| 摘要 |
A steam valve for a steam turbine includes a control valve head having a recess and a stop valve head disposed within the recess of the control valve head, both heads having sealing surfaces in opposition to a valve seat. The control valve head is displaced by a control system in accordance with steam turbine requirements. The stop valve head provides a fast-acting valve to close the steam valve in response to a turbine upset. The control system, at least during throttling operations, controls the position of the stop valve head in proportion to the position of the control valve head such that vortex flow past the surfaces and valve seat is minimized or eliminated and substantial laminar flow occurs across the sealing surfaces of the stop valve and control valve heads.
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