A liquid band vacuum pump is easy to operate and is utilized in several applications across various industries. A liquid ring pump works with a sealant needed in its operation. This liquid could be water, oil or any various other solvent which is certainly rotated by an impeller Liquid-Ring Vacuum Pump within the 
casing of the pump.
As the shaft turns, a liquid band is created by the centrifugal force generated by the rotating impeller. This pressure holds the liquid band against the inner wall structure of the pumping chamber. Since the impeller is located eccentric to the pumping chamber, the depth of entry of the blades in to the liquid ring reduces and raises as the impeller rotates. This creates increasing cellular volume on the inlet interface side, creating vacuum.
On the discharge interface side, the impeller cell volume decreases as the blades move further into the liquid band. This escalates the pressure until discharge occurs through the discharge slot.
A continuous flow of fresh sealing liquid is supplied to the pump via the sealing-liquid inlet.
Regarding the two-stage liquid ring pump, the discharge from the first stage does not discharge to atmosphere. Rather, the 1st stage discharges through the manifold leading to the second stage in addition to through a discharge port located in the intermediate plate between your first- and second-stage impellers.