COMBINED STOP AND INTERCEPT VALVE FOR STEAM TURBINES

A combined stop and intercept valve is provided for controlling steam flow from a high-pressure steam turbine to a low-pressure steam turbine and comprises a substantially cylindrical casing having two identical butterfly discs fixed to rotatable shafts and disposed within the casing one immediately downstream of the other. Under normal operating conditions, both the stop (upstream) and intercept (downstream) valves are opened providing a relatively unrestricted passage for the flow of steam. During a turbine overspeed condition when the turbine speed reaches 103% of rated speed, the intercept valve closes substantially all the way. The stop valve backs up the intercept valve. Should the turbine speed reach 108% of rated speed, the stop valve closes completely shutting off the flow of steam to the low-pressure turbine. When opened, the discs partially overlie each other so that any wakes in the stream flow produced by the stop disc will not cause the intercept disc to flutter. The interior of the casing is provided with annular grooves which receive valve seats with which the discs mate in a face sealing arrangement. The positions of the seats in the grooves may be adjusted in an axial direction to maintain optimum sealing with the discs when the shafts flex under the pressure of the steam flow.