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Operating characteristics of butterfly valves: The operating torque characteristic curve of butterfly valves is high in the middle and low at both ends. The reason for this phenomenon is that when the butterfly valve is in the middle position, the fluid is obstructed by the butterfly plate and flows around it, resulting in vortices being formed on both sides of the plate. These vortices generate a hydraulic torque on the butterfly plate, and it is this torque that forces the plate to close. As the butterfly valve opens or closes, the effect of the swirl generated by the fluid on either side of the valve becomes increasingly minor, until the swirl disappears; at that point, the resistance experienced by the valve also decreases, resulting in a characteristic curve that is higher in the middle and lower at the ends. As for the reason why the operating torque required to open the valve is greater than that required to close it, it is because the hydrodynamic torque exerted by the fluid on the butterfly disc always acts in the direction of closing the valve. The maximum operating torque for non-sealed butterfly valves occurs at the intermediate position, whereas the maximum operating torque for sealed butterfly valves occurs when the valve is closed, due to the need to apply a force for forced sealing. The stem of a butterfly valve only performs rotational motion; its disc and the stem itself do not possess self-locking capability. To position the butterfly valve (to stop at a specified position), one approach is to attach a reducer with self-locking capability to the valve stem. By adding such a worm gear reducer, the angular displacement can be increased to several dozen turns, while the operating torque is reduced accordingly. This allows certain operational characteristics of the butterfly valve, such as the total number of rotations and the operating torque, to be brought closer to those of other valves, facilitating its use with electric actuators. For butterfly valves with mandatory sealing, their closed position should be determined by increasing the operating torque to a specified value