Common Causes of Slurry Pump Vibration

According to relevant statistics, abnormal vibration in slurry pumps is a primary cause of other failures. Simultaneously, equipment malfunctions directly intensify pump vibration, creating a vicious cycle that severely impacts the safe operation of the equipment. This leads to increased maintenance costs and production losses due to equipment downtime.

I . Analysis of Slurry Pump Vibration Causes

1. Impeller Mass Unbalance Fault
The centrifugal force generated by an impeller mass imbalance constantly acts on the slurry pump. During manufacturing, components undergo inspection and adjustment, with the impeller specifically subjected to static/dynamic balancing tests and drilling/milling for correction. Areas of imbalance are machined, resulting in a relatively optimal state of mass balance. Consequently, the pump operates most stably with minimal vibration. However, after prolonged operation, factors like impeller wear and scaling from slurry adhesion disrupt the overall mass balance, leading to an uneven load or "eccentric loading" on the impeller. The heavier side of this imbalanced impeller experiences increased centrifugal force, especially at high rotational speeds, causing significant unbalanced rotational forces. Measurements typically show vibration amplitude increasing progressively from the motor end towards the pump end.

2. Vibration Fault Induced by Coupling
Coupling-induced vibration is relatively common in slurry pumps, particularly with rigid couplings. Vibration from both the motor and pump can resonate through the coupling, amplifying overall vibration. Even for commonly used pin-type flexible couplings, failure of pins/rubber rings to accommodate axial movement can cause intense, brief vibration. While coupling faults contribute to pump vibration, they are generally less severe than those caused by impeller issues. Couplings also undergo balancing alignment after manufacturing.

Coupling alignment, like impeller balancing, aims to minimize unbalanced forces during rotation. However, besides its own mass balance, coupling installation must satisfy two conditions for paired alignment:

1. Coincidence of the two coupling hubs, meaning their outer circumferences align.

2. Parallelism of the coupling mating faces (end faces), ensuring the two centerlines are parallel.
   Only when these conditions are met can stable equipment operation and minimal coupling component wear be better ensured.

3. Vibration Caused by Loose Fastening Bolts
Even well-operating equipment experiences "micro-vibrations." Over time, these cause bolts at the pump casing, bearing housing, and baseplate to loosen. Loose bolts allow the pump casing to move more freely, increasing vibration. If not promptly tightened, this increased vibration further loosens and wears the bolts, creating a vicious cycle that ultimately leads to more significant pump failures.

4. Faults Due to Bearing Wear or Insufficient Lubrication
Bearing service life is directly related to the operating environment and lubrication. Lubricant leakage is a very common issue in slurry pumps. Oil seals on both sides of the bearing housing may fail, leading to persistent seepage. Alternatively, blocked oil passages due to contaminated lubricant can impair bearing lubrication. Insufficient lubrication, regardless of existing bearing wear, causes noise and vibration. This occurs because the lack of an oil film leads to direct metal-to-metal contact between rolling elements, eliminating damping capability. Although initially slight, this vibration is highly detrimental. Furthermore, many slurry pump bearing housings use labyrinth seals, which prevent oil leakage but do not fully block external contaminants from entering the bearings, potentially causing wear from contamination.

5. Equipment Faults Caused by Unstable Feed Conditions
Slurry pumps often operate under harsh conditions, with many handling high flow rates. During slurry transport, large debris can interfere with or even block the impeller channels, disrupting feed. Unstable or insufficient feed causes severe cavitation within the pump volute. This disrupts the impeller's hydraulic balance, not only generating vibration but also posing a serious threat to equipment safety.

II. Hazards of Slurry Pump Vibration

1. Impact on Service Life of Pump Components
Statistics indicate that vibration-related faults account for approximately 74% of slurry pump failures. During operation, imbalance increases centrifugal loads on bearings. Vibration exceeding allowable limits prematurely breaks down the lubricant film on bearing rolling surfaces. Inadequate lubrication and heat dissipation lead to elevated bearing temperatures, accelerating failure.

2. Mechanical Seal Damage and Leakage
While vibration's impact on mechanical seals is less pronounced than on bearings, it remains a major cause of seal failure. Vibration prevents stable contact between the seal faces, potentially causing initial minor slurry leakage. Since slurry pumps often use double mechanical seals, vibration can also allow slurry particles to enter between the friction faces during operation, leading to premature seal face damage. Additionally, vibration can cause premature fatigue failure of the compression spring and excessive wear of O-rings, resulting in leakage.

3. Pump Casing Wear and Leakage
To enhance centrifugal pump efficiency, clearances between internal components like the impeller, front/rear wear plates, and volute are minimized during design (smaller gaps generally yield higher efficiency under similar conditions). Vibration causes axial shaft movement and runout, which is highly damaging to internal components. It can also lead to impact or wear between wear plates and the impeller. Such damage compromises pump performance or reduces efficiency. Friction forces on internal components due to vibration can also cause leakage at joint faces.

4. Increased Energy Consumption per Unit Device
Vibration in slurry pumps creates additional frictional losses and uneven centrifugal forces. This not only reduces operational stability but also lowers pump efficiency, increasing wasted energy for the same output and leading to higher power consumption.

5. Occurrence of Shaft Breakage
The pump shaft transmits rotation and maintains the impeller's stable position. Vibration-induced unbalanced centrifugal forces on the impeller subject the shaft to excessive stress. Long-term operation under such conditions leads to metal fatigue and ultimately shaft fracture.

III. Prevention and Treatment of Pump Vibration

Pump vibration cannot be eliminated entirely but can be mitigated through effective measures. For long-term stable operation of slurry pumps, proper selection and standardized operation are crucial. Vibration is a double-edged sword: it can cause severe faults, but monitoring vibration changes also allows timely detection and diagnosis of emerging problems.

(1) Selection: Slurry pump operating conditions and environments are typically harsh, leading to relatively high failure rates. Therefore, selecting equipment with higher specifications (within technical requirements) is advisable, alongside ensuring favorable feed conditions.

(2) Operation: Centrifugal pumps experience some cavitation during operation, which worsens with insufficient feed, increasing vibration. Short-term vibration from cavitation is caused by uneven liquid distribution in the volute. Stabilizing the feed or adjusting the outlet valve/pump speed can effectively reduce vibration. However, prolonged cavitation causes uneven impeller wear, leading to unadjustable vibration.

(3) Lubrication: Lubrication involves not only oil level and quantity but also viscosity. Insufficient lubricant viscosity can cause vibration. Bearing housing temperature rises during operation, lowering oil viscosity. Therefore, while checking oil levels, ensure operating temperature remains within an appropriate range. Investigate causes of temperature rise promptly, as overheating also leads to bearing vibration and damage from poor lubrication.

(4) Tightening: Bolts can loosen under "micro-vibration." Applying thread-locking compound during reassembly after maintenance can prevent loosening and thread damage. The compound can be melted with heat for disassembly. This small investment is essential for equipment reassembly.

(5) Stabilizing Feed: Feed stability relates to selection and installation. However, during operation, sedimentation, scaling, or large particle blockages in pipelines can restrict flow below pump requirements, necessitating line and valve cleaning. For flow control, reducing pump speed (frequency) is preferred, followed by adjusting the outlet valve. Adjusting the inlet valve for flow control is not recommended.

IV. Conclusion

Equipment failures often begin with subtle abnormal vibration that progressively intensifies. This process offers many aspects for summary and analysis. Abnormal vibration is both a fault symptom and a significant contributor to fault escalation. Analyzing abnormal vibration serves as a diagnostic tool. Failure to address equipment issues promptly based on vibration trends creates a vicious cycle: more severe vibration indicates higher likelihood of faults, and existing faults, in turn, worsen vibration.