Usually, a liquid ring vacuum pump is used as a rotating positive displacement vacuum pump but it can also be used as a gas compressor compressing gases to pressures above the atmospheric.

As far as function, liquid ring pumps have similarities with a rotary vane pump but differences are crucial for achieving highest reliabilities and trouble-free operation. For instance, a liquid ring vacuum pump is designed with the rotor as being the only moving component. There are no metal-to-metal contact within the pump, no valves, no sliding vanes, no need for lubrication (other than outboard mounted bearings). The water provides the sealing while acting as the compressing media within the pumping chamber.  Compression is isothermal with very little temperature rise during compression, low noise without silencers, low vibration, cool and safe operation.