FLUID VALVE ASSEMBLY, PROCESS VALVE POSITIONER AND USE OF A FLUID VALVE ASSEMBLY IN CONTROL OF A PROCESS VALVE

摘要

A fluid valve assembly (60) comprises a central bore (202) and a stem (203) axially-movable within the central bore and actuated by an axial pilot force (F_pil) and an axial counter force (F_sup). An inner supply pressure chamber (202E) is provided to retain a stabilized supply pressure providing the axial counter force affecting on the stem. A seal member (603) is arranged coaxially with the stem between the inner supply pressure chamber and an outer supply pressure chamber which is connected to a supply pressure input line (S). A metering edge (PR3,PS3) is arranged coaxially with the stem to control fluid flow from the outer supply pressure chamber to an actuator chamber (202D). Means (605) are provided to stabilize the supply pressure in the inner chamber against sudden pressure drops in the outer supply pressure chamber.