Slurry pump impeller balance hole

Some impellers of slurry pumps have balancing holes.
The balance hole, also called the return port, is mainly used to balance the axial force generated by the impeller during operation and reduce the wear of the bearing end face and the wear of the thrust plate.
When the impeller rotates, the liquid in the impeller is thrown from the center of the impeller along the flow path between the blades to the surroundings of the impeller under the action of centrifugal force. Because the liquid is affected by the blades, the pressure and speed increase at the same time, creating a forward direction. The purpose of drilling holes in the impeller is to reduce the axial force generated by the impeller to protect the bearings, thrust plate and control pump pressure.
The degree of axial force reduction depends on the number and diameter of the pump holes. The sealing ring and the balancing hole complement each other. The disadvantage of using this balancing method is that there will be a loss of efficiency.
Generally, the leakage amount of the balance hole is about 2%-5% of the design flow rate.
In addition, the leakage flow through the balance hole collides with the main liquid flow entering the impeller, destroying the normal flow state and reducing 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.
The leakage through the balance hole increases. Although the head increases, the pressure in the lower chamber of the sealing ring is still very low, so the axial force further decreases.
When the flow rate is large, the axial force also becomes smaller due to the decrease in head.