1. Main causes of pump vibration
1. Cavitation or insufficient inlet conditions
Cavitation may occur in the pump when the inlet pressure is too low, the suction pipeline is blocked, the liquid level drops, the medium temperature rises, or the pipeline resistance is too large. The bubbles burst in the high-pressure area of the impeller, which will produce irregular noise, broadband vibration, and cause pitting corrosion of the impeller.
Confirm when selecting:
NPSHa > NPSHr + Safety Margin
High temperature, volatile media and long-distance suction systems require more sufficient cavitation margin. During processing, the inlet valve, filter pressure difference, liquid level, medium temperature and suction pipe diameter should be checked instead of simply reducing the vibration alarm value.
2. Poor coupling alignment
Parallel or angular deviation between the pump shaft and the motor shaft will produce obvious axial and radial vibration, and increase the load on the coupling and bearings. After the equipment is running hot, pipe stress and thermal expansion may also change the cold alignment results.
3. Rotor imbalance or shaft bending
Impeller fouling, corrosion and wear, manufacturing deviations, foreign matter attachment or shaft bending will all cause unbalanced rotating mass. A more obvious rotational frequency component can usually be observed in the spectrum, that is, 1× operating speed frequency.
4. Operation deviating from the optimal efficiency point
If the pump operates in an area of too small or too large flow for a long time, internal backflow, increased radial force, increased noise and decreased efficiency may occur. The best efficiency point (BEP) is the operating point at which the pump has the highest efficiency. The actual selection should make the rated operating conditions as close as possible to the manufacturer's recommended operating range.
5. Bearing, foundation or pipeline problems
Insufficient bearing lubrication, excessive grease, contamination, abnormal clearance or fatigue damage will cause high-frequency vibration and temperature rise. Insufficient base stiffness, hollow grouting, loose foundations and structural resonance may amplify the original vibration.
2. What parameters need to be checked to diagnose pump vibration?
| Inspection items | Diagnosis function |
|---|---|
| Vibration speed mm/s RMS | Evaluate the overall vibration intensity of the equipment |
| Vibration displacement μm | Judge low-frequency vibration and shaft system swing |
| Vibration acceleration m/s² or g | Identify bearings and high-frequency impact |
| Axis, horizontal, vertical direction | Distinguish between alignment, foundation and hydraulic problems |
| 1×, 2× frequency conversion in the spectrum | Assist in judging imbalance and misalignment |
| Flow, head, inlet Pressure | Judge whether it deviates from the design conditions |
| Bearing temperature and motor current | Judge friction, overload or lubrication abnormality |
Whether the vibration is qualified cannot be judged by just one general value. It should be combined with the pump type, power, speed, basic form, measurement location and the ISO adopted by the project. 20816, API 610 or manufacturer acceptance criteria.
3. How should the scene be investigated and handled?
Firstly, record the vibration in three directions of the driving end and non-driving end bearing positions under stable working conditions, and simultaneously record the flow, pressure, rotation speed, current and temperature. Then check in the following order:
Check the inlet liquid level, valves, filters and signs of cavitation;
Confirm whether the actual working point is within the recommended operating range;
Check the feet, Base, grouting and pipe supports;
Measure coupling alignment and soft feet;
Check bearing lubrication, clearance and damage;
Check impeller blockage, wear, balance and pump shaft runout.
If the vibration suddenly rises sharply and is accompanied by the sound of metal friction, a rapid increase in temperature, or a violent fluctuation in flow, the machine should be shut down for inspection in time to avoid further damage to the bearings, mechanical seals and rotors.
4. How to reduce the risk of vibration during procurement?
Purchasers should not only provide flow rate and head, but also describe the medium composition, temperature, density, viscosity, solid content, inlet pressure, NPSHa, operating mode, adjustment range, installation environment and applicable standards.
For high-temperature molten salts, chemical corrosive media, solid particles or continuous operating conditions, key confirmations should also be made:
Whether the pump type and impeller structure are suitable for the medium;
The relationship between rated operating conditions and BEP;
Bearings, shafting and Base stiffness;
Dynamic balance level and factory vibration test;
Thermal expansion, pipeline load and sealing scheme;
Whether performance curves and inspection documents are provided.
5. Feiyue Pump Industry’s product solutions
For petrochemical, high-temperature molten salt, chemical process and harsh industrial transportation conditions, Jiangsu Feiyue Pump Industry can select pump types based on medium properties, system curves and on-site installation conditions, and provide performance curves, material configurations, shafting design and factory inspection support.
Providing complete working conditions before purchasing can help arrange the rated working point of the pump in a reasonable operating area, reduce the risk of cavitation, radial load and abnormal vibration from the design stage, and improve the continuous operation reliability of the pump unit.
