Whether the pump vibrates abnormally is an important indicator for evaluating whether the quality of the water 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 movement, dynamic and static balance, high-speed rotating parts, etc., which may affect the stability of the water pump. Let's give you a comprehensive analysis of the reasons for the vibration of the water pump. 10 reasons for vibration: 1. The shaft of the pump is very long. It is easy to cause friction between the moving parts (drive shaft) and the static parts (sliding bearings or mouth rings) due to insufficient stiffness of the water pump, too much deflection, poor straightness of the shaft system, etc., resulting in vibration of the water pump. 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 multi-stage pump. The gap of the pump shaft balance plate is too large, or the axial working movement is improperly adjusted, which will also cause low-frequency movement of the shaft, resulting in bearing vibration. The eccentricity of the rotating shaft will also cause bending vibration of the shaft.
2. The contact fixing form between the foundation and the pump bracket drive device frame and the foundation is not good. The foundation and motor system have poor ability to absorb, transmit and isolate vibration, resulting in excessive vibration of the foundation and motor. The water pump foundation is loose, or the water pump unit forms an elastic foundation during installation, or the foundation stiffness is weakened due to oil immersion and water bubbles. The water pump will produce another critical speed with a vibration phase difference of 1800, thereby increasing the vibration frequency of the water pump. If the increased frequency is close to or equal to the frequency of an external factor, the amplitude of the multi-stage pump will increase. In addition, the foundation anchor bolts are loose, resulting in a decrease in constraint stiffness, which will intensify the vibration of the motor. 3. The circumferential spacing of the coupling connection bolts is poor, the symmetry is destroyed, the coupling extension section is eccentric, which will generate eccentric force, the coupling taper is out of tolerance, the coupling static balance or dynamic balance is not good, the elastic pin and the coupling are too tight, so that the elastic column pin loses its elastic adjustment function, causing the coupling to not be well aligned, the matching clearance between the coupling and the shaft is too large, the mechanical wear of the coupling rubber ring leads to a decrease in the matching performance of the coupling rubber ring, and the quality of the transmission bolts used on the coupling is not equal. These reasons will cause vibration of the multi-stage pump.
4. Factors of the water pump itself: asymmetric pressure field generated when the impeller rotates; vortex in the water suction pool and inlet pipe; occurrence and disappearance of vortex inside the impeller, volute, and guide vane; vibration caused by vortex caused by half-open valve; uneven outlet pressure distribution due to limited number of impeller blades; flow separation in the impeller; surge; pulsating pressure in the flow channel; cavitation; water flows in the pump body, causing friction and impact on the pump body, such as water flow hitting the leading edge of the baffle and guide vane, causing vibration; boiler feed pumps that transport high-temperature water are prone to cavitation vibration; pressure pulsation in the pump body, mainly the pump impeller sealing ring, the gap of the pump body sealing ring is too large, resulting in large leakage loss in the pump body, severe backflow, and then causing imbalance of rotor axial force and pressure pulsation, which will enhance vibration.
In addition, for stainless steel hot water pumps that transport hot water, if the preheating of the pump is uneven before starting, or the water pump sliding pin system does not work properly, causing thermal expansion of the pump group, it will induce severe vibration during the startup phase; if the internal stress of the pump body from thermal expansion and other aspects cannot be released, it will cause the stiffness of the shaft support system to change. When the stiffness after the change is an integer multiple of the system angular frequency, resonance occurs. 5. The looseness of the motor structure, the looseness of the bearing positioning device, the looseness of the core silicon steel sheet, and the decrease in the support stiffness of the bearing due to wear will cause vibration. The uneven distribution of the rotor mass caused by mass eccentricity, rotor bending or mass distribution problems causes the static and dynamic balance to exceed the standard. In addition, the squirrel cage bars of the squirrel cage motor rotor are broken, causing the magnetic field force on the rotor and the rotational inertia force of the rotor to be unbalanced, causing vibration. The motor is missing a phase, and the power supply of each phase is unbalanced. Other reasons can also cause vibration. The stator winding of the motor, due to the quality of the operation during the installation process, causes the resistance between the phase windings to be unbalanced, resulting in an uneven magnetic field and an unbalanced electromagnetic force, which becomes an exciting force and causes vibration. 6. Pump selection and variable operating conditions Each pump has its own rated operating point. Whether the actual operating conditions are consistent with the design conditions has an important impact on the dynamic stability of the pump. The pump operates relatively stably under the design conditions, but when it operates under variable conditions, the vibration is increased due to the radial force generated in the impeller, improper single pump selection, or two unmatched pumps in parallel. These will cause vibration in multi-stage pumps.
7. The stiffness of the bearings and lubricating bearings is too low, which will cause the first critical speed to decrease and cause vibration. In addition, poor guide bearing performance leads to poor wear resistance, poor fixation, and excessive bearing clearance, which are also prone to vibration. The wear of thrust bearings 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 unsmooth lubrication pipelines will cause the bearing working condition to deteriorate and cause vibration. The self-excitation of the oil film of the motor sliding bearing will also cause vibration.
8. The outlet pipe bracket of the pipeline and its installation fixed pump is not rigid enough and deforms too much, causing the pipeline to press down on the pump body, which destroys the alignment of the pump body and the motor. The pipeline is too stiff during installation. The internal stress is large when the inlet and outlet pipelines are connected to the pump. The inlet and outlet pipelines are loose, the constraint stiffness decreases or even fails, the outlet flow channel is completely broken, the debris is stuck in the impeller, the pipeline is unsmooth, such as air bags at the outlet, the outlet valve falls off, or is not opened, there is air intake at the inlet, the flow field is uneven, and the pressure fluctuates. These reasons will directly or indirectly cause vibration of multi-stage pumps and pipelines. 9. 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. The concentricity of the coupling is out of tolerance. The wear of the design clearance between the dynamic and static parts (such as between the impeller and the mouth ring) increases. The clearance between the intermediate bearing bracket and the pump barrel exceeds the standard. The gap of the sealing ring is not appropriate, resulting in imbalance. The gap around the sealing ring is uneven. For example, the mouth ring is not in the groove or the partition is not in the groove. This will happen. These unfavorable factors can cause vibration of multi-stage pumps. 10. The impeller of the impeller pump is eccentric. The quality control during the manufacturing process of the impeller is not good. For example, the casting quality and processing accuracy are not up to standard, or the conveyed liquid is corrosive, and the impeller flow channel is eroded and corroded, resulting in eccentricity of the impeller. Whether the number of blades, outlet angle, wrap angle, and radial distance between the throat baffle and the impeller outlet edge of the water pump impeller are appropriate, etc. During use, the initial friction between the impeller mouth ring and the pump body mouth ring of the multistage pump, and between the interstage bushing and the partition bushing, gradually turns into mechanical friction and wear, which will aggravate the vibration of the multistage pump.
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