At Jee Pumps, we take pride in our dedication to quality and our expertise in rotating equipment repair. With years of combined experience, we have encountered a wide range of issues in various types of pumps. One recurring problem that we frequently address is pump vibration. Excessive vibration in pumps can lead to unplanned and costly repairs, disrupt operations, and compromise system efficiency. In this blog, we will explore the impact of pump vibration and provide valuable insights into identifying and mitigating this issue.
Why Is Pump Vibration A Concern?
Pump vibration is a red flag that something is amiss within the pump itself or in the adjacent pump system. When the vibration level exceeds acceptable limits, the critical question arises: “What is causing this excessive vibration, and how can it be resolved?” The assumption that rotor imbalance is the sole culprit is misleading, as numerous other potential causes exist. Vibration in machinery is the result of an exciting force, whether hydraulic or mechanical, interacting with structural frequencies. The larger the amplitude of the vibration, the greater the intensity of the exciting force(s) and their proximity to the resonant frequency. Problems related to resonance reactions are frequently encountered in new installations but can also occur in older systems due to changes in the overall configuration.
Major Causes Of Pump Vibration:
1. Pump Cavitation
Cavitation is a phenomenon that manifests as a distinct noise akin to gravel being tossed around within the pump. It occurs when cavities and low-density bubbles form in the fluid on the vacuum side of the pump. Cavitation can result from improper pipe design or a clogged intake. When low-pressure bubbles approach the impeller, they collapse, causing damage to the pump’s housing and rotor.
Mitigation:
- Regularly inspect and clean filters and intake strainers.
- Reference the pump’s curve using a pressure sensor or flowmeter.
- Reevaluate the pump configuration if the fluid path is not ideal.
2. Bent Shaft
Bent shaft issues can generate significant axial vibration with phase variations approaching 180°. The location of the bend on the shaft determines whether dominant instability occurs at 1X RPM (near the shaft center) or 2X RPM (near the coupling). Detecting a bent pump shaft can be achieved using dial indicators.
3. Pump Impeller Imbalance
Pumps can sometimes exhibit symptoms that might lead one to suspect misalignment, faulty bearings, or overheating issues. However, the underlying issue can often be traced back to an imbalance within the pump assembly or another related component. This imbalance can have far-reaching consequences, including generating percussive forces and increasing heat levels within the pump.
The balance scale of the impellers plays an important role in deciding the lifespan of the pump bearings. It’s worth noting that force imbalance is a more prevalent concern compared to couple disparity when the impeller is center-hung. At the pump’s working speed, the highest vibrations are typically observed in either the horizontal or vertical direction, with the peak amplitude occurring at the pump’s operating speed (1X RPM).
The hazards associated with pump impeller imbalance are multifaceted and can have damaging effects on the entire pumping system, including:
- Shaft Deflection: An imbalance in the pump impeller can lead to shaft deflection or uncontrolled resonance, resulting in distortion and potential damage to the entire system.
- Bearing Failure: Imbalance places additional stress on the bearings, increasing the risk of premature bearing failure.
- Excessive Vibration: High levels of vibration caused by impeller imbalance can cause damage to both the pump and the surrounding system.
- Mechanical Sealing or Packing Problems: Excessive vibration and forces can disrupt the functioning of mechanical seals or packing, leading to leaks and reduced efficiency.
- Seizing of the Pump: In extreme cases, impeller imbalance can lead to the seizing of the pump, rendering it inoperable.
4. Pump Flow Pulsation
When a pump operates near its shut-off head, a particular scenario unfolds. This situation is characterized by a shift in the pressure sensors located on the outflow piping of the pump. In cases where the pump employs a discharging swing check valve, there is a noticeable fluctuation in the movement of the counterweight and valve arm, indicating an unstable flow pattern. The absence of proper feed is among the leading causes of this pulsation phenomenon.
In such instances, it is crucial for the pumped medium to maintain continuous contact with the plunger’s surface as the plunger extends and the pump becomes filled. Failure to ensure this contact can result in the plunger advancing and impacting the fluid, leading to undesirable pulsations within the system. Several factors contribute to pump flow pulsation, including:
- Incorrect Spring Rates: Inadequate spring rates can contribute to pulsation issues within the pump system.
- Valve Leakage: Leaky valves can disrupt the smooth flow of fluid and exacerbate pulsation problems.
- Multiple Pumps on a Common Header: The presence of multiple pumps connected to a single header can create flow imbalances and lead to pulsations.
- Flow-Restricting Piping Designs: Piping configurations that restrict the flow of fluid can increase the likelihood of pulsations.
- Worn Packing: Deteriorated or worn-out packing materials can exacerbate flow irregularities and contribute to pulsations.
Mitigation: To mitigate this problem and maintain a stable flow, the use of a suction stabilizer is recommended. This device helps ensure that the fluid remains consistently in contact with the plunger, thereby reducing the occurrence of pump flow pulsations.
5. Re-Circulation
Re-circulation involves flow inversion and low flow at the impeller or discharge ends. It can be categorized as suction recirculation (resulting in low-pressure bursts) or discharge recirculation. Both types can lead to cavitation and significant impeller degradation.
6. Pump Bearing Issue
Pump bearing failure is a prevalent cause of pump vibration. Only 10% to 30% of ball bearings are estimated to be utilized long enough to experience normal fatigue failure. Bearings can fail due to various factors, including overload, excessive wear, corrosion, lubrication breakdown, overheating, or contamination.
Mitigation: Regularly lubricate the bearings with appropriate oil mist, specialty oils, or grease.
7. Misalignment Of The Shaft
Since some level of vibration is expected in pumps, it’s essential to have a skilled repair specialist determine whether excessive vibration is due to shaft misalignment or another issue. Detecting shaft misalignment externally is challenging, and no sensors can directly measure the force used. Misaligned pumps may exhibit symptoms such as excessive axial or radial vibration, elevated temperatures, oil leaks, loose couplings, and shaft damage.
Mitigation: Seek professional evaluation by a repair technician to assess the extent of misalignment.
Early Detection And Preventive Measures
Early detection of vibration issues is paramount to prevent unscheduled downtime and ensure the efficiency and reliability of pump systems. If you encounter any of these vibration problems or other issues with your pumps, rotating machinery, or system, promptly contact a reliable service provider. At Jee Pumps, we are well-equipped to handle all your pump repair and customization needs, ensuring your equipment’s smooth and reliable operation.
Conclusion:
Pump vibration can have detrimental effects on industrial processes and equipment. Understanding the eight primary causes of pump vibration and the appropriate mitigation measures is crucial for maintaining optimal pump performance. By actively addressing vibration issues and seeking professional assistance when needed, you can prevent costly repairs, reduce downtime, and expand the lifespan of your pump systems.
Don’t let pump vibration disrupt your operations. Take proactive steps to mitigate these issues and ensure the longevity and efficiency of your pump systems. Contact Jee Pumps, and let us help you keep your pumps running smoothly and reliably.
