A liquid band vacuum pump has an impeller with blades mounted on a center hub positioned in a cylindrical body but off-set from the center.
In Determine 1 to the proper, you can view the blades close to the the surface of the pump are closer to the outside wall than at the sides and bottom level of the pump. You can see this more clearly in Cast Iron Figure 2.
The impeller sits between two end plates (port plates) that have shaped holes cut into them called ports.
The pump takes a liquid (also called the sealant) to create vacuum the following. Before you start the pump, it must be partially filled with the liquid sealant. The liquid can be water (making it a water ring pump), oil or a solvent, depending upon the application.