|Nominal diameter (mm)||Nominal pressure (MPa)|
Note: The operating torque of the gate valve provided in the table has not been measured and calculated theoretically, but is empirical data under general applicable conditions and is for reference only.
whengateWhen the opening of the gate valve is above 10%, the axial force of the gate valve, that is, the operating torque of the gate valve does not change much. When the opening of the gate valve is lower than 10%, due to the throttling of the fluid, the pressure difference between the front and back of the gate valve increases. This pressure difference acts on the gate plate, so that the valve stem needs a large axial force to drive the gate plate, so within this range, the operating torque of the gate valve varies greatly. The gate valve with elastic gate requires a larger operating torque when it is close to closing than that with rigid gate.
When the gate is closed, different situations will occur due to the different sealing methods of the sealing surface.For self-sealing gate valves (includingFlat gate valve), when the valve is closed, the sealing surface of the gate is just aligned with the sealing surface of the valve seat, which is the fully open position of the gate valve. However, this position cannot be monitored under the operating conditions of the gate valve, so in actual use, the position where the gate valve is closed to the dead point is taken as the fully closed position of the gate valve. It can be seen that the fully closed position of the self-sealing gate valve is determined by the position of the gate (that is, the stroke). For the forced sealing gate valve, the gate must apply pressure to the valve seat when closing. This pressure can ensure that the sealing surface between the gate and the valve seat is strictly sealed, which is the sealing force of the forced sealing gate valve. 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 torque transmitted by the stem nut is larger than the torque during the operation of the valve. It can be seen that for a gate valve with forced sealing, the fully closed position is determined according to the torque on the stem nut.
After the gate valve is closed, due to the change of medium or ambient temperature, the thermal expansion of the gate valve parts will increase the pressure between the gate and the valve seat, which will be reflected on the stem nut, which will make it difficult to open the gate valve again. Therefore, the torque required to open the gate valve is larger than the torque required to close the gate valve. In addition, for a pair of sealing surfaces that are in contact with each other, the coefficient of static friction between them is also larger than the coefficient of dynamic friction. Movement requires a large force to overcome the static friction; due to temperature changes, the pressure between the sealing surfaces increases, and the static friction that needs to be overcome also increases, so that when the gate valve is opened, the torque applied to the stem nut Sometimes it grows a lot.