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Operating torque characteristics of ball valves: The curve showing the operating torque characteristics of ball valves is quite similar to that of butterfly valves, and this is also due to the effect of swirl generated when the flow direction of the fluid inside the sphere changes. The effect of the swirl gradually decreases as the valve is opened or closed. To move a ball valve from fully open to fully closed, the valve stem needs to rotate by 90 degrees; therefore, a mechanical limit is required for the ball valve. The open and closed positions of a ball valve should be determined by the rotation angle of the valve stem; therefore, ball valves are positioned based on their stroke. II. The main structure of the electric actuator for operating thrust valves: one type does not have a thrust disc, and in this case torque is delivered directly ； One type is equipped with a thrust disc; in this case, the output torque is converted into output thrust through the valve stem nut in the thrust disc. The concept of the stem coefficient is introduced when converting the output torque into output thrust. The ratio of the output torque to the output thrust is called the stem coefficient. III. Number of rotations of the output shaft The number of rotations of the output shaft of the electric actuator is related to the valve diameter, the pitch of the valve stem, and the number of threads; it is calculated using the following formula: M = H / ZS, where M represents the total number of rotations required by the electric actuator ； H—The opening height of the valve, that is, the full stroke of the valve’s operating element (mm) ； Z—Pitch of the valve stem thread (mm) ； S—Number of thread turns on the valve stem. IV. Valve stem diameter: For multi-turn lift-type valve stems, if the maximum valve stem diameter permitted by the electric actuator is smaller than the diameter of the valve stem of the associated valve, it is not possible to assemble an electric valve; therefore, the inner diameter of the hollow output shaft of the electric actuator must be larger than the outer diameter of the valve stem of the lift-type valve. For some rotary valves and rotary stem valves among multi-rotary valves, although there is no need to consider the issue of the valve stem diameter fitting through, the diameter of the valve stem as well as the dimensions of the keys and keyways should still be taken into full consideration during selection to ensure proper operation after assembly.