A safety valve for use in a wellbore formed in an earth formation, comprising a valve body having a fluid passage for passage of a stream of hydrocarbon fluid flowing from the earth formation via the wellbore to the earth surface,SAFETY VALVES a closure member movable relative to the valve body between an open position in which the fluid passage is open and a closed position in which the closure member closes the fluid passage, and an activating device for selectively subjecting the closure member to a drag force of selected magnitude,Balance Valves the drag force being exerted by the stream of fluid and inducing the closure member to move from the open position to the closed position thereof. The safety valve further comprises control means for controlling the activating device to subject the closure member to said drag force.Instrumentation Ball Valves The present invention relates to a safety valve for use in a wellbore formed in an earth formation, comprising a valve body having a fluid passage for passage of a stream of hydrocarbon fluid flowing from the earth formation via the wellbore to the earth surface, a closure member movable relative to the valve body between an open position in which the fluid passage is open and a closed position in which the closure member closes the fluid passage. The safety valve serves to shut down production from the wellbore either by control from surface or automatically in case of undesirable flow conditions. The latter situation occurs for example in case of increased hydrocarbon fluid flow rate as a result of an accident at a surface production facility. Therefore it is generally aimed to design a safety valve for a wellbore such that the valve closes upon the flow rate in the wellbore reaching a selected threshold flow rate.

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