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

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    Causes of Unstable Rotational Speed in Multistage Centrifugal Pumps and Corresponding Solutions

    Publication Date:

    2026-03-27

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    Multistage centrifugal pumps serve as core equipment for fluid conveyance in industrial, agricultural, and municipal applications, and their speed stability directly affects system operational efficiency and product quality. When speed fluctuations occur in multistage centrifugal pumps, a systematic diagnosis must be conducted across electrical, mechanical, fluid, control, and environmental dimensions. In this paper, Centrifugal pump Manufacturer Changsha Zoomlion Pump Industry Based on technical practice, this paper analyzes the causes of unstable rotational speed in typical multistage centrifugal pumps and proposes corresponding solutions for reference by user organizations.

     

    Multistage centrifugal pump

     

     

    I. Electrical System Abnormalities

    1. Power supply fluctuations: Unstable voltage or current distortion can cause uncontrolled motor speed. It is necessary to use professional power monitoring equipment to assess power quality and, if required, install voltage stabilizers or filtering modules.

    2. Controlling Parameter Deviations: Improper setting of inverter parameters—such as incorrect carrier frequency or misconfigured acceleration/deceleration times—can lead to speed oscillations. Changsha Zoomlion Pump Industry recommends using the manufacturer’s dedicated parameter calibration tool to ensure that the PID control loop gains are properly matched to the pump’s characteristics.

     

    II. Mechanical Transmission Failures

    1. Bearing wear: Excessive radial clearance or lubrication failure in rolling bearings can lead to periodic speed fluctuations. Regular inspection of bearing radial clearance is required (recommended ≤0.1 mm), and high-precision bearings from brands such as SKF should be used, with lubrication performed in accordance with ISO 18436.

    2. Shaft Alignment Deviation: When the coaxiality error between the pump shaft and the motor shaft exceeds 0.05 mm/m, additional bending moments will be generated. Changsha Zoomlion Pump Industry uses laser alignment instruments (such as the SKF laser alignment system) for dynamic alignment, ensuring that the coupling concentricity is no greater than 0.03 mm.

     

    III. Fluid Condition Interference

    1. Flow Fluctuations: Sudden changes in pipeline flow—such as those caused by inadvertent valve operation—can induce shifts in the pump performance curve. It is recommended to optimize the piping design by installing a surge tank at the pump inlet or by employing a variable-frequency drive system to achieve constant-flow control.

    2. Changes in fluid properties: Abnormal fluid viscosity—such as crystallization of the medium or excessive gas content—can result in a mismatch between pump head and rotational speed. Changsha Zoomlion Pump Industry recommends monitoring viscosity using an online viscometer and, when necessary, installing a dual-pump switching system to handle extreme operating conditions.

     

    IV. Control System Fault  

    1. Sensor failure: Interruption of the signal from the speed sensor (such as a Hall-effect sensor or a magneto-electric speed probe) will cause the closed-loop control to fail. The sensor accuracy must be verified regularly (with an error ≤ ±0.5% FS), and probes with an IP68 protection rating should be used to prevent interference from dust.

    2. Actuator jamming: Aging of the inverter’s power module or erosion of contactor contacts can lead to unstable output voltage. It is recommended to implement a customized redundant control solution developed by Changsha Zhonglian Pump Industry, with a redundancy level of ≥99.9% for critical components.

     

    V. Environmental and Operations & Maintenance Factors  

    1. Vibration interference: Foundation vibrations (e.g., loosening of motor anchor bolts exceeding 0.02 mm) can induce resonance. It is necessary to use damping vibration isolators independently developed by Changsha Zoomlion Pump Industry to limit the vibration transmissibility to ≤15%.

    2. Lack of Maintenance: Failure to perform preventive maintenance in accordance with the ISO 50001 standard—such as failing to regularly replace mechanical seals or clean impeller passages—can lead to fouling and jamming. It is recommended to establish a three-tier maintenance system, with replacement intervals for critical components not exceeding 80% of their design service life.

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