Ten Causes Of Centrifugal Pump Vibration

1.The ten causes of centrifugal pump vibration - shaft

The pump with a long shaft is prone to insufficient shaft stiffness, too large deflection, and poor straightness of the shafting, resulting in friction between the moving part (transmission shaft) and the static part (sliding bearing or mouth ring), forming vibration. In addition, the pump shaft is too long, which is greatly affected by the impact of flowing water in the pool, and the vibration of the underwater part of the pump is increased. Excessive clearance of the balance disc at the shaft end, or improper adjustment of the axial working channeling momentum, will cause the shaft low-frequency channeling, resulting in bearing vibration. The eccentricity of the rotating shaft will cause the bending vibration of the shaft.

 

2.Ten 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 the motor system to absorb, transmit and isolate vibration is poor, resulting in the vibration of the foundation and the motor exceeding the standard. The pump foundation is loose, or the pump unit forms an elastic foundation during the installation process, or the foundation stiffness is weakened due to the oil-soaked water bubble, the pump will produce another critical speed with the vibration phase difference of 1800, so that the pump vibration frequency increases, if the increased frequency is close to or equal to the frequency of an external factor, it will increase the amplitude of the pump. In addition, the foundation bolt is loose, resulting in reduced constraint stiffness, which will aggravate the vibration of the motor.

 

3.Ten causes of centrifugal pump vibration - coupling

The circular spacing of the coupling bolt is not good, and the symmetry is broken. Coupling extension eccentricity will produce eccentric force; Coupling taper out; Coupling static balance or dynamic balance is not good; The coupling of the elastic pin and the coupling is too tight, so that the elastic pin loses the elastic adjustment function and the coupling can not be well aligned; The clearance between the coupling and the shaft is too large; The mechanical wear of coupling rubber ring leads to the deterioration of coupling rubber ring mating performance; The quality of the transmission bolts used on the coupling varies from one to the other. All of these causes cause vibration.

 

4.Ten causes of centrifugal pump vibration - the pump itself

Asymmetric pressure field generated when the impeller rotates; Eddy currents in suction pool and inlet pipe; The occurrence and disappearance of vortices inside the impeller, the vortex shell and the guide blade; The vibration caused by the whirlpool caused by the valve being ajar; The uneven distribution of outlet pressure due to the limited number of impeller blades; Deflow in the impeller; Surge; Pulsating pressure in the runner; Cavitation; When water flows in the pump body, it has friction and impact on the pump body. For example, the water hits the leading edge of the baffle tongue and the guide blade, causing vibration. The boiler feed pump transporting high temperature water is prone to cavitation vibration. The pressure pulsation in the pump body is mainly the seal ring of the pump impeller, and the gap of the seal ring of the pump body is too large, resulting in large leakage loss in the pump body and serious reflux, which will cause the imbalance of the axial force of the rotor and pressure pulsation, which will enhance the vibration. In addition, for the hot water pump transporting hot water, if the preheating of the pump is uneven before starting, or the sliding pin system of the pump is not working normally, resulting in the thermal expansion of the pump group, will induce violent vibration during the start-up stage; When the internal stress of the pump body from thermal expansion and other aspects cannot be released, it will cause the stiffness of the rotating shaft support system to change. When the changed stiffness is an integral multiple of the angular frequency of the system, resonance will occur.

 

5.Ten causes of centrifugal pump vibration - motor

 

The structural parts of the motor are loose, the bearing positioning device is loose, the silicon steel sheet of the iron core is too loose, and the support stiffness of the bearing is reduced due to wear, which will cause vibration. Mass eccentricity, rotor bending or mass distribution problems lead to uneven rotor mass distribution, resulting in static and dynamic balance excess. 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 rotary inertia force of the rotor to be unbalanced and cause vibration, the motor phase shortage, the imbalance of each phase power supply and other reasons can also cause vibration. The stator windings of the motor, due to the operation quality problems of the installation process, cause the resistance between the phases of the windings to be unbalanced, resulting in an uneven magnetic field, resulting in an unbalanced electromagnetic force, which becomes an exciting force to cause vibration.

 

6.Ten causes of centrifugal pump vibration - pump selection and variable operating conditions

Each pump has its own rated working conditions, the actual operating conditions and design conditions are consistent, has an important impact on the dynamic stability of the pump. The pump runs stably under the design condition, but the vibration increases because of the radial force in the impeller under the variable operating condition. Improper selection of a single pump, or two types of mismatched pumps parallel. All of this causes the pump to vibrate.

 

7.Ten causes of centrifugal pump vibration - bearing and lubrication

The stiffness of the bearing is too low, which will cause the first critical speed to decrease and cause vibration. In addition, the poor performance of the guide bearing leads to poor wear resistance, poor fixing, bearing clearance is too large, and it is easy to cause vibration; The wear of thrust bearings and other rolling bearings will aggravate the longitudinal and bending vibration of the shaft. Lubrication failure caused by improper lubricating oil selection, deterioration, excessive impurity content and poor lubrication pipeline will cause deterioration of bearing working conditions and cause vibration. The self-excited oil film of motor plain bearing will also produce vibration.

 

8.Ten causes of centrifugal pump vibration - pipeline and its installation fixed

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The stiffness of the pump outlet pipe support is not enough, and the deformation is too large, which causes the pipeline to press down on the pump body, making the pump body and the motor neutral damage; The strength of the pipeline is too large during the installation process, and the internal stress is large when the import and export pipeline is connected with the pump; The inlet and outlet pipelines are loosened, the restraint stiffness decreases or even fails; All parts of the outlet runner were broken, and the fragments stuck to the impeller. The pipeline is not smooth, such as the water outlet has air bags; The outlet valve falls off, or does not open; The inlet has air intake, uneven flow field, pressure fluctuation. These causes will directly or indirectly lead to pump and pipeline vibration.

 

9.Ten causes of centrifugal pump vibration - the coordination between parts

The concentricity of motor shaft and pump shaft is out of whack; The coupling is used at the connection of the motor and the drive shaft, and the concentricity of the coupling is out of tolerance; The wear of the design gap between the dynamic and static parts (such as between the blade of the impeller and the mouth ring) is increased; The gap between the intermediate bearing bracket and the pump barrel exceeds the standard; The seal ring gap is not suitable, resulting in an imbalance; This occurs when the gap around the seal ring is uneven, such as when the mouth ring is not slotted or the partition is not slotted. These adverse factors can cause vibration.

 

10.Ten causes of centrifugal pump vibration - impeller

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Centrifugal pump impeller mass eccentricity. The quality control of the impeller manufacturing process is not good, for example, the casting quality and processing accuracy are not qualified; Or the liquid transported is corrosive, and the impeller flow path is eroded, resulting in eccentricity of the impeller. Centrifugal pump impeller blade number, outlet Angle, envelope Angle, throat tongue and impeller outlet edge of the radial distance is appropriate. Between the impeller mouth ring and the pump body mouth ring of the centrifugal pump, between the stage bushing and the separator bushing, the initial friction gradually becomes mechanical friction and wear, which will aggravate the vibration of the centrifugal pump.