Cavitation is an undesirable and harmful phenomenon, but unfortunately often ignored. It should be prevented because it can lead to, among others: to erosion of pump components, and in extreme cases to irreversible damage.
What is the cavitation phenomenon?
Cavitation is a process involving the formation, accumulation and sudden disappearance of gas bubbles in the liquid around the pump impeller. The phenomenon is accompanied by sudden changes in pressure.
Cavitation occurs when the liquid pressure drops in the central part of the impeller, which in turn results in liquid inflow through the suction port.. When the pressure drops below the saturation level at room temperature, the liquid begins to evaporate. This is when small bubbles are created, which break up, creating a shock wave with quite high energy. Cracks of large numbers of bubbles cause micro-impacts that contribute to the development of corrosion of construction materials and serious damage.
What are the main symptoms of cavitation in a pump?
submersible pump, which is subject to the phenomenon of cavitation, may produce certain characteristic symptoms. First of all, there is a clear decrease in its operating parameters and efficiency. There is also an increased consumption of electricity. The pump is noisy and vibrates due to pressure pulsation. After disassembly, visible damage to structural elements caused by corrosion can be noticed, especially the rotor. This damage during operation may cause leaks.
How to counteract cavitation?
The better the anti-cavitation properties of the pump, the higher the level of cavitation resistance. Therefore, the basis may be to counteract this phenomenon structurally, including: appropriate design of rotors, proper blade profiling, use of a limited number of blades or pre-rotation (pre-swirl in the direction of engine rotation). These types of activities are undertaken by device manufacturers, and the consumer's role is to select a high-quality pump that has all these features. This property is referred to as the NPSHA parameter.
The NPSHA parameter can be increased in several ways. One of them is the use of a pipeline of short length and large diameter in the installation. It is also necessary to plan the installation with as few elements as possible contributing to pressure losses. It is also necessary to prevent liquid velocities above 2 m/s and fluctuations in the pump's suction pressure. Liquids should be pumped at the lowest possible temperature. It may also be helpful to use a pipeline with a smooth internal surface (e.g. PVC).
