A liquid band vacuum pump has an impeller with Worm Gearbox blades attached to a center hub located in a cylindrical body but off-set from the center.
In Figure 1 to the right, you can observe the blades near the the surface of the pump are closer to the exterior 
wall than at the sides and bottom level of the pump. You can see this more clearly in Figure 2.
The impeller sits among two end plates (port plates) which 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 should be partially filled up with the liquid sealant. The liquid can be water (making it a water ring pump), oil or a solvent, dependant on the application.