What is cavitation?

Cavitation means that when the pressure on the blade surface of the storage tank is constant, for example, when the pressure at the center of the impeller is reduced to equal to the saturated vapor pressure at the current temperature of the liquid being transported, a large number of bubbles will appear in the liquid at the inlet of the impeller. These bubbles will be quickly crushed and condensed after the liquid enters the high-pressure area. The bubbles form a vacuum, causing the surrounding liquid particles to rush towards the center of the bubbles at a very high speed, causing instantaneous impact pressure, which causes the impeller part to be quickly damaged. At the same time, the pump body vibrates and makes noise, and the flow rate, lift and efficiency of the pump are significantly reduced. This phenomenon is called cavitation. Centrifugal pump works in cavitation state: ①The pump body vibrates and makes noise ； ②The pressure head and flow rate drop significantly, and in severe cases, liquid cannot be transported. ； ③Over time, under the dual effects of water hammer impact and the chemical corrosion of metal by trace amounts of dissolved oxygen in the liquid, marks and cracks appear on the surface of the blades, and they even gradually fall off like a sponge. The allowable cavitation margin of the pump is the performance of the pump. Its value is measured experimentally. It increases with the increase of flow rate (flow rate).

When the person above mentioned cavitation, I will talk about cavitation margin. When the pump is working, the liquid will produce vapor at the inlet of the impeller due to a certain vacuum pressure. The vaporized bubbles will corrode the impeller and other metal surfaces under the impact of the liquid particles, thereby destroying the impeller and other metals. At this time, the vacuum pressure is called vaporization pressure. The vaporization margin refers to the excess energy of the unit weight of the liquid at the pump suction inlet that exceeds the vaporization pressure. Units are marked in meters, using (NPSH)r. The suction lift is the necessary NPSH Δh: That is, the vacuum degree that the pump allows to suck liquid, that is, the installation height that the pump allows, in meters. 　　Suction lift = standard atmospheric pressure (10.33 meters) - NPSH - safety amount (0.5 meters). The standard atmospheric pressure energy pressure pipeline vacuum height is 10.33 meters.

Let’s talk briefly about cavitation. When the water temperature exceeds the vaporization temperature corresponding to the pressure, the water quickly forms steam bubbles on the metal surface, and then bursts quickly. The surrounding liquid particles accelerate towards the center of the bubble, causing the particles to collide with each other, generating a high local pressure. These particles, like countless small warheads, continuously hit the pipe wall, causing damage with hole characteristics, that is, vaporization corrosion. When heating synthetic water, attention should be paid to the water temperature.