Toyo Valve(Shanghai)Co.,Ltd

When the opening of the gate at least 10% of the axial force gate, that little valve operating torque change. When the opening degree of the valve is less than 10%, due to throttling of fluid, so that the differential pressure across the valve increases. This pressure differential acting on the shutter, so that the valve stem requires a larger axial force to drive the shutter, so in this range, the valve operating torque variation is relatively large. Flexible gate valve, shut down when approaching the desired operating torque than the rigid gate to be bigger.

When the damper is closed, due to the different ways the sealing surface of the sealing, will produce different situations. For the self-sealing valve (including flat gate), when the valve is closed, the sealing surface is exactly aligned gate valve seat sealing surface, that is, the gate valve fully open position. But this position in the valve operating conditions is not monitored, so in actual use, the valve is closed to the dead center position as the valve fully closed position. Thus, self-sealing valve is fully closed position by gate position (ie stroke) determined. For mandatory sealed valve, must exert pressure on the seat when the gate is closed. This pressure can ensure the sealing surfaces between the gate and the seat tight seal, is mandatory sealed valve sealing force. This sealing force due to the self-locking nut stem will continue to do with. Clearly, in order to provide the sealing force gate, stem nut torque transmission than the valve operation of torque. Thus, for mandatory sealed valve, fully closed position is suffered by stem nut torque to determine the size.

After the gate valve is closed, since the medium or the change in ambient temperature, pressure and thermal expansion causes the gate member between the valve seat becomes large, reflected on the stem nut, then it is difficult for this to open the valve. Therefore, the torque required to open the valve is greater than the torque required to close the valve, in addition, a sealing surface for contact with each other, the coefficient of static friction between them than the large dynamic friction coefficient, to make them produce a relatively quiescent state from movement, a large force is required to overcome the static friction force is applied; due to temperature changes, so that the sealing surface pressure becomes large, the need to overcome the static friction force become larger, so that the moment when the valve is turned on, applied to the stem nut sometimes increase a lot. Valve torque reference table Nominal Diameter (mm) Nominal pressure (MPa)