It's important not to open the balance hole too much, as it can significantly affect the pump's efficiency. This section will explain some common methods for balancing axial thrust in centrifugal pumps.

In single-stage pumps, there are several typical ways to manage axial forces:

1. **Balancing Hole**
A balancing hole is created near the hub of the rear impeller cover, and a seal ring is installed on the same area. The outer diameter of the seal ring matches that of the impeller's suction inlet. When the pump is operating, the liquid behind the cover is connected to the suction port, resulting in similar pressure levels. The area outside the seal ring is equal to the area outside the front cover’s suction port, so the total force on both sides is nearly balanced, leaving only a small residual axial force that is absorbed by the bearing. Under normal conditions, this method effectively balances the axial force. However, it causes more leakage, which can interfere with the impeller's flow and reduce efficiency by 2-5%. It is mainly used in small single-stage centrifugal pumps.

2. **Balancing Pipe**
This approach is similar to using a balancing hole. A mouth ring is placed on the rear impeller cover, aligned with the suction inlet. A balancing pipe connects the sealed space to the pump inlet, helping to equalize the pressure and reduce axial force. The cross-sectional area of the balancing pipe should be at least 4–5 times the area of the mouth ring gap to ensure proper function.

3. **Balancing Vanes**
Radial vanes are placed symmetrically on the back of the impeller. As the impeller rotates, these vanes accelerate the liquid, increasing centrifugal force and reducing the pressure on the back side of the impeller. This helps balance the pressure on both sides of the impeller. However, this method also reduces overall pump efficiency due to increased turbulence and energy loss.

4. **Double-Suction Impeller**
In some single-stage or multi-stage centrifugal pumps, a double-suction impeller is used. This design allows fluid to enter from both sides, naturally balancing the axial thrust. However, achieving perfect symmetry in the flow components is difficult, so a small residual axial force may still exist. This force is typically supported by a single-row radial ball bearing at one end of the shaft.

For multi-stage pumps, additional axial balancing methods are employed, such as symmetrical impeller arrangement, balancing discs, or balance hubs. These mechanisms help counteract the cumulative axial forces generated across multiple stages, ensuring smooth and stable operation of the pump system.

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