What are the causes of vibration in centrifugal pumps?

1. In terms of electrical aspects, imbalances in the magnetic field inside the motor and malfunctions in other electrical systems often cause vibration and noise. For example, in an asynchronous motor during operation, the radial alternating magnetic pulling force between the stator and rotor generated by the interaction of the harmonic fluxes from the stator and rotor teeth, or in a large synchronous motor during operation, situations such as misalignment of the magnetic centers of the stator and rotor or air-gap differences in various directions exceeding the allowable limits, can all cause periodic vibration of the motor and the generation of noise. 2. Mechanically, issues such as uneven mass in the rotating parts of motors and pumps, poor manufacturing quality, inadequate installation, asymmetry in the axis of the unit, vibration levels exceeding acceptable limits, low mechanical strength and stiffness of components, wear and damage to bearings and sealing elements, as well as resonance caused by the pump’s critical speed coinciding with the unit’s natural frequency, can all lead to severe vibration and noise. 3. In terms of hydraulics, uneven flow velocity and pressure distribution at the pump inlet, pressure fluctuations of the working fluid at the pump inlet and outlet, fluid swirling, deviation from the normal flow path, and fluid separation, as well as operating conditions that are not within the specified parameters and pump cavitation caused by various factors, are all common causes of vibration in pump units. Sudden pressure changes in the water conveyance pipelines caused by dynamic transition processes such as pump start-up and shutdown, valve opening and closing, changes in operating conditions, and emergency shutdowns due to accidents often also lead to vibration in the pump house and the machinery.

Analysis of the causes of water pump vibration 1. Causes of water pump vibration There are many factors that can cause vibration in the pumping unit and the building housing the pump; some of these factors are interconnected and interact with each other. Generally speaking, there are mainly the following four categories of causes. 1.1. Electrical aspects: The motor is the main component of the unit; imbalances in the magnetic field within the motor and defects in other electrical systems often cause vibration and noise. For example, in an asynchronous motor during operation, the radial alternating magnetic pulling force between the stator and rotor generated by the interaction of the harmonic fluxes from the stator and rotor teeth, or in a large synchronous motor during operation, situations such as misalignment of the magnetic centers of the stator and rotor or air-gap differences in various directions exceeding the allowable limits, can all cause periodic vibration of the motor and the generation of noise. 1.2. Mechanically, issues such as uneven mass in the rotating parts of motors and pumps, poor manufacturing quality, inadequate installation, asymmetry in the axis of the unit, vibration amplitudes exceeding allowable limits, low mechanical strength and stiffness of components, wear and damage to bearings and sealing elements, as well as resonance caused by the critical speed of the pump coinciding with the natural frequency of the unit, can all lead to severe vibrations and noise. 1.3. In terms of hydraulics, uneven flow velocity and pressure distribution at the pump inlet, pressure fluctuations of the working fluid at the pump inlet and outlet, fluid bypassing, deviation from the normal flow path, and fluid separation, as well as non-normal operating conditions and pump cavitation caused by various factors, are all common causes of vibration in pump units. Dynamic transition processes such as the start-up and shutdown of water pumps, the opening and closing of valves, changes in operating conditions, and emergency shutdowns in case of accidents, which cause sudden pressure changes in the water delivery pipes and water hammer effects, often also lead to vibrations in the pump house and the pumping units. 1.4. Hydraulic and other aspects: An improperly designed water inlet channel for the unit, or one that is not compatible with the unit; an inappropriate submersion depth of the pump; as well as improper sequencing for starting and stopping the unit, can all lead to deteriorated water inlet conditions, the formation of vortices, cavitation, or increased vibration in the unit and the pump house. In units that use destructive siphon vacuum interruption for shutdown, during startup, if it is difficult for air to be entrained in the hump section, the siphon formation time becomes excessively long ； The valve design of the units with door-type flow shut-off is unreasonable; it opens and closes repeatedly, constantly striking the valve seat ； Reasons such as uneven settlement of the foundation that supports the water pump and motor, or poor rigidity of the foundation, can also cause vibration in the unit. 2. Technical measures to eliminate the hazards caused by water pump vibration: In rotating equipment and flowing media, low-intensity mechanical vibration is inevitable. Therefore, during the manufacturing and installation of the unit, it is necessary to avoid interference caused by vibration as much as possible in terms of the unit’s design, operation, and management, in order to minimize the hazards associated with vibration. When vibration occurs in the pump house or the machine unit, it is necessary to analyze the possible causes of such vibration on a case-by-case basis. Once the root cause of the problem is identified, effective technical measures should be taken to eliminate it. Some measures are relatively simple, while others are quite complex. If a large amount of funding is required, a technical and economic comparison of the available options should be conducted, taking into account the technical upgrades of the units. The following outlines the common causes of vibration in motors, water pumps, and pump houses, as well as the measures to eliminate it. 2.1. Common causes of motor vibration and countermeasures: Uneven bearing wear: Misalignment of the unit or worn bearings. Remedial measures: Realign the concentricity of the unit, and adjust or replace the bearings. Stator-rotor friction: uneven air gap or bearing wear. Remedial measures: Readjust the air gap, adjust or replace the bearings; the rotor must not be able to stop at any position, nor should there be a power imbalance. Remedial action: Rebalance the rotor statically and dynamically. Axial looseness: The screw is loose or improperly installed. Remedial action: Tighten the screws and check the installation quality. The foundation is vibrating: poor foundation stiffness or loose corner screws. Remedial measures: Reinforce the foundation or tighten the bottom corner screws. Unstable three-phase current: reduced torque, fault in the rotor bars or end rings. Remedial action: Inspect and repair the rotor bar slots or end rings. 2.2. Common causes of pump vibration and measures to eliminate them: Difficulty in manually turning the pump shaft: bent pump shaft, worn bearings, misalignment of the unit, and the impeller hitting the pump casing. Remedial measures: Straighten the pump shaft, adjust or replace the bearings, realign the concentricity of the unit, and readjust the clearance. Excessive pump shaft wobble: Wear of bearings and journal surfaces or excessive clearance. Remedial measures: Repair the shaft journal, adjust or replace the bearings. Hydraulic imbalance: Imbalance of the impeller, or blockage or damage in certain vanes of the centrifugal pump. Remedial measures: Re-check the static and dynamic balance of the impeller, remove blockages, and repair or replace the impeller. Excessive shaft power in axial flow pumps: the water level in the inlet tank is too low, the immersion depth of the impeller is insufficient, debris gets entangled around the impeller, the degree of cavitation damage to the pump varies, and the impeller is damaged. Remedial measures: Raise the water level in the inlet tank, lower the installation height of the pump to remove debris, install trash racks, and repair or replace the impeller. Foundation vibration: poor foundation stiffness, loose corner screws, or resonance. Remedial measures: Reinforce the foundation, tighten the foot screws. The efficiency of the centrifugal pump unit drops sharply, or the efficiency of the axial flow pump unit decreases slightly, accompanied by cavitation noise. Remedial measures: Change the pump speed to avoid the resonance range, identify the cause of cavitation, and take actions to eliminate it. 2.3. Unit vibration caused by other reasons and mitigation measures: Blockage of the trash rack, decrease in the water level of the inlet tank. Remedial measures: Clean the trash racks, and install devices for cleaning the trash racks. The design of the front pool and the water intake pool is unreasonable, and the mismatch between the water intake channel and the pump worsens the water intake conditions. Remedial measures: Clean the trash racks, install appropriate trash rack cleaning devices, and optimize the design of the inlet forebay, intake basin, and inlet water channels. The time required to form a siphon is too long, causing the unit to operate under conditions other than those designed for an extended period. Remedial measures: Install a vacuum pumping device, and design and improve the siphonic water discharge channel appropriately. The water inlet pipe is not securely fixed, causing resonance. Remedial measures: Add pipeline pier caps and supports, reinforce pipeline supports, and adjust operating parameters to avoid the resonance zone. Repetitive knocking on the door, or excessive force when closing it. Remedial measures: Install exhaust vents before the outlet of the flow channel (or pipeline), and design the check valves properly to take control measures and reduce the impact force when the check valves close. Sudden pressure changes in the outlet pipe and water hammer effect. Remedial measures: check valves and pressure regulating chambers, among other water hammer prevention measures. The improper sequence of unit startup and shutdown led to deteriorated water intake conditions for the pump. Remedial measure: Optimize startup and shutdown sequence

Loose foundation bolts, cavitation, and loose couplings are among the more common issues, right?:)

It has been clearly answered upstairs; additionally, a low liquid level inside the tower can also cause vibration in the centrifugal pump

Reason | Solution
Loose pump foot bolts or shims | Tighten the bolts and spot-weld the shims
Incorrect centering of the pump | Switch to a backup pump and contact maintenance
Excessive bearing clearance | Switch to a backup pump and contact maintenance
Bent pump shaft | Switch to a backup pump and contact maintenance
Imbalanced rotor, damaged impeller, blocked flow channels, blocked balance pipes, etc. | Switch to a backup pump and contact maintenance
Loose internal components of the pump | Switch to a backup pump and contact maintenance
Pump under vacuum | Apply pressure to resolve the issue
Broken bearing rollers | Switch to a backup pump and contact maintenance
Cavitation | Identify the cause of cavitation and take corrective action
Incorrect alignment of the coupling | Have a blacksmith realign it
Loose foundation | Rebuild the foundation
Changes in process flow rate | Stabilize the flow rate and observe further
That’s all I can think of for now.

First, look at sudden changes in process conditions, such as sudden increases or decreases in flow rate. Then examine problems with the pump itself, as well as issues related to installation, electrical aspects, and mechanical components

1. The center is not aligned. 2. The coupling bolts are loose, or the soft connections such as washer plates are damaged. 3. The foundation bolts of the motor or pump are loose. 4. There are problems inside the pump, such as a loose impeller or imbalance.

The alignment of the 1 coupling is poor. 2 Pump is evacuated or suffering from cavitation. 3 The diaphragm or plum blossom pad is damaged. 4 The pump shaft is bent or the impeller is unbalanced. 5 The bearing radial clearance is too large. 6 Move the feet.