Study On Effect Of Balance Hole Leakage On Characteristics Of Axial Force In Centrifugal Pump

The double seal ring impeller with the balance hole had characteristics of the ability to balance most of the axial force,it was still widely used in centrifugal pump.The liquid leakage played a decisive role in balancing the axial force for the double seal ring impeller with the balance hole.This not only affected the volumetric efficiency of the pump,the wheel loss and the pressure distribution in the pump chamber,but also had a greater impact on the calculation of the axial force,therefore,it was necessary to study the measurement and calculation method of liquid leakage in balance hole of centrifugal pump.In this paper,a special testing device was designed to measure the leakage of liquid in the balance hole by adjusting the liquid pressure of the balance chamber.Combined with the methods of experimental measurement and numerical analysis to test the balance hole liquid leakage,pump performance,pump chamber and balance chamber liquid pressure of the testing pump with different balance hole diameters.The characteristics of liquid leakage and leakage coefficient of balance hole and its influence on pump performance,pump chamber pressure distribution and axial force of balance chamber were depth studied.The main contents of this paper were as follows:1.Aiming at the problem of the influence of the balance hole diameters on the pump performance,IS80-50-315 centrifugal pump as the research object,and balance hole sets were designed to change the balance the hole diameters on the same impeller.The flow rate,inlet pressure,outlet pressure,rotational speed and shaft power of the testing pump with different balance hole diameters and different operating conditions were measured.The performance curves of the testing pump with different balance hole diameters and different working conditions were obtained.The experimental data showed that the performance curves of the test pump was similar to the different balance hole diameters.Increasing the diameters of the balance hole can affect the performance of the pump,it would make the pump head reduced,the input power increased and the pump efficiency reduced.When the diameters of the balance hole was less than 6 mm,the change of the diameters of the balance hole had little effect on the pump performance.When the diameters of the balance hole was larger than 6 mm,the change of the diameters of the balance hole had a great influence on the pump performance.Under the same pump head,the maximum difference between the inlet pressures of the pump was only 2.12 kPa,which showed that the pore size of the balance hole had little effect on the inlet liquid pressure.2.Aiming at the problem of measuring the actual leakage of balance hole,a test device was designed to measure the leakage of liquid in the balance hole by adjusting the liquid pressure of the equilibrium chamber,as the actual leakage of the balance hole is difficult to measure.The leakage of different diameters balance holes under different operating flow rates was measured.The corresponding balance hole leakage coefficient was obtained,and the dimensionless specific area and head coefficient was introduced.The experimental results showed that the variation of liquid the leakage and the leakage coefficient of the balance hole and the specific area had obvious regularity,When the balance hole diameters and specific area was increased,the liquid leakage of the balance hole increased and the flow coefficient decreased.Under the same specific area,the leakage of the balance hole liquid increases and the leakage coefficient decreased with the head coefficient increases.The cures of the flow coefficient and the specific area provided a new way to calculate the leakage of the balance hole of the similar pump.3.In order to study the axial force of the balance chamber region,the liquid pressure of the testing pump chamber under different working conditions was measured.Based on the uniform distribution of the liquid pressure in the balance chamber,the axial force and the axial force coefficient of the balance chamber region under different working conditions were calculated.The experimental results showed that the axial force of the balance chamber increased with the increase of pump head under the same balance hole diameters.The axial force of the balance chamber reduced obviously with the increase of the balance hole diameters in the same pump head,but the decreases of the axial force of the balance chamber were narrowed when the diameters of the balance hole increased.The curves of the axial force coefficient and the 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 between 2.5 and 4.5,the curves tended to be flat.When the specific area more than 4.5,the curves of axial force coefficient were almost parallel to the abscissa.4.In this paper,the model of the testing pump was used to calculate the whole flow path model of the test pump by establishing 45 calculation models of the model pump with different balance hole diameters and different flow rate.The experimental results showed that the balance hole leakage and the axial force of the balance chamber were obtained under different operating conditions,as well as the liquid velocity and pressure distribution in the vicinity of the balance hole and the balance chamber.The results are compared with the experimental values,and finding that the experimental value and the simulated value of the fluid leakage of the balance hole were gradually decreased with the increase of the flow rate under the same balance hole diameters.The balance chamber axial force gradually reduced with the increases of impeller balance hole diameters in same operating flow conditions.The existence of the balance hole made the balance chamber pressure lower,but the use of the balance hole made the pressure distribution at the inlet of the blade became confusing,the low pressure area on the back of the blade increased.The flow velocity of the liquid through the balance hole increased with the decrease of the balance hole diameters.