The liquid ring pump is mainly used for vacuum pumping and conveying the gas medium, its working principle as shown in figure 2-14. The impeller is eccentrically straight blade configuration in the cylinder, and the introduction of a certain amount of liquid in the cylinder, usually with water.

   Wheel rotation and reaches a certain speed, due to the centrifugal force, the liquid thrown around, to form a paste in the liquid ring surface of the cylinder body. The upper part of the liquid ring and the inner surface of the wheel hub tangent, a crescent shaped space is formed between the impeller and the liquid ring, the space is divided into a number of different work wheel blades volume chamber (the element volume). Wheel rotates, the element volume right semi circle gradually expanded, the element volume left half, gradually narrowing. Accordingly the sickle shaped arranged at both sides of the cylinder end cap on the suction and exhaust port. On the right side of the scythe hole for the suction inlet, the outlet hole for a small sickle. Thus, wheel rotation, each element volume expansion, reduce the time, and with inlet and outlet connected - time, achieve suction, compression, exhaust and possible expansion process. Therefore, the liquid ring pump is a volume type compressor.

As the gas discharge, but also with a portion of the liquid discharge, so must be added a certain amount on the suction liquid, the liquid environment with constant volume, and to take away the heat, cooling effect. The liquid ring pump work, blade stirring a liquid to generate energy loss big, known as the hydraulic loss, loss of energy is almost equal to the compressed air consumption. Therefore, the liquid ring pump efficiency is very low, isothermal efficiency is only 0.30-0.45, a large machine can reach 0.48-0.52. Because of general vacuum pump power consumption is small, so the liquid ring pump is often used as vacuum pumps. In order to avoid the hydraulic loss is too large, the general working round the outer end of the maximum circumference speed limit is 14 ~ 16m/s, and as far as possible the selection of low viscosity liquid as liquid ring. In order to further reduce the hydraulic loss, can also be used with rotatable structure.

The liquid ring pump is usually water as sealing liquid, are mostly used as vacuum pump, so it used as water ring vacuum pump. Due to the full role of cooling liquid, the compression process is close to the isothermal compression, compression of the gas temperature is very low, no friction between the metal surface of the pump, the medium is not in direct contact with the cylinder, so suitable for gas conveying flammable, explosive, high temperature decomposition and has a strong corrosive. The machine has the advantages of simple structure, does not need the suction and exhaust valve, steady work, reliable, uniform gas; drawback is that efficiency is too low.