1. Cavitation
When the pressure of the liquid is reduced to the vaporization pressure at a certain temperature, the liquid will produce bubbles. This phenomenon of producing bubbles is called cavitation.

2. Cavitation collapse
When the bubble produced during cavitation flows to the high pressure, its volume decreases and even bursts. This phenomenon that bubbles disappear in the liquid due to pressure rise is called cavitation collapse.

3. Causes and hazards of cavitation
During the operation of the pump, if the absolute pressure of the pumped liquid decreases to the vaporization pressure of the liquid at the current temperature in the local area of the overflow part (usually somewhere later in the inlet of the impeller blade) for some reason, the liquid begins to vaporize there, producing a large amount of steam and forming bubbles. When the liquid containing a large amount of bubbles passes forward through the high-pressure area in the impeller, The high-pressure liquid around the bubble causes the bubble to shrink sharply and even burst. At the same time of bubble condensation and rupture, the liquid particles fill the holes at a high speed, which produces a strong water hammer effect at this moment, and strikes the metal surface with a high impact frequency. The impact stress can reach hundreds to thousands of atmospheres, and the impact frequency can reach tens of thousands of times per second. In severe cases, the wall thickness will be broken down.

4. Cavitation process
The cavitation process in the water pump is the process that bubbles are produced in the water pump and bubbles break, causing the flow passage components to be damaged. In addition to damaging the flow passage components, the cavitation of the water pump will also produce noise and vibration, which will lead to the decline of the performance of the pump. In serious cases, the liquid in the pump will be interrupted and cannot work normally.

What is the characteristic curve of the pump?
Generally, the curve representing the relationship between main performance parameters is called the performance curve or characteristic curve of centrifugal pump. In essence, the performance curve of centrifugal pump is the external manifestation of the movement law of liquid in the pump, which is obtained through actual measurement. Characteristic curves include: flow head curve (Q-H), flow efficiency curve (Q- η）， Flow power curve (q-n), flow NPSH curve (q- (NPSH) r), the function of performance curve is to find a set of relative head, power, efficiency and NPSH values on the curve at any flow point of the pump. This set of parameters is called the working state, which is referred to as the working condition or working point for short. The working condition at the highest efficiency point of centrifugal pump is called the best working condition point, and the best working condition point is generally the design working condition point. Generally, the rated parameters of centrifugal pumps, that is, the design operating point and the best operating point coincide or are very close. It is very important to know the performance parameters of the pump because it can not only save energy but also ensure the normal operation of the pump when operating in the practical efficiency range.