Balancing holes in single-suction centrifugal pumps are generally applied to attenuate the axial thrust caused by a pressure difference between the front side of a shroud and the rear side of a hub of an impeller. The magnetic drive pump, the subject of this study, has a leak-free airtight structure and an integrated structure of the impeller and inner magnet. To prevent the performance degradation of the magnetic drive caused by heat during operation, complex cooling flow paths connected to balancing holes have been designed so that a sufficient amount of coolant would flow around the magnetic drive. Due to this spatial characteristic, when balancing holes are applied to a magnetic drive pump, the balancing hole flow path becomes very long compared to that of balancing holes applied to conventional pumps. When the balancing hole flow path is long, the flow path loss increases, which in turn increases the adverse effect of balancing holes on the pump performance. Therefore, the design of highly efficient balancing holes to which a sufficient amount of coolant can be supplied is critical in a magnetic drive pump. To this end, two types of balancing holes were investigated in this study. First, balancing holes are drilled in the impeller that rotates during operation. Second, balancing holes are drilled in the inner shaft installed to maintain the centre of rotation of the impeller during pump operation. The results confirmed the flow characteristics of the two types of balancing holes and verified the effect of each balancing hole on the pump performance. Finally, this study found that drilling balancing holes in the shaft were appropriate for the magnetic drive pump, and this type can maintain relatively high efficiency and supply a sufficient amount of coolant to maintain the efficiency of the magnetic drive.
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