Why is it necessary to specify a sealing device for gate valves and globe valves

When the valve is fully opened, a sealing device that prevents the medium from leaking into the packing box is called an upper sealing device.

When the gate valve, globe valve, and throttle valve are in the closed state, the medium flow direction of the globe valve and throttle valve is from below the valve disc to above, so there is no pressure in the body cavity. When the gate valve is in the closed state, the pressure in the body cavity is lower than the working pressure, so the pressure of the medium on the packing is very small. When opened, the packing must withstand 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, and prevent the valve from leaking out. Another function of it is to fully open the valve when there is leakage at the sealing packing, so that the upper sealing part is sealed. This can loosen the packing gland or packing pressure sleeve, increase the packing, and then tighten the packing gland to ensure that the valve packing is tight and there is no leakage. Therefore, upper sealing devices should be specified for gate valves, globe valves, and throttle valves.

Of course, valves such as ball valves, butterfly valves, check valves, and plug valves do not have sealing devices due to structural reasons.