Whether the pump oscillates abnormally is an important goal to measure its quality. Here, Wuhan Keerfu Pump Industry Co., Ltd. will comprehensively analyze the causes of pump oscillation for you.

1. Shaft

The shaft pump is very long. Because the rigidity of the pump shaft system is insufficient, the deflection is too large, and the linearity is poor, the moving part (transmission shaft) and the stop part (sliding shaft bearing or mouth ring) conflict with each other, forming the pump oscillation.

2. Foundation and pump support

The poor contact and fixation mode between the drive frame and the foundation, and the poor ability of the foundation and the motor system to absorb, transmit and block oscillations lead to the foundation and motor oscillation overspending, the pump foundation loosens, or the elastic foundation is formed in the process of the pump unit installation, or the oil soaked blisters lead to the weakening of the foundation rigidity, thus adding the pump oscillation frequency.

3. Shaft adapter

Poor circumferential spacing of the connecting bolts of the shaft coupling, symmetry damage, the extension of the shaft coupling, the stress of the shaft coupling, the excessive taper of the shaft coupling, the poor static or dynamic balance of the shaft coupling and other reasons will cause the pump oscillation.

4. Factors of the pump itself

Asymmetric pressure field when the impeller rotates; Eddy current of suction pool and inlet pipe; Occurrence and disappearance of vortex in impeller volute and guide vane; Oscillation caused by eddy current caused by half open valve; Because the number of impeller blades is limited, the outlet pressure distribution is uneven; Flow out of the impeller; surging; Pulsating pressure in the channel; Cavitation; When water moves in the pump body, it will conflict and impact the pump body. For example, water impacts the baffle tongue and the leading edge of guide vane, causing oscillation; The boiler feed pump transporting high-temperature water is prone to cavitation oscillation; The pressure pulsation in the pump body is mainly caused by the seal ring of the pump impeller. The clearance of the seal ring in the pump body is too large, resulting in large leakage loss. The backflow in the pump body is severe, which leads to imbalance of the rotor shaft force, pressure pulsation, and will increase the oscillation.

5. Motor

The motor structure is loose, the shaft bearing positioning device is loose, the iron core silicon steel sheet is too loose, the shaft bearing is worn, and the support stiffness decreases, which will cause oscillation.

6. Pump selection and unplanned operation

Each pump has its own rated operating point. Whether the actual operating condition is consistent with the planned operating condition has an important impact on the dynamic stability of the pump. The pump operates stably under the planned working condition, but under the variable working condition, the oscillation increases due to the radial force of the impeller.

7. Shaft bearing and smoothness

If the rigidity of shaft bearing is too low, the critical speed will be reduced, causing oscillation. In addition, the poor sealing function of the shaft bearing leads to poor wear resistance, poor fixity and excessive clearance of the shaft bearing, which is also easy to cause oscillation. The wear of the thrust shaft bearing and other rolling shaft bearings will simultaneously increase the longitudinal motion oscillation and zigzag oscillation of the shaft. Improper selection of smooth oil, deterioration, excessive impurity content, and unsmooth smooth pipeline will lead to smooth failure, worsen shaft bearing conditions, and cause oscillation. Self excitation of motor sliding shaft bearing oil film will also cause oscillation.

8. Pipes and their devices and fixing

The outlet pipe support of the pump is not rigid enough, and the deformation is too large, resulting in the pipe pressing on the pump body, which damaged the alignment of the pump body and the motor. During the process of the device, the pipe race is too big, the internal stress is large when the inlet and outlet pipes are connected with the pump, the inlet and outlet pipes are loose, the constraint stiffness drops and even the constraint stiffness is invalid, the outlet flow passage is completely cracked, the debris is stuck in the impeller, and the pipe is not smooth, such as the air bag at the outlet, and the outlet valve falls or cannot be opened.

9. Harmony between parts

The concentricity of motor shaft and pump shaft is out of tolerance. A coupler shaft is used for the joint of motor and drive shaft, and the concentricity of coupler shaft is out of tolerance. The planned clearance of dynamic parts (such as impeller adapter and mouth ring) is worn larger, the clearance between the central shaft bearing seat and the pump barrel is overspent, and the clearance of the seal ring is inappropriate, leading to imbalance and uneven clearance around the seal ring. These adverse factors can cause the pump to oscillate.

10. Impeller

The quality of the impeller pump is poor, and the quality control of the impeller manufacturing process is poor. For example, if the casting quality and processing accuracy are not qualified, the liquid transported may be corrosive, and the impeller channel may be corroded, causing the impeller to be in favor. Whether the number of blades, outlet view point, wrap angle, and the radial spacing between the throat and the outlet edge of the vane pump are appropriate. The conflicts between the central impeller ring and the pump body ring, and between the interstage bushing and the diaphragm bushing of the multistage pump will gradually become mechanical conflict wear, which will increase the pump oscillation.