1. the ten major causes of centrifugal pump vibration - shaft
Pumps with long shafts are prone to insufficient shaft stiffness, excessive deflection, and poor straightness of the shaft system, resulting in contact and friction between the moving parts (drive shaft) and stationary parts (sliding bearings or gland), causing vibration. In addition, a long pump shaft is greatly affected by the impact of flowing water in the water tank, increasing the vibration of the lower part of the pump. Excessive clearance at the end of the shaft disc or improper adjustment of axial working displacement can cause low-frequency axial displacement and lead to bearing vibration. Eccentricity of rotating shaft can cause bending vibration of the shaft.
2. ten major causes of centrifugal pump vibration - foundation and pump support.
The contact fixing form between the drive device frame and the foundation is not good, and the ability of the foundation and motor system to absorb, transmit, and isolate vibrations is poor, resulting in excessive vibration of both the foundation and motor. The pump foundation becomes loose, or the pump unit forms an elastic foundation during installation, or the stiffness of the foundation is weakened due to oil immersion water bubbles. This will cause another critical speed with a phase difference of 1800 from vibration for the pump, thereby increasing its vibration frequency. If the increased frequency is close to or equal to a certain external factor frequency, it will increase the amplitude of pump vibration. In addition, loosening of anchor bolts on the foundation reduces constraint stiffness and exacerbates motor vibration.
3. Ten major causes of centrifugal pump vibration - coupling
The circumferential spacing of the coupling connecting bolts is poor, and symmetry is disrupted; lengthening the eccentricity of the coupling will generate eccentric forces; the taper degree of the coupling is beyond tolerance; poor static or dynamic balance of the coupling; excessive fit between elastic pins and couplings causes loss of elastic adjustment function, resulting in poor alignment of the couplings; excessive clearance between couplings and shafts; mechanical wear on the coupling rubber ring leads to decreased performance in fitting with the rubber ring; varying quality of transmission bolts used on couplings. These reasons can all cause vibration.
4. Ten major factors causing centrifugal pump vibration - factors related to the pump itself
The asymmetric pressure field generated by the impeller rotation; vortex in the suction pool and inlet pipe; occurrence and disappearance of vortices inside the impeller, volute casing, and guide vanes;
vibration caused by vortex formation due to partially open valves; uneven outlet pressure distribution due to limited number of impeller blades; flow separation inside the impeller; surging; pulsating pressure in the flow passage; cavitation; water flowing in the pump body causing friction and impact, such as water hitting the leading edge of diffuser vanes, resulting in vibration; boiler feed pumps transporting high-temperature water are prone to cavitation-induced vibrations；
pressure pulsation inside the pump body, mainly caused by excessive clearance between pump impeller sealing rings and pump body sealing rings, leading to large leakage loss within the pump body, severe backflow, resulting in imbalance of rotor axial force and pressure pulsation which enhances vibration. Additionally, for hot water pumps used for transporting hot water.
if there is uneven preheating before startup or abnormal operation of sliding pin system of the pump shafts causing thermal expansion of the pump assembly can induce severe vibrations during startup stage；
if internal stresses from thermal expansion cannot be released within the pump body it will cause changes in stiffness of shaft support system. When this changed stiffness becomes a multiple integer relationship with system natural frequency (resonance), resonance occurs.
5. The ten main causes that lead to centrifugal pump vibrations - motor
The motor structural components are loose, the bearing positioning device is loose, the iron core silicon steel sheet is too loose, and the decrease in support stiffness caused by bearing wear can cause vibration. Quality eccentricity, rotor bending or uneven mass distribution of the rotor can cause excessive static and dynamic balance deviation.
In addition, there are fractures in the squirrel cage bars of squirrel-cage motors' rotors, causing imbalance between the magnetic field force exerted on the rotor and the rotational inertia force of the rotor, as well as vibrations caused by missing phases in the motor or unbalanced power supply to each phase.
The stator winding of the motor may have an imbalance in resistance between different phases due to poor quality control during installation procedures, resulting in an uneven magnetic field and generating unbalanced electromagnetic forces that induce vibrations.
6: Ten major causes of centrifugal pump vibration - pump selection and variable operating conditions.
Each pump has its own rated operating conditions, and whether the actual operating conditions match the design conditions has a significant impact on the dynamic stability of the pump.
The water pump operates relatively stably under design conditions, but when operating under variable conditions, vibration increases due to the radial force generated in the impeller.
Improper selection of a single pump or parallel operation of two mismatched pumps can also cause pump vibration.
7. Ten major causes of centrifugal pump vibration - bearings and lubrication
The low stiffness of the bearing will cause a decrease in the first critical speed and result in vibration. In addition, poor performance of the guide bearing leads to poor wear resistance, inadequate fixation, and excessive clearance between the shaft and bushing, which can also cause vibration.
The wear of thrust bearings and other rolling bearings will intensify longitudinal jumping vibration and bending vibration of the shaft. Improper selection, deterioration or excessive impurity content of lubricating oil, as well as lubrication failure caused by blocked lubrication pipelines, can worsen the operating conditions of bearings and trigger vibrations.
Self-excitation of sliding bearing oil film in electric motors can also generate vibrations.
8. Ten major causes of centrifugal pump vibrations - pipes and their installation fixation
The stiffness of the outlet pipeline support for the pump is insufficient, resulting in excessive deformation and causing downward pressure on the pump body, leading to misalignment between the pump body and motor.
During installation, there was excessive resistance in the pipeline, resulting in high internal stress when connecting the inlet and outlet pipelines with the pump.
The loose connection of inlet and outlet pipelines leads to decreased or even failed restraining stiffness. The outlet flow channel is completely fractured, with fragments getting stuck in the impeller.
The pipeline is not smooth, such as having air pockets at the water outlet.
The discharge valve may be loose or not open properly. There may be air intake at the water inlet, causing uneven flow field and pressure fluctuations. These reasons can directly or indirectly cause vibration in both pumps and pipelines.
9. Ten major causes of centrifugal pump vibration - Fit between components
The concentricity of the motor shaft and pump shaft is poor; the coupling used at the connection between the motor and transmission shaft has poor concentricity; the wear of the design clearance between moving and static parts (such as impeller blades and volute) increases;
there is excessive gap between the intermediate bearing support and pump casing; inappropriate clearance of sealing rings causing imbalance; uneven gaps around the sealing ring, such as no groove for volute or baffle, can cause this situation. These unfavorable factors can all cause vibration.
10, ten major causes of centrifugal pump vibration - impeller.
The impeller of the centrifugal pump is eccentric in mass.
The quality control during the manufacturing process of the impeller is not good, for example, casting quality and processing accuracy are unqualified; or the conveyed liquid is corrosive, causing erosion on the impeller flow path and resulting in eccentricity of the impeller.
Factors such as the number of blades, outlet angle, wrap angle, throat baffle, and radial distance between throat baffle and impeller outlet edge of the centrifugal pump impeller need to be appropriate.
During use, there will be gradual transition from initial contact to mechanical friction wear between the impeller sealing ring and pump body sealing ring as well as between inter-stage bushing and partition plate bushing, which will exacerbate vibration in the centrifugal pump.
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