Liquid Ring Pump

A liquid-ring pump is a rotating positive-displacement pump and is typically used as a vacuum pump, but can also be used as a gas compressor. The function of a liquid-ring pump is similar to a rotary vane pump, with the difference being that the vanes are an integral part of the rotor and churn a rotating ring of liquid to form the compression-chamber seal. They are an inherently low-friction design, with the rotor being the only moving part. Sliding friction is limited to the shaft seals. Liquid-ring pumps are typically powered by an induction motor

The earliest liquid-ring pumps date from 1903, when a patent was granted in Germany to Siemens-Schuckert. US Patent 1,091,529, for liquid-ring vacuum pumps and compressors, was granted to Lewis H. Nash in 1914. They were manufactured by the Nash Engineering Company in Norwalk, CT. Around the same time, in Austria, Patent 69274 was granted to Siemens-Schuckertwerke for a similar liquid-ring vacuum pump

Liquid-ring systems can be single- or multistage. Typically a multistage pump will have up to two compression stages on a common shaft. In vacuum service, the attainable pressure reduction is limited by the vapour pressure of the ring-liquid. As the generated vacuum approaches the vapour pressure of the ring-liquid, the increasing volume of vapor released from the ring-liquid diminishes the remaining vacuum capacity. The efficiency of the system declines as a result