Water Ring / Liquid Ring Vacuum Pumps

The liquid ring pump compresses gas by rotating a vaned impeller within and eccentric to a cylindrical casing. Liquid (it can be any suitable liquid) is fed into the pump and, by centripetal acceleration, forms a moving cylindrical ring against the inside of the casing. This liquid ring creates a series of seals in the space between the impeller vanes, which form 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, often air, is drawn into the pump via an inlet port in the end of the casing. The gas is trapped in the compression chambers formed by the impeller vanes and the liquid ring. The reduction in volume caused by the impeller rotation compresses the gas, which reports to the discharge port in the end of the casing.
Applications:
Liquid ring systems can be single or multi-stage. Typically a multi-stage 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 vacuum generated 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.
Single stage vacuum pumps typically produce vacuum to 35 torr (mm Hg), and two-stage pumps can produce vacuum to 25 torr (mm Hg), assuming air is being pumped and the ring-liquid is water at 15°C (60F) or less. Dry air and 15°C sealant water temperature is the standard performance basis which most manufacturers use for their performance curves.