A Pump is the heart of most industrial systems. To make these systems as efficient as possible, the pump must be selected properly to match the requirements of the water source, the water piping system as well as the industrial equipment. There is a real need to look at the borehole pump behavior and to modify its design for the sake of improving its characteristics. In this research, a 1kW, three-stage, borehole pump was tested. Its impeller outer diameter was 11.7cm with radial and axial clearances of 2mm and 1mm, respectively. The impeller outer diameter was reduced to 11.3cm and then to 10.9cm, for the same pump casing. The radial clearance between the impeller outlet and the pump casing was changed consequently. Hence, three radial clearances were tested, namely; 2mm, 4mm and 6mm, respectively. These radial clearances corresponded to clearance-impeller radius ratios of 3.4%, 6.8% and 10.2%, respectively. The axial clearance, between the impeller outlet and the diffuser inlet, was varied three times, from 1mm to 2mm and then to 3mm corresponding to clearance-impeller width ratios of 16.6%, 33.33W and 50%, respectively.
The effect of varying the previously mentioned design parameters on the performance of borehole pumps was investigated. It aimed at getting the radial and axial clearance values corresponding to optimum pump performance. The results revealed that; changing either the radial or the axial clearances or both has a remarkable effect on the pump performance. Within the tested range, the optimum combination found was; to run the pump at discharge values above the corresponding values at the normal operating point, with radial and axial clearances of 6mm and 2mm respectively. This corresponds to a radial clearance to impeller radius ratio of 10.2% and axial clearance to impeller width ratio of 33.33%.