A liquid ring vacuum pump has an impeller with blades mounted on a center hub positioned in a cylindrical body but off-set from the guts.
In Body 1 to the right, you can observe the blades close to the the 
surface of the pump are closer to the exterior wall than at the sides and bottom level of the pump. You can view this more obviously in Figure 2.
The impeller sits among two end Roots Vacuum Pump plates (port plates) that have shaped holes cut into them called ports.
The pump requires a liquid (also known as the sealant) to create vacuum as follows. Prior to starting the pump, it must be partially filled up with the liquid sealant. The liquid can be water (rendering it a water band pump), oil or a solvent, depending upon the application.