The vibration of various components of the pump unit, from the hydraulic and mechanical structure design of the pump to the installation, operation, and maintenance of the pump, several measures to reduce pump vibration are proposed. The results show that ensuring that the structural dimensions and accuracy of pump components are compatible with the hydraulic characteristics of the pump such as its non overload performance; Ensure that the actual operating point of the pump matches the design operating point of the pump; Ensure consistency between machining accuracy and design accuracy; Ensure the consistency between the installation quality of components and their operational requirements; Ensuring consistency between maintenance quality and wear patterns of components can reduce pump vibration. The main hazards caused by excessive vibration include: causing the pump unit to not operate normally; Causing vibration of the motor and pipeline, causing machine damage and personal injury; Causing damage to bearings and other components; Causing looseness of connecting parts, foundation cracks, or motor damage; Causing loose or damaged pipe fittings or valves connected to the water pump; Formation of vibration noise. The causes of pump vibration are manifold. The rotating shaft of a pump is generally directly connected to the shaft of the drive motor, causing the dynamic performance of the pump and the dynamic performance of the motor to interfere with each other; There are many high-speed rotating parts, and dynamic and static balance can meet the requirements; The components that interact with the fluid are greatly affected by the water flow condition; The complexity of fluid motion itself is also a factor limiting the stability of pump dynamic performance.
1.1 Motor
The motor structure is loose, the bearing positioning device is loose, the iron core silicon steel sheet is too loose, and the bearing stiffness decreases due to wear, which can cause vibration. Mass eccentricity, rotor bending, or uneven rotor mass distribution caused by mass distribution problems, resulting in excessive static and dynamic balance. In addition, the squirrel cage bar of the rotor of a squirrel cage motor is broken, resulting in an imbalance between the magnetic field force applied to the rotor and the rotational inertia force of the rotor, causing vibration, as well as a lack of phase in the motor and an imbalance in the power supply of each phase. Due to operational quality issues in the installation process of the motor stator winding, the resistance between the windings of each phase is unbalanced, resulting in uneven magnetic fields and unbalanced electromagnetic forces, which become excitation forces that cause vibration.
1.2 Foundation and pump support
The contact and fixation method used between the drive device frame and the foundation is not good, and the foundation and motor system have poor vibration absorption, transmission, and isolation capabilities, 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 and water bubbles, the water pump will generate another critical rotational speed with a phase difference of 1800 from the vibration, 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 water pump will increase. In addition, the loosening of foundation anchor bolts leads to a reduction in the restraint stiffness, which can exacerbate the vibration of the motor.
1.3 Coupling
The circumferential spacing of the coupling connecting bolts is poor, and the symmetry is damaged; The eccentric coupling extension will generate eccentric force; The taper of the coupling exceeds the tolerance; Poor static or dynamic balance of the coupling; The tight fit between the elastic pin and the coupling causes the elastic pin to lose its elastic adjustment function, resulting in poor alignment of the coupling; The fit clearance between the coupling and the shaft is too large; The mechanical wear of the coupling rubber ring results in a decrease in the fitting performance of the coupling rubber ring; The quality of the transmission bolts used on the coupling varies from one another. These causes can cause vibration.
1.4 Centrifugal pump impeller
① The impeller mass of a centrifugal pump is eccentric. Poor quality control during impeller manufacturing, such as unqualified casting quality and machining accuracy; Or the liquid conveyed is corrosive, and the impeller flow path is eroded and corroded, resulting in eccentric impeller.
② Whether the number of blades, outlet angle, wrap angle, radial distance between throat spacer and impeller outlet edge of centrifugal pump impeller are appropriate.
③ During use, the initial friction between the impeller ring and the pump body ring of the centrifugal pump, as well as between the interstage bushing and the diaphragm bushing, gradually becomes mechanical friction and wear, which will intensify the vibration of the centrifugal pump.
1.5 Transmission shaft and its auxiliary parts
Pumps with long shafts are prone to insufficient shaft stiffness, large deflections, and poor shafting straightness, resulting in friction between moving parts (transmission shafts) and stationary parts (sliding bearings or mouth rings), resulting in vibration. In addition, the pump shaft is too long and is greatly affected by the impact of flowing water in the pool, which increases the vibration of the underwater part of the pump. Excessive clearance of the balance disk at the shaft end, or improper adjustment of the axial working displacement, can cause low-frequency shaft movement, leading to bearing bush vibration. The eccentricity of the rotating shaft can cause bending vibration of the shaft.
1.6 Pump selection and off-design operation
Each pump has its own rated operating point, and whether the actual operating conditions match the design conditions has an important impact on the dynamic stability of the pump. The pump operates relatively stably under design conditions, but when operating under variable conditions, the vibration increases due to the radial force generated in the impeller; Improper selection of single pump or parallel connection of two mismatched pumps. These can cause vibration of the pump.
1.7 Bearing and lubrication
If the stiffness of the bearing is too low, it will cause a decrease in the critical speed and cause vibration. In addition, poor performance of the guide bearing can lead to poor wear resistance, poor fixation, and excessive bearing clearance, which can also easily cause vibration; The wear of thrust bearings and other rolling bearings can exacerbate both longitudinal and flexural vibrations of the shaft. Improper selection of lubricating oil, deterioration, excessive impurity content, and lubrication failures caused by clogged lubrication pipes can cause deterioration in bearing conditions and cause vibration. The self-excitation of the oil film of the motor sliding bearing can also generate vibration.
1.8 Pipeline and its installation and fixation
The outlet pipe support of the pump is not rigid enough and deformed too much, causing the pipe to press down on the pump body, causing damage to the neutral of the pump body and motor; The pipeline is too stiff during installation, resulting in high internal stress when connecting the inlet and outlet pipelines to the pump; The inlet and outlet pipelines are loose, and the constraint stiffness decreases or even fails; The outlet flow passage is completely broken and debris is stuck in the impeller; The pipeline is not smooth, such as air bags at the water outlet; The water outlet valve falls off or does not open; There is intake air at the water inlet, the flow field is uneven, and the pressure fluctuates. These reasons can directly or indirectly cause vibration of the pump and pipeline.
1.9 Coordination between parts
The concentricity of the motor shaft and the pump shaft exceeds the tolerance; A coupling is used at the connection between the motor and the transmission shaft, and the concentricity of the coupling exceeds the tolerance; The wear of the design gap between the dynamic and static components (such as between the hub and the collar) becomes larger; The clearance between the intermediate bearing bracket and the pump barrel exceeds the standard; Inappropriate sealing ring clearance resulting in imbalance; This can occur if the gap around the sealing ring is uneven, such as the mouth ring not being grooved or the partition not being grooved. These adverse factors can cause vibration.
1.10 Factors of the pump itself
The asymmetric pressure field generated by the rotation of the impeller; Swirl in suction tank and inlet pipe; The occurrence and disappearance of vortices within the impeller, as well as in the volute and guide vanes; Vibration caused by vortex caused by valve half opening; Uneven distribution of outlet pressure due to limited number of impeller blades; Flow separation within the impeller; Surge; Pulsating pressure in the flow path; Cavitation; Water flows in the pump body, causing friction and impact on the pump body, such as water hitting the leading edge of the diaphragm and guide vane, causing vibration; The boiler feed pump transporting high-temperature water is prone to cavitation vibration; The pressure pulsation in the pump body mainly refers to the sealing ring of the pump impeller. Excessive clearance between the sealing rings of the pump body causes large leakage losses in the pump body and severe backflow, which in turn causes imbalance in the axial force of the rotor and pressure pulsation, which can enhance vibration. In addition, for hot water pumps that deliver hot water, if the preheating of the pump is uneven before startup, or the sliding pin system of the pump is not working properly, resulting in thermal expansion of the pump unit, which can 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 changes in the stiffness of the shaft support system. When the changed stiffness is an integral multiple of the system angular frequency, resonance occurs.