Angle globe valve is a forced sealing valve, so when the valve is closed, pressure must be applied to the valve disc to force the sealing surface not to leak. When the medium enters valve VI from below the valve disc, the resistance to be overcome by the operating force is the friction force between the valve stem and the packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve, so the diameter of the valve stem should be larger, otherwise the failure of valve stem jacking will occur.
After the emergence of the self sealing valve, the medium flow direction of the stop valve changes from above the valve disc to enter the valve chamber. At this time, under the action of medium pressure, the force to close the valve is small, while the force to open the valve is large, and the diameter of the valve stem can be reduced accordingly. At the same time, under the action of medium, this form of valve is also more tight. The “three modernizations” of valves in China once stipulated that the flow direction of stop valves should be from top to bottom.
