Troubleshooting Excessive Vibration
Introduction
Vibration can have a significant impact on the balancing and efficiency of a pump. Before we can work on stopping pump vibrations, we must first determine what is causing the vibration. We look at the most common causes of pump vibrations and how to avoid them.
Common Reasons
- Pump Cavitation
- Bent Pump Shaft
- Pump Flow Pulsation
- Pump Impeller Imbalance
- Bearing Failures
- Shaft Misalignment
Pump Cavitation
Occurs when the pump produces an insufficient positive suction head. When the pressure of the liquid at the impeller inlet is equal to the pressure of the liquid-vapor, it causes air pockets to form and collapse. Pump cavitation can be easily spotted by the sound of these air pockets popping. It sounds similar to rocks rumbling inside the pump, or you can even hear distinct air popping sounds. Apart from this noise, pump cavitation can also be identified by a higher energy requirement for pump operation than usual. Simple tips to prevent cavitation:
- Check if the pump filters and strainers are clean
- Use a flow meter or pressure gauge to see if the pump is operating at its ideal curve
- Re-evaluate the pump design if the pump curve is not ideal
Bent Pump Shaft
The pump’s shaft is bent, which causes high axial vibrations. Generally, bent pump shafts occur near the coupling joints. How to identify a bent pump shaft? Use dial indicators.
Pump Flow Pulsation
The pump operates near the shut-off head, it’s known as pulsation. Pump flow pulsation is caused by the following factors:
- Leaking valves
- Improper spring rates
- Lack of proper feed
- Using multiple pumps on a common header
- Worn packing valves
- Piping designs that restrict the flow
How to avoid pump flow pulsation? You can overcome pulsation problems by using a suction stabilizer that helps to keep the displaced fluid in continuous contact with the plunger.
Pump Impeller Imbalance
It is an imbalance in the pump assembly, it causes vibrations and heat generation. Balancing the pump impellers extends the life of the bearings, which in turn reduces excessive vibrations. Some of the dangers of pump impeller imbalance are:
- Bearing failure
- Pump seals failure
- Excessive vibration
- Shaft deflection, which leads to bent shafts
- Pump seizures
How to avoid it? Get your pump maintenance engineer to precision align the impellers for overcoming all these issues.
Bearing Failures
The main reason for pump vibrations is bearing failure. While your pump may work for 20,000 hours without any issues, the pump bearings give out long before that. The reasons for pump bearing failure are many: corrosion, inadequate lubrication, contamination, excessive wear and tear, weather conditions, overheating, and more. Apart from these issues, another main cause of pump bearing failure is the wrong selection of bearings. How to avoid it? You can overcome pump bearing issues by lubricating bearings regularly with pump manufacturer-recommended oils. Also, replace bearings regularly to avoid excessive vibrations.
Shaft Misalignment
Impeller imbalance, shaft misalignment can cause excessive vibrations. Shaft misalignments cannot be detected externally and require professional intervention. If vibrations continue, even after rectifying the above conditions, it may be because of shaft misalignment. Here are a few signs that indicate there is shaft misalignment in your pump:
- Excessive oil leaks along with the bearing seals
- Coupling failures
- Loose foundation bolts or coupling
- High oil discharges
- Heat generation near the bearings and casings
- Excessive radial or axial vibration