The globe valve is a forced sealing valve, so when the valve is closed, pressure must be applied to the disc to force the sealing surface to not leak. When the medium enters the valve six from below the disc, the resistance that the operating force needs to overcome is the friction force of the valve stem and the packing and the thrust generated by the pressure of the medium. The force of closing the valve is greater than the force of opening the valve, so the valve The diameter of the stem should be large, otherwise the valve stem will bend up failure. In recent years, since the emergence of self-sealing valves, the medium flow direction of the shut-off valve has changed from above the valve clack into the valve cavity. At this time, under the action of the medium pressure, the force of closing the valve is small, while the force of opening the valve is large. The diameter can be reduced accordingly. At the same time, under the action of the medium, this type of valve is also tighter. my country's valve "Sanhua" once stipulated that the flow direction of the stop valve should be from top to bottom.

When the shut-off valve is opened, when the opening height of the disc is 25% to 30% of the nominal diameter, the flow has reached the maximum, indicating that the valve has reached the fully open position. Therefore, the fully open position of the shut-off valve should be determined by the stroke of the valve disc.