Pressure booster (1) for boosting the pressure of petroleum fluids, produced water or seawater, comprising a pressure booster (2) with a motor (3), a rotatable motor shaft (4) and a rotatable pump or compressor shaft (5) where the pressure booster in the form of a centrifugal pump (2) or compressor is arranged. The pressure booster further comprises: a hydraulic variable speed drive (6) arranged between the motor and the pressure booster, the hydraulic variable speed drive comprising an impeller (7) and a turbine (8), wherein the impeller of the hydraulic variable speed drive is arranged on the motor shaft and the turbine of the hydraulic variable speed drive is arranged on the pump or compressor shaft, a common driver side fluid (10) for cooling, lubricating, flushing and powering of the hydraulic variable speed drive, and cooling, lubricating and flushing of the motor and bearings, circulated by one of an impeller (9) on the motor shaft, a pump and a hydraulic power unit, a control system (11) for controlling the coupling of the motor shaft to the pump or compressor shaft by the hydraulic variable speed drive, wherein the motor shaft drives the pump or compressor shaft via the hydraulic variable speed drive.

A device for changing a pump unit of a centrifugal pump is proposed. The centrifugal pump includes the pump unit and a stator extending in an axial direction. A cup-shaped recess is provided at the first axial end of the stator into which the pump unit is capable of being inserted. The device includes an actuating device with which a mechanical force is capable of being exerted on the pump unit. The mechanical force acts in the axial direction and is directed in such a way that it separates the pump unit from the stator in the axial direction.