When the valve is fully open, a sealing device that prevents the medium from leaking to the packing box is called the upper sealing device.

    When the gate valve, stop valve, throttle valve is closed, because the medium flow direction of the stop valve and throttle valve is flowing upward from below the valve disc, there is no pressure in the body cavity, and the pressure in the body cavity is lower than the working pressure when the gate valve is closed, so the pressure of the medium on the packing is very small. When opened, the packing should bear the working pressure, if there is an upper sealing structure, it can prevent the working medium pressure from acting on the sealing packing, extend the life of the sealing packing, so that the valve does not have external leakage. Another function of it is that when there is leakage in the sealing packing, the valve can be fully opened to seal the upper sealing place, so that the packing cover or the packing press sleeve can be loosened, the filler can be increased, and the filling cover can be pressed tightly, so as to ensure that the packing place of the valve is dense and there is no leakage. Therefore, the gate valve, the globe valve and the throttle valve should be provided with the sealing device.

    Of course, for ball valves, butterfly valves, check valves, plug valves and other valves due to structural reasons, there is no upper sealing device.