Abstract: A centrifugal pump incorporates multiple impellers which are driven by a shaft at constant speed. To engage an impeller, a ball end rod is operated, which interacts with an integral structure which comprises a disc, connector or a support collar, and face gear as linking means. The integral structure is further coupled with the impeller. During engagement, a linking means which is mounted on the impeller and also on the integral structure get coupled together resulting in engaging the impeller for rotation. The impellers can be engaged and disengaged according to the flow requirements thereby saving the energy.