When the total number of stages of the self-balancing multi-stage pump impeller is even-numbered stages, theoretically, the axial forces cancel each other out and are completely balanced. However, due to the deviation of the geometrical dimensional accuracy and relative position accuracy of the runner part from the design when the runner components such as the impeller and the guide wheel are manufactured, there is inevitably a residual axial force of uncertain size and direction, which depends on the thrust bearing.
When the total number of impeller stages of the self-balancing multi-stage pump is an odd number of stages, because the number of impellers in the low-pressure section and the high-pressure section is different by one level, the condition of fully balancing the axial force is destroyed. Consider the following measures when designing:
(1) Set up thrust bearings, such as single-row radial thrust bearings or thrust disc (tile) bearings to withstand unidirectional unbalanced axial force;
(2) The first stage impeller adopts a double-suction impeller without axial force, and the use of this impeller form in the first stage is also conducive to improving the cavitation resistance of the pump
(3) The final stage impeller of the self-balancing multistage centrifugal pump adopts a double-ring ring with a balance hole or an impeller with back blades (secondary blades) to achieve the axial force balance of the entire rotor. In fact, the balance hole or the back blade is still 10-15% of the axial force is not balanced and still needs to be borne by the thrust bearing. Therefore, when the impeller is installed, the number of stages in the high-pressure section is more than that in the low-pressure section to reduce the bearing pressure at the end of the high-pressure zone and at the same time make the pump shaft in a state of tension.
