LiquidA liquid-ring pump uses positive-displacement rotation. They are commonly employed as vacuum pumps, but they can also be utilized as gas compressors. A liquid-ring pump works similarly to a rotary vane pump, except that the vanes are an inherent component of the rotor and churn a revolving ring of liquid that forms a compression-chamber seal. The rotor is the only moving portion, hence they are naturally low-friction. The shaft seals are the only places where sliding friction exists. Induction motors are commonly used to power liquid-ring pumps. Ring Pump