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Ten major causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps

11 May 2021Email

  Vibration is an important index to evaluate the operational reliability of chemical corrosion-resistant centrifugal pump units. The main hazards of excessive vibration are: vibration causes the pump unit to fail to operate normally; it causes vibration of the motor and pipeline, causing damage to the machine; causing damage to the bearing and other parts; causing loose connection parts, basic cracks or motor damage; The pipes or valves connected to the water pump are loose or damaged; vibration and noise are formed.

   There are many reasons for the vibration of chemical corrosion-resistant centrifugal pumps. The shaft of the pump is generally directly connected with the shaft of the drive motor, so that the dynamic performance of the pump and the dynamic performance of the motor interfere with each other; there are many high-speed rotating parts, and the dynamic and static balance can meet the requirements; the parts that interact with the fluid are greatly affected by the water flow; The complexity of fluid movement itself is also a factor that limits the stability of pump dynamic performance.

 

  Top ten causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-shaft

  Pumps with very long shafts are prone to insufficient shaft rigidity, too much deflection, and poor shaft straightness, causing friction between the moving part (transmission shaft) and the static part (sliding bearing or mouth ring), resulting in vibration. In addition, the pump shaft is too long and is greatly affected by the impact of the flowing water in the pool, which increases the vibration of the underwater part of the pump. Excessive clearance of the balance disc at the shaft end or improper adjustment of the axial working displacement will cause the shaft to move at low frequency and cause the bearing bush to vibrate. The eccentricity of the rotating shaft will cause bending vibration of the shaft.


   Ten major causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-foundation and pump bracket

  The contact and fixing form used between the drive device frame and the foundation is not good, and the foundation and the motor system have poor ability to absorb, transmit, and isolate vibration, which causes the vibration of the foundation and the motor to exceed the standard. The foundation of the water pump is loose, or the water pump unit forms an elastic foundation during the installation process, or the foundation stiffness is weakened due to oil-soaked water bubbles, the water pump will generate another critical speed with a phase difference of 1800 from the vibration, which will increase the vibration frequency of the water pump. The frequency is close to or equal to the frequency of a certain external factor, which will increase the amplitude of the pump. In addition, the loosening of the foundation anchor bolts results in a decrease in the restraint rigidity and aggravates the vibration of the motor.

 

  Top ten causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-couplings

The circumferential spacing of the coupling bolts is poor, and the symmetry is destroyed; the coupling extension section is eccentric, which will produce eccentric force; the coupling taper is out of tolerance; the coupling static or dynamic balance is not good; elasticity The fit between the pin and the coupling is too tight, so that the elastic pin loses the elastic adjustment function and the coupling cannot be well aligned; the coupling gap between the coupling and the shaft is too large; the mechanical wear of the coupling rubber ring Coupling performance of the coupling rubber ring is reduced; the quality of the transmission bolts used on the coupling is different from each other. These reasons will cause vibration
move.

 

   Ten major causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-factors of the pump itself

The asymmetric pressure field generated when the impeller rotates; the vortex of the suction pool and the inlet pipe; the occurrence and disappearance of the vortex inside the impeller and 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; outflow 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 water flow hitting the front of the diaphragm and guide vane Boiler feed water pumps that deliver high temperature water are prone to cavitation vibration; pressure pulsation in the pump body is mainly caused by the seal ring of the pump impeller. The gap of the seal ring of the pump body is too large, resulting in large leakage losses in the pump body and serious backflow. The imbalance of the rotor axial force and pressure pulsation will increase the vibration. In addition, for conveying
For hot water hot water pumps, if the preheating of the pump is uneven before starting, or the sliding pin system of the pump is not working properly, thermal expansion of the pump set will be induced, which will induce violent vibration in the starting stage; the internal stress of the pump body comes from thermal expansion and other aspects. Failure to release will cause changes in the rigidity of the shaft support system. When the changed rigidity becomes an integral multiple of the angular frequency of the system, resonance occurs.

 

   Ten major causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-motors

  The motor structure is loose, the bearing positioning device is loose, the iron core silicon steel sheet is too loose, the bearing is worn and the support rigidity decreases, 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 rotor of the squirrel cage motor is broken, causing the magnetic field force of the rotor and the rotating inertia force of the rotor to be unbalanced and causing vibration. The lack of phase of the motor and the unbalance of the power supply of each phase can also cause vibration. In the stator winding of the motor, due to the operation quality problem of the installation process, the resistance between the phase windings is unbalanced, which causes the generated magnetic field to be uneven, and unbalanced electromagnetic force is generated. This electromagnetic force becomes an exciting force and causes vibration.

 

   Ten causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-pump selection and variable working conditions operation

  Each pump has its own rated operating conditions. Whether the actual operating conditions are consistent with the design conditions has an important impact on the dynamic stability of the pump. The pump runs relatively stable under design conditions, but when operating 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 pump to vibrate.

 

   Ten causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-bearings and lubrication

  The rigidity of the bearing is too low, which 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, excessive bearing gaps, and vibrations. The wear of thrust bearings and other rolling bearings will aggravate the longitudinal movement vibration and bending vibration of the shaft. . Lubrication failure caused by improper selection of lubricants, deterioration, excessive impurity content and poor lubrication pipelines will cause deterioration of bearing conditions and cause vibration. The self-excitation of the oil film of the motor sliding bearing also produces vibration.

 

   Ten major causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-pipes and their installation and fixation

The pump outlet pipe support is not rigid enough, and the deformation is too large, causing the pipe to press down on the pump body, causing the pump body and the motor to be neutralized; the pipe is too strong during the installation process, and the inlet and outlet pipes are connected to the pump. High stress; Inlet and outlet pipelines are loose, restraining rigidity decreases or even fails; all parts of the outlet flow channel are broken, and fragments are stuck in the impeller; the pipeline is not smooth, such as an air bag at the outlet; the outlet valve is off or not open; the inlet has Intake, uneven flow field, pressure fluctuation. These reasons will directly or indirectly cause the vibration of the pump and pipeline.

 

   Ten causes of vibration/vibration of chemical corrosion-resistant centrifugal pumps-coordination between parts

The concentricity of the motor shaft and the pump shaft is out of tolerance; the coupling between the motor and the drive shaft is used, and the concentricity of the coupling is out of tolerance; the design between moving and static parts (such as between the impeller and the mouth ring) The abrasion of the gap becomes larger; the gap between the intermediate bearing bracket and the pump barrel exceeds the standard; the gap of the sealing ring is not suitable, resulting in an imbalance; the gap around the sealing ring is uneven, such as the mouth ring groove or the partition groove. This happened. These unfavorable factors can cause vibration.

 

   Ten reasons for vibration/vibration of chemical corrosion-resistant centrifugal pumps-impeller

   The mass of centrifugal pump impeller is eccentric. The quality control in the impeller manufacturing process is not good, for example, the casting quality and machining accuracy are unqualified; or the conveyed liquid is corrosive, and the impeller flow path is eroded and corroded, causing the impeller to be eccentric. The number of blades of the centrifugal pump impeller, outlet angle, wrap angle, whether the radial distance between the throat tongue and the impeller outlet edge is appropriate, etc. In use, between the impeller mouth ring and the pump body mouth ring of the centrifugal pump, between the inter-stage bushing and the diaphragm bushing, the initial rubbing gradually becomes mechanical friction and wear, which will aggravate the vibration of the centrifugal pump.

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