Vacuum shut-off valve

The opening and closing parts of a vacuum stop valve (Globe Valve) are plug shaped valve discs, with a flat or conical sealing surface. The valve disc moves in a straight line along the centerline of the fluid. The movement form of the valve stem, (common name: non rising stem), also known as the lifting rotating stem type, (common name: rising stem) globe valve refers to a valve where the closing part (disc) moves along the centerline of the valve seat. According to the movement of the valve disc, the change in the valve seat opening is directly proportional to the valve disc stroke. Due to the relatively short opening or closing stroke of the valve stem and the highly reliable cut-off function, as well as the proportional relationship between the change of the valve seat opening and the stroke of the valve disc, this type of valve is very suitable for regulating flow. Therefore, this type of valve is very suitable for cutting, adjusting, and throttling purposes. The shut-off valve belongs to the forced sealing type 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 the valve from below the valve disc, the resistance that needs to be overcome by the operating force is the friction force between the valve stem and 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 the valve stem top bending will occur. In recent years, since the emergence of self sealing valves, the medium flow direction of the shut-off valve has shifted from above the valve disc to 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 correspondingly reduced. At the same time, under the action of the medium, this type of valve is also relatively tight. The "three modernizations" of valves in China once stipulated that the flow direction of shut-off valves should be from top to bottom. When this valve is to be horizontally installed and the shut-off valve is opened, the opening height of the valve disc is 25% to 30% of the nominal diameter, and the flow rate has reached, indicating that the valve has reached the fully open position. So the fully open position of the shut-off valve should be determined by the stroke of the valve disc.