Cavitation in water pumps and its causes

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1. Cavitation: At a certain temperature, when the pressure of a liquid is reduced to its vaporization pressure at that temperature, bubbles form in the liquid. This phenomenon of bubble formation is called cavitation. 2. Cavitation collapse: The bubbles formed during cavitation shrink in size as they move to areas of higher pressure, resulting in their collapse. This phenomenon of bubbles disappearing in the liquid due to rising pressure is called cavitation collapse. 3. Causes and hazards of cavitation: During operation of a pump, if the absolute pressure of the liquid being pumped drops to the vaporization pressure of that liquid at the given temperature in certain local areas of its flow path (usually somewhere slightly downstream of the inlet to the impeller blades), the liquid begins to vaporize there, generating large amounts of steam and forming bubbles. When this liquid containing many bubbles moves forward through the high-pressure areas inside the impeller, the high-pressure liquid surrounding the bubbles causes them to shrink rapidly and eventually burst. As the bubbles coalesce and burst, liquid particles fill the voids at high speeds; this creates a very strong water hammer effect. The impact stress on the metal surface can reach several hundred to several thousand atmospheres, with an impact frequency of tens of thousands of times per second. In severe cases, this can cause the wall thickness to be breached. 4. Cavitation process: The process in a water pump in which bubbles are formed and then burst, causing damage to the flowing components, is known as the cavitation process in that water pump. After cavitation occurs in a water pump, in addition to causing damage to the flow-through components, it also generates noise and vibration, leading to a decline in the pump’s performance; in severe cases, it can even interrupt the flow of liquid within the pump, preventing it from functioning properly.