1： Shaft
（1）: If the shaft of the pump is very long, it is easy to have insufficient shaft stiffness,too large deflection and poor straightness of the shaft system resulting in friction between moving parts (transmission shaft) and static parts (sliding bearing or mouth ring), forming vibration.
（2）: In addition, the pump shaft is too long, which is greatly affected by the impact of flowing water in the pool, so that the vibration of the underwater part of the pump increases.
（3）: If the balance plate gap at the end of the shaft is too large, or the axial working displacement is not adjusted properly, the low-frequency displacement of the shaft will be caused, resulting in the vibration of the bearing bush.
（4）: The eccentricity of the rotating shaft will cause the bending vibration of the shaft
1: The fixed form of contact between the driving device frame and the foundation is not good, and the absorption, transmission and isolation ability of the foundation and the motor system are poor, resulting in the vibration of both the foundation and the motor exceeding the standard.
2: Foundation and pump support
（1）: The fixed form of contact between the driving device frame and the foundation is not good, and the absorption, transmission and isolation ability of the foundation and the motor system are poor, resulting in the vibration of both the foundation and the motor exceeding the standard.
（2）: If the pump foundation is loose, or the pump unit forms an elastic foundation during installation, or the foundation rigidity is weakened due to the oil immersed water bubble, another critical speed of 1800 phase difference between the pump and the vibration will be generated, thus increasing the vibration frequency of the pump,
（3）:If the increased frequency is close to or equal to the frequency of an external factor, the amplitude of the pump will increase. In addition, the foundation anchor bolts loose, resulting in reduced constraint stiffness, will make the vibration of the motor intensified.
3: Coupling
(1) : The circumferential spacing of the coupling connecting bolts is poor, and the symmetry is damaged; the eccentric force will be produced when the coupling extension is eccentric;
(2) : The static or dynamic balance of the coupling is not good;
(3) : The fit between the elastic pin and the coupling is too tight, which makes the elastic pin lose the elastic adjustment function and the coupling can not be well aligned;
(4) : The fit clearance between the coupling and the shaft is too large, and the mechanical wear of the coupling rubber ring leads to the decrease of the fit performance of the coupling rubber ring;
The quality of the transmission bolts used on the coupling is not equal to each other.
All of these causes cause vibration.
4: Factors of the pump itself
(1): The unsymmetrical pressure field produced by impeller rotation;
(2):Vortex in suction basin and inlet pipe; occurrence and disappearance of vortex in impeller, volute shell and guide vane;
(3): The vibration caused by vortex caused by half opening of valve;
(4): The uneven distribution of outlet pressure due to the limited number of impeller blades; the flow separation in impeller;
(5):Surge; fluctuating pressure in flow passage;
(6): cavitation;
(7):When water flows in the pump body, there will be friction and impact on the pump. For example, water flow will impact the front edge of the tongue and guide vane, causing vibration;
(8):The boiler feed water pump conveying high-temperature water is prone to cavitation vibration; the pressure pulsation in the pump body is mainly caused by the sealing ring of the pump impeller and the excessive clearance of the sealing ring of the pump body, which results in large leakage loss in the pump body and serious return flow, thus causing the imbalance of the axial force of the rotor and the pressure pulsation, which will increase the vibration.
(9):In addition, for the hot water pump that delivers hot water, if the preheating of the pump is uneven before starting, or the operation of the sliding pin system of the pump is abnormal, resulting in the thermal expansion of the pump set, it will cause severe vibration in the starting stage;
(10): If the internal stress of the pump body from thermal expansion can not be released, it will cause the change of the stiffness of the shaft support system. When the changed stiffness is integral multiple of the system angular frequency, resonance will occur.
5: Motor
(1): The motor structure is loose, the bearing positioning device is loose, the silicon steel sheet of the iron core is too loose, and the bearing's support stiffness decreases due to wear, which will cause vibration.
(2): The unbalanced distribution of rotor mass caused by eccentric mass, bending of rotor or mass distribution problems results in the excessive static and dynamic balance.
(3): In addition, the squirrel cage bars of the rotor of the squirrel cage motor are broken, resulting in the unbalance of the magnetic field force and the rotating inertia force of the rotor, resulting in the vibration.
(4): The motor is lack of phase, the power supply of each phase is unbalanced and other reasons can also cause the vibration.
(5): Due to the operation quality problems in the installation process of the stator winding of the motor, the resistance between the windings of each phase is unbalanced, resulting in the uneven magnetic field and the unbalanced electromagnetic force, which becomes the excitation force and causes the vibration.
6: Pump selection and variable operating conditions
(1): Each pump has its own rated operating point.
Whether the actual operating conditions are consistent with the designed operating conditions has an important impact on the dynamic stability of the pump.
(2): The pump operates relatively stably under the design conditions, but when running under variable conditions.
The vibration is increased due to the radial force generated by the impeller;
(3): the single pump is not selected properly, or two models Mismatched pumps are connected in parallel. These will cause the pump to vibrate.
7: Bearing and lubrication
(1): Too low stiffness of the bearing will reduce the first critical speed and cause vibration.
(2): In addition, the poor performance of the guide bearing leads to poor wear resistance, poor fixation, too large bearing bush clearance, and also easy to cause vibration;
(3):while the wear of the thrust bearing and other rolling bearings will make the longitudinal vibration and bending vibration of the shaft increase at the same time.
(4): Improper selection of lubricating oil, deterioration, excessive impurity content and lubrication failure caused by poor lubrication pipeline will cause deterioration of bearing working condition and vibration.
(5):The self-excited oil film of motor sliding bearing will also produce vibration.
8: Pipeline and its installation and fixation
(1): The outlet pipe support of the pump is not rigid enough, and the deformation is too large, which causes the pipe to press down on the pump body, causing the neutral damage of the pump body and the motor;
(2)：During the installation process, the pipeline is too strong, and the internal stress of the inlet and outlet pipelines is large when they are connected with the pump;
(3)：The inlet and outlet pipelines are loose, and the constraint stiffness drops or even fails;
(4)：The outlet channel is partially broken, and the debris gets stuck in the impeller;
(5): The pipeline is not smooth, such as the air bag at the water outlet;
(6) :The water outlet valve falls off or is not opened;
(7): The water inlet has air inlet, the flow field is uneven, and the pressure fluctuates.
These causes will directly or indirectly lead to pump and pipeline vibration.
9: Mate between components
(1): The concentricity of motor shaft and pump shaft is out of tolerance; coupling is used at the connection of motor and transmission shaft, and the concentricity of coupling is out of tolerance;
(2): The wear of the design clearance between the dynamic and static parts (such as between the impeller and the ring) becomes larger;
(3): The clearance between the intermediate bearing bracket and the pump barrel exceeds the standard; the clearance between the sealing ring is improper, which causes imbalance; the clearance around the sealing ring is uneven, such as the mouth ring is not in the groove or the baffle is not in the groove, which will happen.
These adverse factors can cause vibration.
10:Impeller
(1): The quality of the centrifugal pump impeller is eccentric.
(2): The quality control in the manufacturing process of the impeller is not good, for example, the casting quality and machining accuracy are unqualified;
(3): Whether the number of blades, exit angle, wrap angle, throat tongue and the radial distance between the impeller exit edge of the centrifugal pump impeller are appropriate.
(4): The use of the middle impeller ring ring and the pump body ring ring of the centrifugal pump, between the interstage bushing and the partition bushing, from the initial rubbing, gradually becomes mechanical friction and wear, which will exacerbate the centrifugation Pump vibration.
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