Cavitation occurs when a liquid passing through a pump vaporizes. Cavitation occurs when there is low pressure or high suction. Cavitation reduces the efficiency of the pump and can increase wear and tear on the pump. "Chemical Engineering Fluid Mechanics" by Ron Darby states, "to prevent cavitation, it is necessary that the pressure at the pump suction be sufficiently high that the minimum pressure anywhere in the pump will be above vapor pressure." Preventing cavitation can be done by increasing decreasing pressure at the intake or increasing pressure at the discharge as well as reducing the sources of potential bubbles.
Things You'll Need
- Access to the pump intake and discharge / outlet pipes
- Control of the fluid levels in the fluid storage tank
Reduce the temperature of the fluid at the pump intake. This can be done by chilling the fluid in the storage tank or by adding a cooling ring to the pump intake.
Decrease the pump speed, thus reducing the fluid flow rate.
Install a larger intake pipe, reducing friction loss.
Change the pipe configuration so that the fluid has to travel over a shorter distance. "Maintenance Fundamentals" by R. Keith Mobley recommends eliminating unnecessary bends, valves, and other head losses.
Install a restriction at the discharge line.
Install a throttling valve at the discharge line.
Replace the pump with a larger one. Alternatively, add a booster pump to supplement pressure created by the existing pump.
Reducing Bubble Sources
Decrease any aeration or mixture of liquids with air prior to its encounter with the pump to reduce the gas bubbles contained within it.
Ensure that the fluid source height is high enough to allow only liquid and not air into the pump intake. This prevents bubbles from entering. If necessary, install monitoring of the fluid holding tank level to ensure control of the fluid levels to prevent it from getting too low.
Periodically check pipes and impellers for cavitation. Replace them or resurface them to keep them smooth. Rough surfaces can cause turbulence and increase the risk of cavitation.
Tips & Warnings
- If the intake pipes are corroded, the NPSHA can be increased simply by replacing the pipes with smoother pipes.
- Cavitation can only occur when Net Positive Suction Head Available (NPSHA) is less than the Net Positive Suction Head Required (NPSHR). Preventing cavitation can be done by any means that increases NPSHA or by decreases NPSHR.
- According to "Chemical Engineering Fluid Mechanics" by Ron Darby, if the maximum suction lift is negative, the pump must be located below the upstream entrance to the suction line to prevent cavitation.
- Photo Credit bubbles image by Diana Wolfraum from Fotolia.com
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