Propellers, impellers, and pumps are important parts of daily infrastructures. They keep boats, production facilities, and power plants running worldwide.
However, one major concern for engineers designing and using them is to prevent cavitation. To prevent that, engineers must make sure they install the right equipment in the system.
What Cavitation Is
Pumps are often made to pump liquids, but when combined pressure and flow rate aren’t conducive to the liquid being pumped, cavities or pockets form, leading to cavitation.
Some people describe cavitation of pumps as the collapse and creation of air bubbles in fluids. Although they might look like air, technically, the bubbles are a vacuum, gaseous vapor, or cavity.
Although cavitation is possible in all pumping supplies, it is very common in centrifugal pumps, where bubbles develop quickly around the axis of the impeller. When bubbles pass through the center of impellers to the outer edges, centrifugal force creates a high pressure that causes bubbles to implode or collapse with a greater force.
There are different kinds of cavitation. It is imperative to understand all of them so that you can look for an effective way to prevent cavitation from taking place.
These types of cavitation may include the following:
- Air aspiration – Air may sometimes be sucked in a pump via failing valves and other weak points, like joint rings. Once air is inside, it has nowhere to go. As the liquid gets swished around, it forms bubbles that pop-under pressure from an impeller.
- Internal re-circulation – In this case, pumps are unable to discharge at the right rate. So, that means the liquid gets re-circulated around an impeller. Usually, the liquid flows through high and low-pressure zones, leading to high velocity and heat.
- Vane syndrome – In this type, cavitation happens when an impeller has a large diameter, or the housing has a thick coating. Both of these create little space in the housing itself.
- Turbulence – If the system’s parts, including elbows, filters, valves, and pipes, are inadequate for the type or amount of liquid, it creates vortexes. This makes liquid turbulent and experiences pressure differences.
- Vaporization – It happens when centrifugal pumps impart velocity on liquids as they pass through the impeller’s eye. If an impeller isn’t working well, some liquid can quickly be vaporized or boiled, creating a tiny shock wave.
Cavitation often results from the subsequent collapse and formation of vaporized bubbles in the pumped liquid. One of the most common causes of cavitation is the poor condition of the pump inlet. Disruptions to flow can have a few causes, from component degradation to system designs. This flow disruption can be caused by excessively long inlet piping, poorly specific pumps, and collapsed or restricted inlet hoses.
Apart from poor pump inlet condition, other causes of cavitation are:
- Pressure dropping in the suction nozzle
- Temperature increase
- Fluid velocity increase
- Choosing pumps incorrectly
The Bottom Line
By avoiding cavitation, you significantly increase the lifespan and efficiency of your pumps. So, always watch the impeller closely for signs of corrosion and pitting; also, listen to your pumps to ensure there is no sound, like marble banging.