Analysis of liquid flow and axial force calculation in axial clearance for floating impeller of centrifugal pump

Abstract: Axial thrust balancing device is an important component for centrifugal pump stable operations. In special, the impeller which arranged in the same direction for segmental type pump and high head submerged (oil) pump is able to bring prodigious axial force .If excessive axial force exist in pump, it will cause safe accident, and influence work, and result in enormous economic expense. The floating impeller which integrated balance holes and the balance disc together is a new technology of balancing axial force automatically in the centrifugal pump. This technology has been applied in individual pumps with a significant and feasible effect, but it is still in its infancy which mainly concentrated on the introduction of principle and structure. In order to investigate the relationship of the fluid leakage, fluid pressure and the axial force on the stainless steel disc under different axial displacement, the flow characteristics in the radial and axial clearance on the back cover plate of floating impeller were analyzed. Fluid flow in radial clearance was simplified as viscous laminar flow of parallel plate model, and the fluid flow in axial clearance was simplified as 2D axisymmetric viscous laminar flow. Due to the equality the fluid leakage in radial and axial clearance, the mathematical expression of the fluid leakage, the fluid pressure and the axial force on the stainless steel disc in the axial clearance were obtained. The curves of the fluid leakage and the axial force on the stainless steel disc with the axial clearance were drawn by the calculation of the design example. The curves showed that the fluid leakage increased and the axial force on the stainless steel disc decreased with the increase of axial clearance, and these curves were relatively flat when the axial clearance was above 0.8 mm. From the perspective of reducing leakage, the smaller the axial clearance, the better. But a small axial clearance would cause the sharp variation of the lubrication and the cooling condition in axial clearance, and sintering phenomenon between the stainless steel plate and graphite disc. Therefore, in order to control the fluid leakage and reduce the axial force, the appropriate axial clearance was from 0.4 to 0.8mm. When stainless steel disc and graphite disc were uninstalled in the centrifugal pump, the axial force in the balance cavity was calculated. According to the comparative analysis, the floating impeller could obviously reduce the axial force. This research provides a reference for the study of floating impeller in centrifugal pumps.