A method of refurbishing a facility for converting hydraulic energy into electrical energy, this refurbished facility comprising: - a water passage, - a turbine with a runner of the axial flow type located within the water passage and moveable around an axis and belonging to a rotatable part of the turbine and comprising a hub and several blades connected to the hub , - a drive shaft connected to the runner, - an inner head cover located adjacent to the hub and surrounding the drive shaft and belonging to the non-rotatable part of the turbine; this method being characterized in that it includes the following steps: - Providing a first cover plate , - Providing a second cover plate , - Providing a first opening located at the inner head cover , - Providing a second opening located at the hub , - Providing a third opening located at the runner, - Connecting the first cover plate to the inner head cover , - Connecting the second cover plate to the hub , whereas the first cover plate and the second cover plate are surrounding the axis, and a part of the outer surface of the inner head cover , a part of the outer surface of the hub , the inner surface of the first cover plate and the inner surface of the second cover plate are confining an annular shaped space in order to allow a gas to flow from inside the inner head cover through the first opening , the annular shaped space and the second opening and to be discharged through the third opening into the water passage during operation of the refurbished facility. - a water passage, - a turbine with a runner of the axial flow type located within the water passage and moveable around an axis and belonging to a rotatable part of the turbine and comprising a hub and several blades connected to the hub , - a drive shaft connected to the runner, - an inner head cover located adjacent to the hub and surrounding the drive shaft and belonging to the non-rotatable part of the turbine; this method being characterized in that it includes the following steps: - Providing a first cover plate , - Providing a second cover plate , - Providing a first opening located at the inner head cover , - Providing a second opening located at the hub , - Providing a third opening located at the runner, - Connecting the first cover plate to the inner head cover , - Connecting the second cover plate to the hub , - Providing a first cover plate , - Providing a second cover plate , - Providing a first opening located at the inner head cover , - Providing a second opening located at the hub , - Providing a third opening located at the runner, - Connecting the first cover plate to the inner head cover , - Connecting the second cover plate to the hub , whereas the first cover plate and the second cover plate are surrounding the axis, and a part of the outer surface of the inner head cover , a part of the outer surface of the hub , the inner surface of the first cover plate and the inner surface of the second cover plate are confining an annular shaped space in order to allow a gas to flow from inside the inner head cover through the first opening , the annular shaped space and the second opening and to be discharged through the third opening into the water passage during operation of the refurbished facility. <EOS>