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 center.
In Number 1 to the proper, you can see the blades close to the top of the pump are nearer to the outside wall than at the sides and bottom level of the pump. 
You can see this more clearly in gear box for greenhouse Figure 2.
The impeller sits between two end 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. Before you start the pump, it must be partially filled up with the liquid sealant. The liquid could be water (making it a water ring pump), essential oil or a solvent, dependant on the application.