Abstract: Various implementations include electric centrifugal pump assemblies for producing oil from wells. A submersible electric motor includes a housing, a shaft inside said housing that transmits rotational power from the electric motor section to the pump section, a mechanical seal surrounding the shaft to keep a dielectric fluid inside the electric motor, and a unit for compensating the volume of the dielectric fluid. Said unit maintains a constant positive pressure and includes a spring mounted inside a metal bellows. The spring is arranged in a tensioned state inside a cavity containing dielectric fluid. The spring is rigidly fastened facing the electric motor and to the bottom of the bellows such as to be capable of axial movement. The volume compensation unit is provided with a sensor for sensing the position of the spring/bellows. The cavity is filled with a barrier fluid preventing scale build-up.

Abstract: Various implementations include electric centrifugal pump assemblies for producing oil from wells. A submersible electric motor includes a housing, a shaft inside said housing that transmits rotational power from the electric motor section to the pump section, a mechanical seal surrounding the shaft to keep a dielectric fluid inside the electric motor, and a unit for compensating the volume of the dielectric fluid. Said unit maintains a constant positive pressure and includes a spring mounted inside a metal bellows. The spring is arranged in a tensioned state inside a cavity containing dielectric fluid. The spring is rigidly fastened facing the electric motor and to the bottom of the bellows such as to be capable of axial movement. The volume compensation unit is provided with a sensor for sensing the position of the spring/bellows. The cavity is filled with a barrier fluid preventing scale build up.