Turbo expander having automatically controlled compensation for axial thrust

A turbo-machine comprising

• (a) a housing;
• (b) a rotor shaft rotatably supported in said housing, said rotor shaft having first and second ends;
• (c) a centripetally flow-through expansion turbine stage comprising an inlet, an outlet, and a first rotor mounted on the first end of said rotor shaft;
• (d) a radially flow-through compressor stage comprising an inlet, an outlet, and a second rotor mounted on the second end of said rotor shaft;
• (e) a measuring system disposed in said housing for measuring an amount of axial thrust of said rotor shaft, said measuring system comprising a ring-shaped force absorber, arranged between an outer bearing ring of a roller bearing in said housing and a stop surface of the housing, said ring being arranged on a side of said housing and stressed by an axial thrust of said rotor shaft;
• (f) at least two pressure control valves installed in at least two control lines connected to either said compressor stage or said expansion turbine stage;
• and
• (g) a controller coupled to said measuring system and controlling said at least two pressure control valves;
• wherein at least one of said first and second rotors has a rear side on which a rotor piston surface is located, said rotor piston surface being acted upon by the pressure prevailing on the inlet and outlet of the stage to which the piston surface is associated;
• and
• wherein said controller actuates in response to the measured axial thrust either the pressure control valve in the control line under the higher pressure or the pressure control valve in the control line under the lower pressure, so as to maintain the measured axial thrust within a preset tolerance range by raising or reducing the pressure.