Circulating water vacuum pump, also known as water ring vacuum pump, is a type of rough vacuum pump. The maximum vacuum it can achieve is 2000-4000 Pa, and the series atmospheric injector can reach 270-670 Pa. Water ring pumps can also be used as compressors, known as water ring compressors, which are low-pressure compressors with a pressure range of 1-2X105 Pa gauge pressure.

The circulating water vacuum pump was initially used as a self-priming pump, and later gradually applied to many industrial sectors such as petroleum, chemical, machinery, mining, light industry, medicine, and food. In many industrial production processes, such as vacuum filtration, vacuum water intake, vacuum feeding, vacuum evaporation, vacuum concentration, vacuum moisture regain, and vacuum degassing, water ring pumps are widely used. Due to the rapid development of vacuum application technology, water ring pumps have always been highly valued for obtaining rough vacuum. Due to the isothermal compression of gas in water ring pumps, flammable and explosive gases can be extracted, as well as gases containing dust and water. Therefore, the application of water ring pumps is increasing as the pump body contains an appropriate amount of water as the working fluid. When the impeller rotates clockwise as shown in the figure, water is thrown around by the impeller. Due to the centrifugal force, the water forms a closed ring of approximately equal thickness determined by the shape of the pump chamber. The inner surface of the lower part of the water ring is exactly tangent to the impeller hub, and the inner surface of the upper part of the water ring is exactly at the top of the blade (in fact, the blade has a certain insertion depth inside the water ring). At this point, a crescent shaped space is formed between the impeller hub and the water ring, and this space is further divided into several small chambers equal to the number of blades by the impeller. If the lower zero of the impeller is taken as the starting point, then when the impeller rotates 180 degrees before, the small chamber area increases from small to large and is connected to the suction port on the end face. At this time, gas is sucked in, and when the suction is completed, the small chamber is isolated from the suction port; When the impeller continues to rotate, the small chamber becomes smaller, compressing the gas; When the small chamber is connected to the exhaust port, the gas is discharged outside the pump.

In summary, the circulating water vacuum pump relies on changes in the pump chamber volume to achieve suction, compression, and exhaust, making it a variable capacity vacuum pump.