Stop valve torque analysis

When the stop valve starts to close from the fully open position, as the valve disc drops, the fluid creates a pressure difference before and after the valve disc to prevent the valve disc from falling, and this resistance increases rapidly as the valve disc drops. When the stop valve is fully closed, the pressure difference before and after the valve disc is equal to the working pressure of the medium, and the resistance is maximum at this time. Coupled with the forced sealing force, the operating force at the moment of closing of the stop valve increases rapidly. During the valve opening process, the thrust caused by the medium pressure or the pressure difference before and after the valve disc helps open the valve. It should be pointed out that the torque at the moment of opening the valve may exceed the torque at the moment of closing the valve, because a large static friction force must be overcome at this time. When the stop valve opens, when the opening height of the valve disc reaches 25% to 30% of the nominal diameter of the stop valve, the flow rate has reached the maximum, which means that the stop valve has reached the fully open position, so the fully open position of the stop valve should be determined by the valve disc. Determine the itinerary. The conditions when the stop valve is closed and when it is opened again after being tightly closed are similar to those of the forced sealing gate valve. Therefore, the closing position of the stop valve should be determined by increasing the operating torque to the specified value.