Mechanism analysis of double helical balance drum to improve axial force of multistage pump

Abstract

In the case of high pressure, the size of the multistage pump axial force sometimes reaches hundreds of tons, the seriousness of the problem generated by excessive axial force has surpassed the efficiency, wear and other factors, and has become a decisive factor in the stable operation of multistage pumps. In this paper, the 11-stage double-case multistage pump is taken as the research object. On the basis of studying the clearance internal flow mechanism, according to the pressure difference equation of axial motion of clearance fluid, the main factors affecting the balance force of the balance drum are analyzed, and a new type of balance drum — “double helical balance drum” is proposed, which is compared with the smooth balance drum in the hydraulic performance and axial force performance. The research shows that with the increase of the axial displacement of the balance clearance, the pressure drop between the clearances decreases linearly. Compared with the smooth balance drum, the pressure drop at the inlet and outlet of the helical balance drum is 1.30 times that of the smooth balance drum under the design flow rate condition, the mean velocity, mean velocity curl and velocity coefficient of the double helical balance drum increase, indicating that adding double helix can increase the dynamic pressure ratio of clearance fluid. In addition, the test results show that the head and efficiency of the double helical balance drum of multistage pump is increased by 0.76% and 1.1%, respectively, compared with the smooth balance drum, and the vibration amplitude of the front and rear bearing is reduced by 3.36%, 0.76% and 1.75% on average along the axial, radial and tangential direction. In addition, the temperature of the front and rear bearing is reduced by 3.1% and 8.7%, respectively, indicating that the double helical balance drum can effectively improve the hydraulic performance and axial force performance of the multistage pump at design operating point. The results of the study can provide reference for the long-cycle stable operation of multistage pumps and the optimization of balance drum design.