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

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    What are the mechanical losses and mechanical efficiency of a multistage pump?

    Publication Date:

    2026-02-02

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    During the operation of a multistage pump, not all of the energy supplied by the motor is converted into effective power for liquid delivery—some of the energy is lost due to friction in mechanical components and operational resistance; this is known as mechanical loss. The ratio of effectively utilized energy to the input energy is called mechanical efficiency. These two indicators directly determine the pump’s energy consumption level, operational stability, and service life, making them crucial references for pump selection and maintenance. In this article, the manufacturer of multistage pumps... Changsha Zhonglian Pump Industry The technician will now explain what mechanical losses and mechanical efficiency are in multistage pumps.
     
    Multistage pump
     
     
    The core components of mechanical losses fall into three categories, all arising from actual wear and tear during component operation:
    1. Bearing friction losses: As the pump shaft rotates, the contact friction between the rolling elements inside the bearing and the inner and outer races as well as the retainer consumes energy. Lubrication conditions and bearing type (rolling bearings or sliding bearings) directly affect the magnitude of these losses. High-quality lubricants can reduce friction losses by more than 30%.
    1. Sealing device losses: The relative rotation between the shaft seal and the pump shaft generates frictional resistance. Friction losses in packing seals are typically higher than those in mechanical seals, which is one of the reasons why mechanical seals have become the mainstream configuration for high-efficiency multistage pumps.
    1. Disc friction loss: As the impeller rotates, the liquid between its front and rear shrouds and the inner wall of the pump cavity experiences friction. At the same time, this friction drives the surrounding liquid to rotate, creating vortices. This energy loss is particularly significant in high-speed multistage pumps, accounting for 40% to 60% of the total mechanical losses.
     
    Mechanical efficiency is a key indicator for measuring energy utilization efficiency. Its calculation formula is: Mechanical efficiency (ηm) = Input hydraulic power / Shaft power × 100%.
    Among these, shaft power refers to the total power transmitted by the motor to the pump shaft, while input hydraulic power is the effective power actually used to drive fluid flow. The mechanical efficiency of industrial-grade multistage pumps typically ranges from 85% to 95%; high-quality products can achieve efficiencies exceeding 92%, whereas inefficient pumps may have efficiencies below 80%. Prolonged operation of such inefficient pumps can lead to significant energy waste.
    Key factors affecting mechanical efficiency include: component machining accuracy (misalignment errors in the impeller and bearing housing can exacerbate losses); lubrication conditions (regular replacement of appropriate grease can maintain efficient operation); and operating conditions (deviation from rated flow and head can lead to increased mechanical losses). For example, rolling bearings have mechanical losses that are 30% to 50% lower than those of sliding bearings, and disc friction losses in high-precision impellers can be reduced by about 15%.
    For practical applications, reducing mechanical losses and improving mechanical efficiency can directly lower electricity costs and extend the service life of components. When selecting equipment, pay close attention to the mechanical efficiency parameter; during operation, ensure proper lubrication of bearings and maintenance of seals, and avoid prolonged operation under excessive load—all of these are crucial measures for ensuring the efficient operation of multistage pumps.
     

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