10 major reasons for centrifugal pump vibration

In rotating equipment and flowing media, low-intensity mechanical vibration is inevitable. But just like a cough, if it is not cured for a long time, it will inevitably lead to a disaster... The following is a detailed introduction to the top ten reasons for centrifugal pump vibration, hoping to help the user unit.

1. The top ten reasons for centrifugal pump vibration-shaft
Pumps with very long shafts are prone to insufficient shaft stiffness, excessive deflection, and poor shaft straightness, causing friction between the moving parts (drive shafts) and the static parts (sliding bearings or mouth rings), resulting in vibration. In addition, the pump shaft is too long, which is greatly affected by the impact of flowing water in the pool, increasing 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 low-frequency movement of the shaft, resulting in bearing vibration. The eccentricity of the rotating shaft will cause bending vibration of the shaft.

2. The top ten reasons for centrifugal pump vibration-foundation and pump bracket
The contact fixing form between the drive frame and the foundation is not good, and the foundation and motor system have poor ability to absorb, transmit, and isolate vibration, resulting in excessive vibration of the foundation and motor. If the foundation of the water pump is loose, or the water pump unit forms an elastic foundation during installation, or the foundation stiffness is weakened due to oil-immersion bubbles, the water pump will generate 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 a certain external factor, the amplitude of the water 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. Ten major causes of centrifugal pump vibration-coupling
The circumferential spacing of the coupling connection bolts is poor, and 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 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; the quality of the transmission bolts used on the coupling is not equal. These reasons will cause vibration.

4. The ten major reasons for centrifugal pump vibration - factors of the pump itself
The asymmetric pressure field generated when the impeller rotates; the vortex in the suction pool and the inlet pipe; the occurrence and disappearance of the vortex inside the impeller and the volute and guide vane; the vibration caused by the vortex caused by the half-open valve; the uneven distribution of outlet pressure due to the limited number of impeller blades; the flow separation in the impeller; surge; the pulsating pressure in the flow channel; cavitation; the water flows in the pump body, which will cause friction and impact on the pump body, such as the water flow hitting the leading edge of the baffle and the guide vane, causing vibration; the boiler feed pump that transports high-temperature water is prone to cavitation vibration; the pressure pulsation in the pump body is mainly the pump impeller sealing ring. The gap of the pump body sealing ring is too large, resulting in large leakage losses in the pump body and serious backflow, which in turn causes the imbalance of the rotor axial force and pressure pulsation, which will enhance the vibration.

In addition, for 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. Ten major causes of centrifugal pump vibration-motor
Loose motor structural parts, loose bearing positioning devices, too loose iron core silicon steel sheets, and reduced support stiffness due to wear of the bearing will cause vibration. Mass eccentricity, rotor bending or mass distribution problems cause uneven distribution of rotor mass, resulting in excessive static and dynamic balance.

In addition, the 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. Motor phase loss and unbalanced power supply of each phase 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. The ten major causes of centrifugal pump vibration - water 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 water 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 selection of a single pump, or two unmatched pumps in parallel. These will cause pump vibration.

7. The ten major causes of centrifugal pump vibration - bearings and lubrication
The stiffness of the bearing 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 can also easily cause vibration; and 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.

Eight, the ten major reasons for the vibration of the centrifugal pump-pipeline and its installation and fixation
The outlet pipe bracket of the pump is not rigid enough and deforms too much, causing the pipe to press down on the pump body, which destroys the alignment of the pump body and the motor; the pipe is too stiff during the installation process, and the internal stress is large when the inlet and outlet pipes are connected to the pump; the inlet and outlet pipelines are loose, and the constraint stiffness decreases or even fails; the outlet flow channel is completely broken, and the fragments are stuck in the impeller; the pipeline is not smooth, such as air bags at the outlet; the outlet valve falls off or is not opened; there is air intake at the inlet, uneven flow field, and pressure fluctuations. These reasons will directly or indirectly cause vibration of the pump and pipeline.

9. The ten major reasons for centrifugal pump vibration - the fit between parts
The concentricity of the motor shaft and the pump shaft is out of tolerance; the coupling is used at the connection between the motor and the transmission shaft, and 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 between the seal ring is not appropriate, causing imbalance; the gap around the seal ring is uneven, such as the mouth ring is not in the groove or the partition is not in the groove, which will happen. These unfavorable factors can cause vibration.

Ten. The ten major reasons for centrifugal pump vibration - impeller
The quality of the centrifugal pump impeller is eccentric. The quality control is not good during the manufacturing process of the impeller, for example, the casting quality and processing accuracy are not up to standard; or the liquid being transported is corrosive, and the impeller flow channel is eroded and corroded, causing the impeller to be eccentric. The number of blades, outlet angle, wrap angle, and radial distance between the throat baffle and the impeller outlet edge of the centrifugal pump impeller are appropriate. During use, the friction between the impeller mouth ring and the pump body mouth ring of the centrifugal pump, and between the interstage bushing and the partition bushing, gradually changes to mechanical friction and wear, which will aggravate the vibration of the centrifugal pump.

HL Petroleum is a Chinese centrifugal pump manufacturer. Its main equipment includes Mission Centrifugal Pump, Centrifugal Sand Pump, Mud Agitator, Spray Pump, Centrifugal Pump Spare Parts and various oil drilling solids control equipment. If you have demand for such products, please contact us.