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Operating torque characteristics of the stop valve: The characteristics of the closing torque when the medium enters the valve cavity from below the valve. During the stage when the valve begins to close from its fully open position, as the valve disc descends, a pressure difference is created in front of and behind the valve disc to prevent it from moving further down, and this resistance increases rapidly as the valve disc continues to descend. When the valve is fully closed, the pressure difference across the valve disc equals the working pressure of the medium, and this is when the resistance is greatest. Combined with the forced sealing force, the operating force at the moment the valve closes increases rapidly. During the valve opening process, the thrust generated by the medium pressure or the pressure difference before and behind the valve disc both contribute to opening the valve; therefore, the shape of the valve opening characteristic curve is similar to that of the curve in the diagram, but it lies below that curve. It should be noted that the torque at the moment of opening the valve may exceed that at the moment of closing it, as a greater static friction force has to be overcome at that time. When a globe valve is opened, the flow rate reaches its maximum when the opening height of the valve disc equals a certain percentage of the valve’s nominal diameter; this indicates that the valve has reached its fully open position. Therefore, the fully open position of a globe valve should be determined by the stroke of the valve disc. The behavior of the stop valve when it is closed and when it is opened again after being fully closed is similar to that of a gate valve with forced sealing; therefore, the closing position of the valve should be determined by increasing the operating torque to a specified value.