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About the Balance Hole of the Split Case Pump Impeller

June 12,2023

The balance hole (return port) is mainly to balance the axial force generated when the impeller is working, and reduce the wear of the bearing end surface and the wear of the thrust plate. When the impeller rotates, the liquid filled in the impeller will flow from the impeller to The center is thrown to the periphery of the impeller along the flow channel between the blades.

As the liquid is affected by the blades, the pressure and velocity increase at the same time, generating a forward axial force.

The hole in the impeller ofsplit case pumpis to reduce the axial force generated by the impeller. Force. Plays a role in protecting bearings, thrust discs and controlling pump pressure.


The degree of reducing the axial force depends on the number of pump holes and the size of the hole diameter. It is worth noting that the sealing ring and the balance hole are complementary. The disadvantage of using this balance method is that there will be a loss of efficiency (the leakage of the balance hole is generally 2% to 5% of the design flow).

In addition, the leakage flow through the balance hole collides with the main liquid flow entering the impeller, which destroys the normal flow state and reduces the anti-cavitation performance.

At non-rated flow, the flow state changes. When the flow rate is small, due to the influence of pre-rotation, the pressure at the center of the impeller inlet is lower than the pressure at the outer periphery, and the leakage through the balance hole increases. Although the split case pump head increases, the pressure in the lower chamber of the sealing ring is still very low, so the axial force is further reduced. Small. When the flow rate is large, the axial force becomes smaller due to the drop of the head.

Some research results show that: the total area of the balance hole is 5-8 times the gap area of the mouth ring, and better performance can be obtained.

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