The conveying chamber is completely separated from the oil sumps by a space open to atmosphere. Shaft seal by a system of pressure relieved soft packings with carbon ring-labyrinth seals, and water- and oil-purged by double-acting mechanical seals. Vertical direction of flow from top to bottom. Drive directly via flexible coupling or flexible spur gear, alternatively via narrow V-belt (up to 250 kW). Designs in special materials possible.