A liquid ring vacuum pump is simple to operate and is utilized in a number of applications across various industries. A liquid band pump works with a sealant necessary in its operation. This liquid could be water, essential oil or any other solvent which is certainly rotated by an impeller within the casing of the pump.
As the shaft turns, a liquid band is created by the centrifugal force produced by the rotating impeller. This drive holds the liquid ring against the inner wall of the pumping chamber. Because the impeller is located eccentric to the pumping chamber, the depth of access of the blades in to the liquid ring decreases and boosts as the impeller rotates. This creates increasing cell volume on the inlet slot side, creating vacuum.
On the discharge interface side, the impeller cell volume decreases as the blades move further in to the liquid band. This increases the pressure until discharge occurs through the discharge port.
A continuing flow of new sealing liquid is supplied to the pump via the Liquid-Ring Vacuum Pump sealing-liquid inlet.
Regarding the two-stage liquid ring pump, the discharge from the 1st stage does not discharge to atmosphere. 
Instead, the 1st stage discharges through the manifold resulting in the second stage as well as through a discharge slot located in the intermediate plate between the first- and second-stage impellers.