What is cavitation, and what is the cavitation margin?

One more question: on which pumps does this phenomenon occur?

Water boils at 100 degrees at one atmosphere of pressure, but in Tibet it boils at a temperature lower than 100 degrees. Cavitation is the process in which a liquid vaporizes to form bubbles, which are then crushed. NPSH is the head of pressure available over the medium to be vaporized, with the common unit being meters. The net positive suction head available for the device is akin to water at 100 degrees Celsius under normal pressure, with a liquid level height of 4 meters; thus, there is a net positive suction head of 4 meters at the lowest point of the liquid level (without taking into account pipeline losses). Centrifugal pumps also have a NPSH margin, known as the required NPSHr of the pump. If the pump’s NPSHr is 4 m, in such a situation, vaporization will occur as the liquid enters the pump, and the pump will become unusable. It is generally required that NPSHa be at least 0.6 m greater than NPSHr.

Cavitation occurs when the fluid being transported vaporizes, forming bubbles. When there are enough of these small bubbles, they burst, releasing a large amount of energy that damages the components involved in the flow, especially the impeller; as a result, the pump exhibits vibration, noise, and abnormal sounds； NPSH is the head of energy required to prevent the medium being transported from vaporizing as it enters the pump; in other words, it refers to a height value. It can be divided into the NPSH required for plants in chemical factories and the NPSH necessary for pumps, as explained clearly by the moderator. In the case of backflow, the higher the installation height of the device above the water pump inlet, the less likely cavitation will occur. Of course, this also depends on factors such as the local atmospheric pressure of the medium, its vaporization pressure, temperature, and pipe losses ； The suction principle is more or less the same

Why does cavitation occur, and does it mean the pump can no longer be used?

The pumped gas creates a very weak centrifugal force, which is not sufficient to draw liquid continuously into the pump; therefore, it cannot be used

Cavitation is a phenomenon, and the cavitation margin is a value :lol

NPSH can be divided into two types: the NPSHa, which refers to the liquid level height in the system, and the NPSHr, which represents the value that must be met by the working medium in order for the pump to function properly during operation. Under normal circumstances, an insufficient r value can be improved by adding an inducer wheel or increasing the inlet pressure. Cavitation refers to the phenomenon that occurs when there is insufficient cavitation margin; its occurrence can lead to damage to the impeller, and in severe cases, it may even cause the pump to burn out.

Cavitation occurs at the inlet of the impeller (where vaporization is most likely to take place), where bubbles are formed and then burst. Microscopically, the impact force on the impeller is very large, which can easily cause damage to the impeller ； Additionally, the generation of gas prevents the liquid from being drawn up continuously, causing the impeller to transport both gas and liquid together, which leads to abnormal vibrations and even equipment damage.

May I ask, is this 0.6 meter a safety margin in certain formulas? For example, this one. 🔺h=10.33-npshr-safety margin