To prevent leakage of vapor by opening a centrifugal valve when the rotational speed of a rotator is lower than a specified level, i.e., when steam is passed at the time of starting, thereby discharging condensate from a steam passage in order to prevent unbalance vibration and closing the centrifugal valve when the rotational speed of the rotator is higher than the specified level.

When a dry roll 1 is started, steam is condensed to produce water. The water is passed from a steam passage through an opening 18, a large diameter hole 13, a sheet face 14, a small diameter hole 12 and a drain passage and discharged to the outside of the dry roll 1. Since condensate does not stand in the dry roll 1 under low speed rotational state, unbalance vibration of the dry roll 1 can be prevented. When warm-up with steam is continued and rotation is increased upon temperature rise of the dry roll 1, a centrifugal force being applied to a ball valve 16 increases and the ball valve 16 is removed from a permanent magnet 17 and pressed against the sheet face 14 thus closing the small diameter hole 12. Consequently, the steam can be prevented from leaking to the outside of the dry roll 1 under high speed rotational state.