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Operating torque characteristics of wedge gate valves: When the valve opening is above 10%, the axial force on the valve, that is, the operating torque of the valve, remains relatively constant. When the valve opening is below 10%, the throttling of the fluid causes an increase in the pressure difference across the gate valve. This pressure difference acts on the gate, requiring a greater axial force on the valve stem in order to move the gate; as a result, the operating torque of the valve varies significantly within this range. In the figure, the solid line represents the operating torque characteristics of a rigid gate valve ； The dashed line represents the operating torque characteristic of the gate valve with an elastic gate. As can be seen from the curve, gate valves with elastic gates require a greater operating torque when approaching closure compared to those with rigid gates. When the gate is closed, different situations arise depending on the sealing method of the sealing surfaces. For automatically sealing gate valves (including flat gate valves), when the valve is closed, the sealing surface of the gate aligns precisely with the sealing surface of the valve seat, which represents the fully closed position of the valve. However, this position cannot be monitored under the operating conditions of the valve; therefore, in practical use, the valve is closed to its lower dead center position as the fully closed position for the gate valve. It can be seen that the fully closed position of a self-sealing valve is determined by the position of the gate (i.e., its travel distance). For gate valves with forced sealing, the gate must exert pressure on the valve seat when the valve is closed. This pressure ensures a tight seal between the gate and the valve seat; it is the sealing force that enables forced-seal valves to function properly. This sealing force will continue to be exerted due to the self-locking property of the valve stem threads. Obviously, in order to provide a sealing force to the gate, the torque transmitted by the valve stem nut is greater than the torque during valve operation. It can be seen that for gate valves with forced sealing, the fully closed position of the valve is determined by the magnitude of the torque applied to the valve stem nut. After the valve is closed, changes in the temperature of the medium or the surrounding environment can cause thermal expansion of the valve components, which increases the pressure between the gate and the seat. This, in turn, affects the valve stem nut and makes it difficult to reopen the valve. Therefore, the torque required to open the valve is greater than the torque required to close it. Furthermore, for a pair of sealing surfaces in contact with each other, the coefficient of static friction between them is also greater than that of kinetic friction; to bring about relative motion between them from a stationary state, a larger force must be applied to overcome the static friction ； Due to temperature changes, the pressure between the sealing surfaces increases, and the static friction force that must be overcome also increases. As a result, when opening the valve, the torque that needs to be applied to the valve stem nut can sometimes increase significantly.