Abstract: Multiple stage centrifugal pumps have a plurality of rotors arranged on a drive shaft are shown. At least one rotor is formed as a hollow shaft which is rotatably journalled on the drive shaft and which rotates with a speed of rotation n2 which is different from the speed of rotation n1 of the drive shaft. The hollow shaft is driven by a mechanical converter which takes up mechanical power from the drive shaft in the housing and gives it off at a different speed of rotation n2 to the hollow shaft in such a manner that the speed of rotation of a rotor of the first stage is lower in order to produce a lower NPSHR value for the multiple stage pump.

Abstract: A pressure compensation system for a rotary pump prevents axial displacement of the pump shaft. The pump includes a shaft rotatable about a major axis extending centrally of the shaft, at least one impeller attached to the shaft, and a pump housing for enclosing the shaft and at least one pump impeller for generating fluid pressure for pumping upon rotation of the shaft and the at least one impeller. In these pumps, the fluid pressure can exert an axial thrust along the major axis of the shaft. Therefore, such pumps include means for thrust compensation during rotation of the shaft. The improvement in the means for thrust compensation includes a first set of permanent magnets arrayed around and attached to the shaft and a second set of permanent magnets arrayed on the pump housing. The second set of permanent magnets magnetically attracts the first set of permanent magnets to hold the shaft and the at least one impeller at a fixed position along the major axis of the shaft with respect to the pump housing.