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 Number 
1 to the proper, you can view the blades near the the surface of the pump are closer to the outside wall than at the sides and bottom of the pump. You can observe this more Gear box clearly in Figure 2.
The impeller sits among two end plates (port plates) which have shaped holes cut into them called ports.
The pump requires a liquid (also called the sealant) to create vacuum the following. Prior to starting the pump, it should be partially filled with the liquid sealant. The liquid could be water (making it a water ring pump), oil or a solvent, depending upon the application.