A liquid band vacuum pump comes with an impeller with blades mounted on a center hub located in a cylindrical body but off-set from the guts.

In Body 1 to the right, you can view the blades near the the surface of the pump are nearer to the exterior wall than at the sides and bottom level of the pump. You can see this more obviously in Figure 2.

The impeller sits between two end plates (port plates) which have shaped holes cut into them called ports.

The pump requires a liquid (also known as 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 (rendering it a water band pump), essential oil or a Dry Screw Vacuum Pumps solvent, dependant on the application.