How to balance the axial force
1. For small pumps where the thrust bearing does not have much axial force, we often use thrust ball bearings to balance the axial force. It is particularly reminded here that the installation of radial thrust bearings has direction requirements. If they are installed reversely, they will not be balanced. The axial force will cause the shaft to lose its positioning and cause the rotor to move, which can burn the motor in the slightest, and cause a major accident in the worst case. It must not be taken lightly.
2. The structure of the balance hole is to open several small holes axisymmetrically on the rear cover of the impeller near the wheel seat, so that the high pressure liquid at the rear cover returns to the inlet of the impeller, thereby reducing the pressure at the rear cover of the impeller. Balance the effect of axial force. This structure requires a sealing ring at the rear cover of the impeller, that is, it is not suitable for pumps without a sealing ring structure at the rear cover, because the leakage of the pump is large at this time and the head loss is serious. This structural balance ability is related to the number and size of the balance holes. Because we cannot calculate accurately, this method cannot completely balance the axial force, and there are still 10% 20% of the axial force that cannot be balanced. The total cross-sectional area of the balance hole is 3 to 6 times the annular cross-sectional area of the ring gap.
3. Double-suction impeller The double-suction impeller is a symmetrical structure, so it can balance the axial force.
Fourth, the back blade Back blade means that there are blade-like ribs on the rear cover (outside) of the impeller (some are curved like blades, and some are upright). It pumps the liquid behind the impeller like another impeller to make The liquid pressure at the rear cover is reduced, so as to achieve the purpose of balancing the axial force. The balance ability of this method is related to the gap between the impeller and the pump cover, the height of the back blade, and the length of the back blade. The larger the gap between the impeller and the pump cover, the worse the balance effect, and the smaller the gap, the better the balance effect. However, the design clearance is too small. Due to processing and assembly errors, it may cause friction or collision between the impeller and the pump cover, which will affect the operation. Generally, the value given in the design is the clearance 0.5~3mm, and the larger pump takes the larger value.
5. Symmetrical arrangement of impellers Multi-stage pumps have more impeller stages, so the axial force is greater. Sometimes the impellers are arranged symmetrically to make the axial forces generated by them cancel each other out, so as to achieve the purpose of smoothing the axial force. In fact, the double-suction impeller is a special symmetrically arranged impeller.
6. Balance drum and balance plate Balance drum and balance plate are devices used to balance axial force in multi-stage pumps, and are installed behind the final stage impeller. There are also two installations together.
