The pump has an external screw-type rotor, and an internal screw-type stator. The rotor turns eccentrically in the stator. It also has a drive shaft and a flexible shaft, to connect drive shaft and rotor. The flexible shaft consists of a technical plastic, and its central section is surrounded by a metal sleeve. The length of the flexible shaft is at least 15 times the outer diameter of the rotor, or at least 1 m. One end of the flexible shaft is in material-connection with one drive shaft end. A mechanical seal forms a shaft seal between drive shaft and pump housing.
