifests itself in various problems affecting the centrifugal pump.