System for changing over of blast furnace top pressure control

In a system for changing over control of the furnace top pressure in a blast furnace system, including a septum valve installed in a flowpath of exhaust gas from the furnace top and having a capability of controlling said top pressure, and a blast furnace gas energy recovery turbine installed in a flowpath bypassing the septum valve with a speed regulating valve installed therein upstream of said turbine, said turbine having a capability of controlling said top pressure by front pressure control, the improvement comprising furnace top pressure setter means which sets higher and lower top pressure preset values having a slight difference therebetween and wherein the higher preset value serves for control by the septum valve and the lower preset pressure valve serves for control by the turbine, and load setter means for varying the load on the turbine, whereby the predominance in controlling the furnace top pressure between said two control capabilities is automatically changed over from one capability to the other in accordance with the operation of varying the turbine load by the load setter means while the two control capabilities are maintained in operative state.