at three stages or extraction points the steam extracted from the first second and third extraction points is respectively introduced to the intermediate or low pressure feed water heater 6b the deaerator 7 and the low pressure feed water heater 6c with the extracted steam in each case passing through an extraction stop valve 12 and a check valve 11 the feed water heater 6c is provided with a feed water bypass valve 15 a feed water inlet valve 13 and a feed water outlet valve 14 in the example of fig1 two feed water heaters 6a and 6b are also provided with a feed water inlet valve 13 a feed water outlet valve 14 and a bypass line with a single bypass valve 15 the extracted steam condenses in each of the feed water heaters 6a 6b 6c by heat exchange with the feed water supplied to the boiler and the drain water condensed in the feed water heater is recirculated to the condenser 4 through a water pipe 16 the number and arrangement of the feed water heaters differs in dependence upon the output power of the steam plant and they are not limited to those shown in the drawing before explaining the preferred embodiment of the present invention the principle of the present invention will be explained with reference to fig2 in fig2 there is illustrated a simplified drawing of a turbine 20 which comprises turbine diaphragms 71 and turbine blades 72 q.