Changsha Zoomlian Pump Co., Ltd. 长沙中联泵业股份有限公司

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    Analysis of the Structural Positioning of the Balance Pipe and Axial Force Balancing Technology in Horizontal Multistage Centrifugal Pumps

    Publication Date:

    2026-03-22

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    Over many years of development, horizontal multistage centrifugal pumps have adopted a variety of methods for balancing axial forces; the effectiveness of the axial-force-balancing system directly affects operational stability. In horizontal multistage centrifugal pumps employing balance discs and drum-type structures, the balance pipe—acting as a critical component in single-stage centrifugal pumps—achieves axial-force cancellation through pressure guidance. In the following discussion, Centrifugal pump Manufacturer Changsha Zoomlion Pump Industry The technical engineer will provide a technical analysis of the structural positioning of the balance pipe in horizontal multistage centrifugal pumps and the associated axial-force-balancing technology.

     

    Horizontal multistage centrifugal pump

     

    I. Structural Positioning of the Balance Pipe

    In the design of Zoomlion Pumps in Changsha, the balance pipe is typically installed on the outer side of the impeller shroud, near the hub at the high-pressure end. The specific connection route is as follows: high-pressure fluid is drawn from the outlet seal ring on the impeller back cover (the high-pressure side) and routed via an external connecting pipe to the low-pressure inlet of the pump. This design establishes a dynamic pressure equilibrium between the two sides of the impeller, effectively reducing rotor axial runout.

     

    II. Principle of Axial Force Balance

    When the impeller is operating, a portion of the high-pressure fluid at the outlet penetrates to the back side of the impeller disc, creating a high-pressure zone that generates a pressure differential relative to the low-pressure zone at the inlet. The balance pipe reduces this pressure differential from ΔP to ΔP' by diverting high-pressure fluid from the high-pressure side to the low-pressure side, thereby counteracting the axial thrust. It should be noted that the balance pipe can only partially offset the axial force; approximately 10–15% of the remaining axial force must be borne by the bearing system.

     

    III. Technical Characteristics of the Balance Tube

    1. Advantages: simple structure, low cost, and suitable for single-stage centrifugal pumps with stable flow;

    2. Limitations: Internal leakage losses result in a reduction of pump efficiency by approximately 2–3% and the pump is sensitive to fluctuations in inlet pressure.

     

    IV. Comparison of Other Axial Force Balancing Solutions

    Balancing method Applicable Scenarios Technical Features
    Balance hole Single-stage single-suction centrifugal pump Symmetrical drilling is used to reduce the pressure differential on both sides, and must be employed in conjunction with a sealing ring. This approach is suitable for applications requiring high precision; care must be taken to ensure consistent blade profile geometry.
    Double-suction impeller High-flow conveyance It features a double-suction design, which theoretically eliminates axial thrust and is suitable for high-flow applications.
    Balance disc Multistage centrifugal pump The cancellation of the pressure gradient is achieved through a labyrinth structure and requires adjustment in conjunction with a guide vane ring. This design is suitable for multistage centrifugal pumps and delivers excellent balancing performance.
    Balance drum High differential pressure conditions It leverages the resistance generated by the clearance between the drum body and the pump casing for balance, making it suitable for applications with complex shaft-seal systems and particularly effective under high-pressure-difference operating conditions.

     

    V. Recommendations from Changsha Zoomlion Pump Industry:

    When the system flow rate is less than 500 m³/h, a combination of a balance pipe and thrust bearings should be prioritized; when the flow rate exceeds 500 m³/h and the pressure exceeds 1.6 MPa, it is recommended to upgrade to a balance disc or balance drum system. The installation of the balance pipe must ensure that the connection pipe diameter is appropriately matched (typically DN20–DN50), and that 316L stainless steel is used for the pipe material to resist media corrosion.

     

    VI. Operational and Maintenance Precautions

    1. Blockage of the balance pipe can cause the impeller to seize; it is recommended to perform endoscopic inspection every 3,000 operating hours.

    2. Prior to startup, ensure that the balance line is free of blockages and that the inlet pressure is stable within ±5% of the design value.

     

    Changsha Zoomlion Pump Industry consistently designs axial-force counterbalance solutions based on the “system-level balance” concept. The balance pipe, as a fundamental technical solution, is often combined with other balancing systems to ensure stable equipment operation across the entire range of operating conditions.

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