the present invention relates to a control system for controlling injection and extraction of steam in a steam turbine , the same valves being used both for injection of steam to the turbine and for extraction of steam from the turbine . the valves commonly used for injection and extraction are controlled to be timely opened and closed in dependence on the pressure conditions at injection points and extraction points , respectively , in the turbine and on the pressure prevailing in a process network connected to the valves such that injected or extracted steam is utilized in an optimal manner .