The hydrodynamic shaft seal is an almost forgotten but very effective principle. It is eminently suitable for operation with liquids loaded with solid material. The hydrodynamically sealed pump has an impeller with back vanes and additionally, depending on the suction head, a high performance seal expeller. This sets an equal pressure opposing the residual or pumping pressure. Almost all Bungartz pumps combine the hydrodynamic shaft seal as a primary seal with a downstream, depressurised secondary sealing (packed gland, lip seal, mechanical seal or magnetic drive).