Cavitation in water ring vacuum pumps is also well known. The damage it causes to vacuum pumps is a gradual process that can lead to impeller perforation. Cavitation is a common phenomenon in hydraulic machinery, characterized by high noise levels and severe destructive effects. Why does cavitation occur in vacuum pumps?

The underlying principle is as follows: Due to the dynamic action of the liquid, when the local pressure of the moving liquid drops below the vaporization pressure at that temperature, the liquid begins to vaporize and form bubbles. These bubbles are filled with the liquid's vapor and a small amount of gas dissolved in the liquid. When the bubbles move with the liquid into an area where the static pressure exceeds the critical pressure, the vapor inside the bubbles suddenly condenses, causing the bubbles to collapse. Since the pressure inside the bubbles is always below or near the critical value, while the pressure of the surrounding liquid is relatively high, when the bubbles collapse, the surrounding liquid rushes toward the bubble center at a very high speed, creating a high-frequency water hammer effect. This generates high local stress, local temperature increases, and produces noise and vibration. This repeated process of bubble formation and collapse can cause damage to the surfaces of components in this region. Combined with the chemical and electrochemical corrosion effects of the liquid on the component materials, this ultimately results in cavitation damage characterized by a sponge-like or honeycomb-like structure.

Research has also shown that cavitation can occur even above the critical pressure. This is because when pressure decreases, dissolved air and other gases in the liquid are released, simultaneously carrying liquid vapor with them to form bubbles filled with liquid vapor and gas. These bubbles are particularly prone to forming and growing on moving component surfaces, being carried away by the liquid, and suddenly condensing and collapsing in areas of higher pressure.

The critical pressure for cavitation varies depending on the properties of the liquid, temperature, and the nature of the dissolved gases. According to pump literature, for degassed water at room temperature, the critical pressure value for bubble formation can be taken as the saturated vapor pressure corresponding to the water temperature.