Balance method of pump axial force

1. Thrust bearing

For small pumps with low 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 balance the axial force. In addition, the shaft loses its positioning and causes the rotor to move, which may burn the motor in the slightest, and cause a major accident in the worst case. It must not be taken lightly.

2. Balance hole

This structure is to open several small holes axisymmetrically on the rear cover of the impeller near the wheel hub, 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 and achieving a balanced axial force. The role of. 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 at this time the leakage of the pump is large and the head loss is serious.

The balance ability of this structure 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% or 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

Because the double-suction impeller is a symmetrical structure, it can balance the axial force.

4.The dorsal blade

The 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 rear cover The liquid pressure is reduced, so as to achieve the purpose of balancing the axial force. The ability of this method to balance 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 gap is too small. Due to machining 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 gap 0.5~3mm, and the larger pump takes the larger value.

5.Symmetrically arrange the impeller

Because of the large number of impeller stages, multi-stage pumps have greater axial force. 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

The balance drum and the balance plate are both devices used to balance the axial force in the multi-stage pump and are installed behind the final stage impeller. There are also two installed together.