Liquid-ring compressors possess a number of desirable features. They provide a fairly steady gas flow with very small pressure fluctuations, and have low noise levels and smooth running characteristics. Including ancillary equipment, they offer a favorable capacity-to-weight ratio and small footprint, which are important advantages for small compressor packages that should be lightweight and compact. Moreover, their full-load and part-load performance is reasonably good, often better than many other compressors. A back-pullout design enables maintenance of the compressors without disassembly of piping and service liquid connections.
A liquid-ring compressor is a rotating positive-displacement device that is very similar to a rotary vane compressor; it differs in having vanes that are an integral part of the rotor that churn a rotating ring of liquid to form the compression chamber seal. Both types of compressors are inherently low-friction designs, with the rotor being the only moving part. Sliding friction often is limited to the shaft seals, although other frictions might exist. Many points presented in this article actually apply to both types.
An induction motor typically powers a liquid-ring compressor. The motor rotates a vaned impeller located within a cylindrical casing to compress gas. Liquid (often water) is fed into the compressor and, by centrifugal acceleration, forms a moving cylindrical ring against the inside wall of the casing. This liquid ring creates a series of seals in the space between the impeller vanes, forming compression chambers. The eccentricity between the impeller’s axis of rotation and the casing geometric axis results in a cyclic variation of the volume enclosed by the vanes and the ring. Gas is drawn into the compressor via an inlet port in the end of the casing; the gas is trapped in the compression chambers created by the impeller vanes and the liquid ring. The reduction in volume of the gas caused by the impeller rotation compresses the gas, which exits through the discharge port in the end of the casing.
To learn more, read "Processing Equipment: Take Advantage of Liquid-Ring Compressors" from Chemical Processing.
