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10 Major Causes Of Centrifugal Pump Vibration

1. Shaft

Pumps with long shafts are prone to insufficient shaft stiffness, excessive deflection, and poor straightness of the shaft system, causing friction between the moving parts (drive shaft) and static parts (sliding bearings or mouth rings), resulting in vibration. In addition, the pump shaft is too long and is greatly affected by the impact of flowing water in the pool, which increases the vibration of the underwater part of the pump. If the balance plate gap at the shaft end is too large, or the axial working movement is improperly adjusted, it will cause the shaft to move at a low frequency and cause the bearing bush to vibrate. The eccentricity of the rotating shaft will cause a bending vibration of the shaft.

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2. Foundation and pump frame

The contact fixation form between the drive device frame and the foundation is not good, and the foundation and motor system have poor vibration absorption, transmission, and isolation capabilities, resulting in excessive vibrations of both the foundation and the motor. If the water pump foundation is loose, or the water pump unit forms an elastic foundation during the installation process, or the foundation stiffness is weakened due to oil-immersed water bubbles, the water pump will generate another critical speed with a phase difference of 1800 from the vibration, thereby increasing the vibration frequency of the water pump. If the increase If the frequency is close to or equal to the frequency of an external factor, the amplitude of the water pump will increase. In addition, loose foundation anchor bolts will reduce the restraint stiffness and intensify the vibration of the motor.

3. Coupling

The circumferential spacing of the connecting bolts of the coupling is poor, and the symmetry is destroyed; the extension section of the coupling is eccentric, which will generate eccentric force; the taper of the coupling is out of tolerance; the static balance or dynamic balance of the coupling is not good; The fit between the elastic pin and the coupling is too tight, causing the elastic pin to lose its elastic adjustment function and causing the coupling to not be well aligned; the matching gap between the coupling and the shaft is too large; The mechanical wear of the coupling rubber ring causes the coupling performance of the coupling rubber ring to decrease; the quality of the transmission bolts used on the coupling is not equal to each other. These reasons all cause vibration.

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4. Factors of the water pump itself

Asymmetric pressure field generated when the impeller rotates; vortices in the suction pool and inlet pipe; occurrence and disappearance of vortices inside the impeller, volute, and guide vanes; vibrations caused by vortices caused by half-open valves; due to the limited number of impeller blades Uneven outlet pressure distribution; deflow in the impeller; surge; pulsating pressure in the flow channel; cavitation; water flows in the pump body, which will cause friction and impact on the pump body, such as water hitting the baffle tongue and the front of the guide vane. The edge of the pump body causes vibration; boiler feed water pumps that transport high-temperature water are prone to cavitation vibration; the pressure pulsation in the pump body is mainly due to the pump impeller sealing ring. The gap in the pump body sealing ring is too large, resulting in large leakage losses and serious backflow in the pump body, this in turn causes an imbalance of the rotor axial force and pressure pulsation, which will enhance vibration.

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5. The motor

The motor structural parts are loose, the bearing positioning device is loose, the iron core silicon steel sheet is too loose, and the support stiffness of the bearing is reduced due to wear, which will cause vibration. Mass eccentricity, uneven rotor mass distribution caused by rotor bending, or mass distribution problems cause static and dynamic balance quantities to exceed standards.

In addition, the squirrel cage bars of the rotor of the squirrel-cage motor is broken, causing an imbalance between the magnetic field force on the rotor and the rotational inertia force of the rotor, causing vibration. The motor phase loss, unbalanced power supply of each phase, and other reasons can also cause vibration. In the motor stator winding, due to quality problems during the installation process, the resistance between the phase windings is unbalanced, resulting in an uneven magnetic field and an unbalanced electromagnetic force. This electromagnetic force becomes the excitation force and causes vibration.

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6. Water pump selection and variable operating conditions operation

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Each pump has its own rated operating point. Whether the actual operating conditions are consistent with the designed operating conditions has an important impact on the dynamic stability of the pump. The water pump operates relatively stably under the design working conditions, however, when operating under variable working conditions, the vibration increases due to the radial force generated in the impeller; a single pump is improperly selected, or two mismatched pump models are connected in parallel. These will cause vibration in the pump.

7. Bearings and lubrication

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If the stiffness of the bearing is too low, it will cause the first critical speed to decrease and cause vibration. In addition, poor performance of the guide bearing leads to poor wear resistance, poor fixation, and excessive bearing clearance, which can easily cause vibration; while the wear of the thrust bearing and other rolling bearings will intensify the longitudinal scurrying vibration and bending vibration of the shaft at the same time. Improper selection of lubricating oil, deterioration, excessive impurity content, and lubrication failure caused by poor lubrication pipelines will cause the bearing working conditions to deteriorate and cause vibration. The self-excitation of the oil film of the motor sliding bearing will also produce vibration.

8. Pipes and their installation and fixation

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The outlet pipe support of the pump is not rigid enough and deforms too much, causing the pipe to press down on the pump body, destroying the neutrality of the pump body and the motor; the pipe is too strong during the installation process, and the inlet and outlet pipes are internally damaged when connected to the pump. The stress is large; the inlet and outlet pipelines are loose, and the restraint stiffness is reduced or even fails; the outlet flow channel is completely broken, and the debris is stuck in the impeller; the pipeline is not smooth, such as an airbag at the water outlet; the water outlet valve is off the plate, or is not opened; the water inlet is damaged Intake air, uneven flow field, and pressure fluctuations. These reasons will directly or indirectly cause vibration of the pump and pipeline.

9. Cooperation between parts

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The concentricity of the motor shaft and the pump shaft is out of tolerance; a coupling is used at the connection between the motor and the transmission shaft, and the concentricity of the coupling is out of tolerance; the design between dynamic and static parts (such as between the impeller hub and the mouth ring) The wear of the gap becomes larger; the gap between the middle bearing bracket and the pump cylinder exceeds the standard; the gap between the sealing ring is inappropriate, causing imbalance; the gap around the sealing ring is uneven, such as the mouth ring is not grooved or the partition is not grooved, it will This happens. These adverse factors can cause vibration.

10. Impeller

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Centrifugal pump impeller mass eccentricity. The quality control during the impeller manufacturing process is not good, for example, the casting quality and machining accuracy are unqualified; or the transported liquid is corrosive, and the impeller flow channel is eroded and corroded, causing the impeller to become eccentric. Whether the number of blades, outlet angle, wrap angle, and the radial distance between the throat partition tongue and the impeller outlet edge of the centrifugal pump impeller are appropriate, etc. During use, the initial friction between the impeller orifice ring and the pump body orifice ring of the centrifugal pump, and between the interstage bushing and the partition bushing, gradually turns into mechanical friction and wear, which will aggravate the vibration of the centrifugal pump.

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