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Install anti-cavitation pipe and check valve
Cavitation in a liquid ring vacuum pump typically occurs when bubbles form and collapse within the impeller and distributor (or distribution plate), causing damage to their surfaces. To address this issue, atmospheric pressure can be introduced into the compression transition zone of the pump. The method involves drilling a small hole in the compression transition area of the distributor (Yt plate) and connecting it via a pipe to the atmosphere. A check valve is installed on the other end of the pipe to prevent the working fluid or gas from escaping the pump. This piping system is known as an anti-cavitation line. When bubbles rupture during compression, introducing external high-pressure gas helps fill the void created by the bubble collapse, reducing cavitation damage and minimizing noise and vibration. The installation position of the anti-cavitation valve is illustrated in Figure 2-94.
When using an atmospheric ejector with a liquid ring vacuum pump to achieve higher vacuum levels, it is beneficial for the user's production process. In such cases, the best approach is to install a liquid ring vacuum pump combined with an air ejector. Here, the liquid ring pump serves only as the driving gas source for the ejector. The ejector then uses the viscous effect of a high-speed air stream to remove gas from the system, creating a higher vacuum. After the ejector, the liquid ring vacuum pump usually operates near 100 mbar absolute pressure. Under these conditions, the ejector can operate at 60 to 13 mbar (absolute pressure). Increasing the difference between the actual operating pressure of the liquid ring pump and the saturation vapor pressure of the working fluid inside the pump chamber enhances the anti-cavitation effect.
If a higher vacuum is required, additional pumps like Roots vacuum pumps can be added in series. Using a liquid with a lower saturation vapor pressure at the same temperature can also help avoid cavitation. Different working fluids have different vapor pressures, so cavitation may occur with water at certain temperatures and vacuums but not with other liquids that have lower vapor pressures. It is ideal to choose a working fluid with properties—such as density and viscosity—that are similar to water.
In corrosive environments, if the pump operates in a cavitation zone, it has been proven that cast iron impellers have a much shorter lifespan compared to stainless steel impellers (such as 304 or 316 grades), which offer better resistance to cavitation. If both corrosion and cavitation are present, improper material selection can lead to accelerated wear and significantly reduce the pump’s service life.
Accurate pump selection is also crucial. If the selected liquid ring vacuum pump has a suction capacity greater than the gas load of the system, the actual operating point may shift toward a higher vacuum, potentially approaching a "suffocated" state. This can cause severe cavitation, leading to excessive noise and vibration. Even if the intersection of the user's required operating point and the water temperature correction curve falls within the safe zone, if the point is close to the boundary, a large vacuum margin might result in the actual operating pressure shifting into the cavitation zone once the pump starts. Therefore, precise selection of the liquid ring vacuum pump is essential to prevent cavitation damage and ensure reliable operation.