【Haichuan Chemical Valve Knowledge】Why is it required that gate valves have an upper sealing device?

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【Haichuan Chemical Valve Knowledge】Why is it required that gate valves have an upper sealing device? A sealing device that prevents the medium from leaking toward the packing box when the valve is fully open is called an upper sealing device. When gate valves, globe valves, and throttle valves are in the closed position, since the flow direction of the medium through globe valves and throttle valves is from below the valve disc upward, there is no pressure within the chamber. When a gate valve is closed, the pressure inside the chamber is lower than the operating pressure; therefore, the pressure exerted by the medium on the packing is very small. When it is activated, the packing area is subjected to working pressure. If an upper sealing structure is present, it prevents the pressure of the working medium from acting on the sealing packing, thereby extending its lifespan and preventing leaks from occurring in the valve. Another function of it is that, in the event of leakage at the sealing packing area, the valve can be fully opened to seal the upper sealing portion. This allows the packing gland or packing sleeve to be loosened, more packing to be added, and then the gland to be tightened again, thereby ensuring a tight seal at the valve’s packing area and preventing any external leakage. Therefore, gate valves, globe valves, and throttle valves must be equipped with an upper sealing mechanism.