Investigation of a Centrifugal Pump Stage With Radial Impeller and a Pump Stage With Small Stage Diameter

For radial multistage centrifugal pumps a combination of a radial exiting impeller, a vaned diffuser and a row of return guide vanes is used for each stage of the pump. Hence the inner diameter of the stage casing is much larger than the diameter of the impeller. In case when the space for installing the pump is limited, for example in case of submersible pumps, a high number of pump stages is necessary to produce a sufficient hydraulic head. Pump stages with an impeller diameter equal to the inner diameter of the casing can reduce the number of the stages, but up to now the efficiency of such pumps is lower than the one of a conventional pump. Improving the design of these pumps in order to increase efficiency, stationary diffusers were developed at the Institute for Turbomachinery and Fluid mechanics at TU Kaiserslautern. While the pump liquid cannot exit the impeller in radial direction, the hub diameter is reduced by the width of the impeller at the outer diameter. Hence the pump liquid now exits the impeller in axial direction. This design affects both the hydraulic and the rotor dynamic performance of the pump. Furthermore the axial thrust has dropped, because the flow and the allocation of static pressure in the impeller side spaces has changes compared to radial pump stages. In this paper results of measurements of vibration and axial thrust at radial centrifugal pump with four stages are compared with these of a four stage pump with small stage diameter. Furthermore the hydraulic datas of both designs a presented.