Whether the pump vibrates abnormally is an important indicator to evaluate whether the quality of the pump is reliable. There are many reasons for the vibration of the multi-stage pump, such as the influence of water flow conditions, the complexity of fluid motion, dynamic and static balance, and high-speed rotating parts, which may affect the stability of the pump. The following is a comprehensive analysis of the reasons for the vibration of the water pump.      

10 Causes of Vibration:  

1. Axis

   The pump shaft is very long, and it is easy to cause friction between the moving part (transmission shaft) and the static part (sliding bearing or mouth ring) due to insufficient stiffness of the pump, too large deflection, poor straightness of the shaft system, etc., resulting in the vibration of the pump If the pump shaft is too long, it will be greatly affected by the impact of the flowing water in the pool, which will increase the vibration of the underwater part of the multi-stage pump, the clearance of the balance disc of the pump shaft is too large, or the improper adjustment of the axial working momentum will also cause the low frequency of the shaft. Playing, causing the bearing pad to vibrate, the eccentricity of the rotating shaft will also cause the bending vibration of the shaft.

2. Foundation and pump bracket

   The contact fixing form between the drive frame and the foundation is not good, and the foundation and the motor system have poor ability to absorb, transmit and isolate vibration, resulting in excessive vibration of the foundation and the motor, the foundation of the pump is loose, or the pump unit forms elasticity during the installation process The foundation, or the foundation stiffness is weakened due to the oil-immersed water bubble, the water pump will generate another critical speed with a phase difference of 1800 from the vibration phase, so that the vibration frequency of the water pump will increase. If the increased frequency is close to or equal to the frequency of an external factor, the It will increase the amplitude of the multistage pump. In addition, the loosening of the foundation anchor bolts reduces the restraint rigidity and aggravates the vibration of the motor.

3. Coupling

   The circumferential spacing of the coupling bolts is poor, the symmetry is destroyed, the coupling extension section is eccentric, and eccentric force will be generated, the coupling taper is out of tolerance, the static balance or dynamic balance of the coupling is not good, and the elasticity The fit between the pin and the coupling is too tight, so that the elastic pin loses its elastic adjustment function, and the coupling cannot be well aligned, the clearance between the coupling and the shaft is too large, and the mechanical wear of the coupling rubber ring The fitting performance of the coupling rubber ring is reduced, and the quality of the transmission bolts used on the coupling varies from each other. These reasons will cause the multistage pump to vibrate.

4. Factors of the pump itself

   The asymmetric pressure field generated when the impeller rotates; the vortex in the suction pool and the water inlet pipe; the occurrence and disappearance of the vortex inside the impeller, the volute, and the guide vane; the vibration caused by the vortex caused by the half-opening of the valve; due to the limited number of impeller blades Uneven distribution of outlet pressure; de-flow in the impeller; surge; pulsating pressure in the flow channel; cavitation; water flowing in the pump body will have friction and impact on the pump body, such as the water flow hitting the front of the separating tongue and guide vane Boiler feed pumps that transport high temperature water are prone to cavitation vibration; the pressure pulsation in the pump body is mainly caused by the seal ring of the pump impeller. Causes unbalanced rotor axial force and pressure pulsation, which will enhance vibration.

   In addition, for the stainless steel hot water pump that transports hot water, if the preheating of the pump is uneven before starting, or the sliding pin shaft system of the pump does not work properly, the thermal expansion of the pump group will cause severe vibration during the starting stage; the pump body comes from thermal expansion. If the internal stress cannot be released, it will cause the change of the stiffness of the shaft support system. When the changed stiffness is in an integral multiple of the angular frequency of the system, resonance occurs.

 5. Motor

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

   In addition, the squirrel cage bar of the squirrel-cage motor rotor is broken, which causes the magnetic field force on the rotor and the rotational inertia force of the rotor to be unbalanced and causes vibration. In the stator winding of the motor, due to the operation quality of the installation process, the resistance between the windings of each phase is unbalanced, resulting in an uneven magnetic field and an unbalanced electromagnetic force. This electromagnetic force becomes the excitation force and causes vibration.

6. Pump selection and variable working conditions

   Each pump has its own rated operating point. Whether the actual operating conditions conform to the design conditions has an important impact on the dynamic stability of the pump. The pump runs relatively stably under the design conditions, but when it runs under variable conditions, the vibration is increased due to the radial force generated in the impeller, the single pump is improperly selected, or the two types of pumps do not match. in parallel. These will cause the multistage pump to vibrate.

7. Bearings and lubrication

   If the stiffness of the bearing is too low, the first critical speed will be reduced, causing vibration. In addition, the poor performance of the guide bearing leads to poor wear resistance, poor fixation, and excessive bearing clearance, which is also prone to vibration, while the wear of the thrust bearing and other rolling bearings will increase the longitudinal 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 pipeline will cause deterioration of bearing conditions and cause vibration. Self-excitation of the motor sliding bearing oil film will also cause vibration.

8. Pipes and their installation and fixation

   The rigidity of the outlet pipe bracket of the pump is not enough, and the deformation is too large, which causes the pipe to be pressed down on the pump body, which causes the neutrality of the pump body and the motor to be damaged. The stress is large, the inlet and outlet pipelines are loose, the restraint rigidity is reduced or even fails, the outlet flow channel is partially broken, the debris is stuck in the impeller, and the pipeline is not smooth, such as the air bag at the water outlet, the water outlet valve is dropped, or not opened, and the water inlet has Intake, uneven flow field, and pressure fluctuations will directly or indirectly lead to the vibration of multi-stage pumps and pipelines.

9. Coordination between components

   The concentricity of the motor shaft and the pump shaft is out of tolerance, the coupling between the motor and the transmission shaft is used, the concentricity of the coupling is out of tolerance, the design between the dynamic and static parts (such as between the impeller and the mouth ring) The wear of the clearance becomes larger, the clearance between the intermediate bearing bracket and the pump cylinder exceeds the standard, the clearance of the sealing ring is not suitable, resulting in an imbalance, and the clearance around the sealing ring is not uniform, such as the groove of the mouth ring or the groove of the partition plate, which will cause imbalance. This happens. These unfavorable factors can cause the multistage pump to vibrate.

10. Impeller

   The quality of the pump impeller is eccentric, and the quality control of the impeller 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, resulting in the eccentricity of the impeller. Whether the number of blades of the pump impeller, the outlet angle, the wrap angle, the radial distance between the throat separation tongue and the outlet edge of the impeller is appropriate, etc. In use, between the impeller port ring and the pump body port ring of the multistage pump, between the interstage bushing and the diaphragm bushing, the initial friction gradually becomes mechanical friction and wear, which will aggravate the multistage pump. vibration.