Water ring vacuum pump (referred to as water ring pump) is a kind of rough vacuum pump, the ultimate vacuum it can obtain is 2000~4000Pa, and the series atmospheric ejector can reach 270~670Pa. The water ring pump can also be used as a compressor, which is called a water ring compressor, which is a low-pressure compressor with a pressure range of 1~2×105Pa gauge pressure.

The water ring pump was originally used as a self-priming pump, and then gradually used in many industrial sectors such as petroleum, chemical industry, machinery, mining, light industry, medicine and food. In many processes of industrial production, such as vacuum filtration, vacuum water diversion, vacuum feeding, vacuum evaporation, vacuum concentration, vacuum resuspension and vacuum degassing, water ring pumps are widely used. Due to the rapid development of vacuum application technology, the water ring pump has always been paid attention to in obtaining rough vacuum. Since the gas compression in the water ring pump is isothermal, it can pump out flammable and explosive gases, and also pump out dusty and water-containing gases. Therefore, the application of water ring pumps is increasing.
As shown in the picture: the pump body is filled with an appropriate amount of water as the working fluid. When the impeller rotates clockwise as shown in the figure, the 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 cavity. The inner surface of the lower part of the water ring is just tangent to the impeller hub, and the upper inner surface of the water ring is just in contact with the tip of the blade (in fact, the blade has a certain insertion depth in the water ring). At this time, a crescent-shaped space is formed between the impeller hub and the water ring, and this space is divided into several small cavities equal to the number of blades by the impeller. If the bottom 0° of the impeller is taken as the starting point, the volume of the small cavity changes from small to large when the impeller rotates 180 degrees before, and it communicates with the suction port on the end face. At this time, the gas is inhaled, and when the suction ends, the small cavity It is isolated from the suction port; when the impeller continues to rotate, the small cavity becomes smaller, so that the gas is compressed; when the small cavity is communicated with the exhaust port, the gas is discharged out of the pump.

In summary, the water ring pump relies on the change of the pump chamber volume to achieve suction, compression and exhaust, so it is a variable volume vacuum pump.

Compared with other types of mechanical vacuum pumps, the water ring pump has the following advantages
The structure is simple, the manufacturing precision is not high, and it is easy to process.
The structure is compact, and the number of revolutions of the pump is high. Generally, it can be directly connected with the motor, without the need for a deceleration device. Therefore, with a small structure size, a large exhaust volume can be obtained, and the floor space is also small.
Compressed gas is basically isothermal, that is, the temperature of the compressed gas changes very little.
Since there is no metal friction surface in the pump cavity, there is no need to lubricate the pump, and the wear is very small. The sealing between the rotating part and the fixed part can be done directly by the water seal.
The suction is uniform, the work is stable and reliable, the operation is simple, and the maintenance is convenient.
The water ring pump also has its disadvantages
Low efficiency, generally around 30%, better up to 50%.
The low degree of vacuum is not only limited by the structure, but more importantly by the saturated vapor pressure of the working fluid. Using water as working fluid, the ultimate pressure can only reach 2000~4000Pa. Use oil as working fluid, up to 130Pa.

In short, because the gas compression in the water ring pump is isothermal, it can pump out flammable and explosive gases. Since there is no exhaust valve and friction surface, it can pump out dusty gas, condensable gas and gas-water mixture. With these outstanding features, despite its low efficiency, it is still widely used.