1. Field of the Invention
This invention relates to fluid control valves, and more particularly, to means for providing valve-valve seat contact for valve-valve seat misalignments and for resisting valve vibration induced by fluid flowing therethrough when the valve is in an open, unengaged configuration
2. Description of the Prior Art
Large steam turbines often utilize individually actuated control valves to avoid vibration problems which occur with internal bar lift arrangements when the mass flow rate therethrough is greater than 300,000 pounds per hour. Use of individually actuated valves provides an acceptable solution if the maximum misalignment between the valve's stem and seat at the time of valve closing is not greater than 0.006 inch. Due, however, to the non-symmetric design of and differential temperatures between components thereof, integral extraction steam chests in steam turbines typically result in parallel misalignments between the valve's stem and the valve's seat of as much as 0.10 inch. Such misalignments may be partially explained by the non-symmetric design of the steam chest and the different effects the high pressure has on the structural members holding the stems and seats of the valves. Valve vibrational problems have, in the past, been reduced by utilizing guides about the valve's plug or body to prevent vibratory motion therein. Such guides are, however, not useful when misalignment between the valve plug and seat is a problem. It is, therefore, a necessity in certain circumstances to have control valves which satisfactorily operate under relatively large misalignments and are, simultaneously, resistant to fluidly imparted vibratory motion when in the open, unengaged configuration.