A positive displacement compressor consisting of a vaned impeller positioned eccentrically inside a cylindrical casing. A working liquid, usually water, inside the casing forms a moving cylindrical ring against the inside of the casing. This liquid ring creates a series of spaces between the impeller vanes, which forms multiple compression chambers. The eccentricity between the impeller’s axis of rotation and the casing geometric axis results in a gradual volumetric reduction, or compression, between the vanes and the ring as gas moves from the suction to the discharge end of the compressor. The compressed gas exiting the discharge nozzle contains a certain amount of working liquid usually removed in a vapor–liquid separator. Liquid ring compressors are often used as vacuum pumps but can also be used as a gas compressor.