Design modification ensures axial position in multistage centrifugal pump rotors

摘要

In this article, mechanical engineer Rafael Ocampo presents a case study concerning a group of centrifugal feed water pumps that suffered successive rotor failures. He discusses how the problem was traced to the thrust collar and the subsequent design modification that has provided a simple but effective solution. Any multistage centrifugal pump will requite a balancing device in order to compensate the axial force arising from the pressure difference on the two sides of the impellers. Depending on the type of balancing device employed, a thrust bearing could be also required. The most universally used thrust bearing is the Kingsbury type, consisting of a thrust collar or plate fixed on the shaft and two sets of thrust pads tilting on rings fixed on the pump body. In order to make the repeated disassembly and assembly of the pump easy, a nut usually fixes the thrust collar position on the shaft. This threaded joint must support the whole axial force developed in all impellers, minus that part of the force absorbed by the balancing device.