Experiment and analysis of balance hole liquid leakage in centrifugal pump

Abstract: Balancing and reducing the axial force is one of the most significant subjects in the research of the centrifugal pump. The most frequently-used method to balance the axial force is to use the double seal ring impeller with the balance hole the single-stage single-suction centrifugal pump. And the liquid leakage has a decisive role for the ability to balance the axial force of the double seal ring impeller with the balance hole. Therefore, it is indispensable to study the measurement and calculation method of liquid leakage in balance hole of centrifugal pump. Aiming at the problem that the actual liquid leakage of impeller balance hole is difficult to be measured, a special testing apparatus was designed by adjusting the liquid pressure of the balance chamber. Pump performance, balance hole liquid leakage and liquid pressure in the balance chamber was tested and analyzed when the diameters of balance hole were 4, 6, 8 and 11 mm. Some important test curves such as curves of axial force coefficient and specific area in different head coefficient and their variation characteristics were obtained by calculating and analyzing the experimental data. Results showed that when the diameters of balance hole were less than 6 mm, the diameter of balance hole had little change on the head, input power and efficiency of pump. Increasing the diameter of impeller balance hole would reduce the head and efficiency of pump and enlarge the input power. The pump inlet liquid pressure had a sharp reduction after the first stage of zero pressure with decreases of head in the same diameter of balance hole. The maximum difference between the pump inlet liquid pressures of different balance hole diameters were only 2.2 kPa in the same head, which showed that the diameter of balance hole had little effect on the pump inlet liquid pressure. The liquid leakage of the balance hole and the pressure of the balance chamber increased with the increase of the head. The liquid leakage increased significantly and the liquid pressure of balance chamber reduced significantly with increase of the diameter of balance hole in the same head. The axial force of the balance chamber increased with the increase of the head in the same diameter of balance hole. The axial force of the balance chamber reduced obviously with the increase of diameter of the balance hole in the same head, but the decreasing amplitude of axial force of the balance chamber decreased. The relational curves between the liquid leakage of balance hole and the specific area (the ratio of the total area of the balance hole to the clearance area of the rear seal ring) had obvious pattern, the balance hole leakage coefficient decreased with the increase of specific area in the same head coefficient. Under the same specific area, the larger head coefficient, the smaller leakage coefficient of the balance hole. The test curves of axial force coefficient and specific area were the non-linear curves, when the specific area under less than 2.5, the axial force coefficient decreased sharply with the increase of the specific area. When the specific area was between 2.5 and 4.5, the curves tended to be flat, and the mean value of axial force coefficient was 0.112. When the specific area was more than 4.5, the curves of axial force coefficient were almost parallel to the abscissa, and the mean value of axial force coefficient was 0.067. This study provides a new way to calculate accurately liquid leakage amount of the balance hole and axial force in the balance chamber region. It also has a great influence on the volumetric efficiency of the pump, the loss of the wheel resistance, the liquid pressure distribution in the pump chamber and the calculation of the axial force.