What is cavitation in centrifugal pumps ?
The formation and bursting of vapour bubbles in a centrifugal pump due to change in pressure is called cavitation. This hydrodynamic phenomena have a significant impact on the overall performance of the pump. When sudden reduction in pressure occurs, liquids that have temperatures close to their boiling points often undergo this formation of bubbles.
How does it affect the pump?
- Cavitation is actually responsible for the degradation of the pump which in turn results in fluctuations of the flow rate and pressure at discharge.
- Material damage: It can also damage the internal components of the pump.
- The bubbles cause a physical shock on the edge of the impeller vane which creates small pits extremely minute in size. However the cumulative effect of these pits formed over time can destroy the impeller.
- Cavitation in centrifugal pumps could also cause excessive vibration in the pump. Vibrations can damage rings, seals and pump bearings.
How to identify if a pump is cavitating ?
One of the major indicators of cavitation in centrifugal pumps is the noise. The pump will sound like shaking can full of marbles. Other indications include:
- Fluctuation in discharge pressure,
- Fluctuations in flow rate,
- Distinctive crackling noise,
- Fluctuations pump motor current,
- Erratic power consumptions,
- Reduction in pump efficiency and output
How can you avoid cavitation in centrifugal pumps?
As cavitation happens on the suction side of the pump, all preventive measures must be directed towards this area. If the suction lift is too high, it is definitely going to cause cavitation. Hence, centrifugal pumps must be less than 4 meters above the water level to avoid this problem. Some of the other guidelines that you must follow are:
- Minimize the number of bends in the suction line
- Rather than using concentric reducers, make use of eccentric ones
- Also, make sure that the straight side of this reducer is properly fitted above the suction line
- The length of the suction must be minimal
- Use the less number of valves in the suction line
- Increase the size of the valves
- Suction pipe and pump inlet connection must be of the same diameter
- Suction pipe must be airtight
Manufacturers like Rotech Pumps design centrifugal pumps that can operate under conditions wherein cavitation is unavoidable. They design special centrifugal pumps that can withstand small amounts of cavitation occurring during their operation. Rotech Pumps continuously strives to make improvements in design and engineering of pumps, pump parts and mechanical seals. They are renowned internationally for their wide range of quality pumping products and accessories. You can log on to their website rotechpumps.com for further details.