A liquid band Low Backlash Reducers vacuum pump comes with an impeller with blades mounted on a center hub situated in a cylindrical body but off-set from the guts.
In Determine 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 of the pump. You can observe this more obviously 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. Prior to starting the pump, it should be partially filled with the liquid sealant. The liquid can be water (rendering it a water band pump), oil or a solvent, depending upon the application.