A liquid band vacuum pump has an impeller with blades mounted on a center hub located in a cylindrical body but off-set from the guts.
In Shape 1 to the proper, you can view the blades close to the the surface of the pump are nearer to the outside wall than at the sides and bottom level of the pump. You can view this more obviously in 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 called the sealant) to create vacuum the following. Prior to starting the pump, it must be partially Water Ring Vacuum Pump filled with the liquid sealant. The liquid can be water (rendering it a water band pump), essential oil or a solvent, dependant on the application.