A timing pulley liquid ring vacuum pump comes with an impeller with 
blades mounted on a center hub positioned in a cylindrical body but off-set from the guts.
In Body 1 to the proper, you can observe the blades close to the top 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 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 must be partially filled with the liquid sealant. The liquid could be water (rendering it a water band pump), oil or a solvent, dependant on the application.