◆ When the opening of the gate valve is over 10%, the axial force of the gate valve, that is, the operating torque of the gate valve does not change much. When the gate valve opening is less than 10%, due to the throttling of fluid, so that before and after the gate valve pressure increases. This pressure difference effect on the gate, so that the valve stem requires a larger axial force to drive the gate, so in this range, the gate valve operating torque changes relatively large. Flexible gate valve, close to close the operating torque required to be greater than the rigid gate. ◆ When the gate is closed, different conditions will result due to different sealing methods of the sealing surface. For automatic sealing gate valve (including flat gate valve), when the valve is closed, the sealing surface of the gate plate is exactly aligned with the sealing surface of the valve seat, that is, the full opening position of the gate valve. However, this position can not be monitored under the operating conditions of the gate valve. Therefore, in actual use, the position of the gate valve close to the dead center serves as the gate valve closed position. Thus, the fully closed position of the automatically sealed gate valve is determined by the position of the gate (ie, travel). For forced sealed gate valves, the gate must be closed to apply pressure to the valve seat. This pressure can ensure that the sealing surface between the gate and the valve seat is strictly sealed, is the seal force of the compulsory seal gate. This sealing force will continue to work due to the self-locking of the stem nut. Obviously, in order to provide sealing force to the gate, the stem nut transmits more torque than the valve during operation. Thus, for the mandatory seal gate valve, the fully closed position is determined by the size of the stem nut torque suffered. ◆ After the gate valve is closed, due to the change of medium or ambient temperature, the thermal expansion of the gate valve components will cause the pressure between the gate plate and the valve seat to become larger. When the valve stem is reflected on the valve stem nut, it is difficult to open the gate valve again. Therefore, the torque required to open the gate valve is greater than the torque required to close the gate valve. In addition, for a pair of sealing surfaces in contact with each other, the coefficient of static friction between them is also greater than the coefficient of dynamic friction so that they will be relatively stationary Exercise, the need to exert greater force to overcome the static friction; due to temperature changes, so that the pressure between the sealing surface becomes larger, the static friction to be overcome also will be larger, so that when the valve is opened, the torque exerted on the stem nut Sometimes it will increase a lot. Gate valve torque reference table Nominal diameter (mm) Nominal pressure (MPa) 0.25 0.6 1.0 1.6 2.5 4.0 6.4 10.0 16.0 20.0 32.0 Torque (N · m) 50 25 25 50 50 200 65 25 50 50 50 600 80 50 50 50 50 1200 125 50 500 900 - - 150 - - 1200 1800 - - 2500 - - - 1200 1800 - - - - 1800 2500 - - - - - 5000 - - - - - 5000 - - - - 1800 - 3500 - 6500 - - - - 1800 - 5000 - 8000 - - - - 2500 - 8000 - - - - - - 2500 - - - - - - - - 2500 - - - - - - - 3500 - - - - - - - 5000 - - - - - - - - Note: The gate valve operating torque provided in the table without physical determination and theoretical calculations, is generally applicable to the conditions Experience data, for reference only
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