There are three sealing parts of the valve: the contact between the opening and closing parts and the two sealing surfaces of the valve seat; The matching place of packing, valve stem and stuffing box; The joint between valve body and valve cover. One of the previous leakage is called internal leakage, which is usually said to be not closed tightly, it will affect the ability of the valve to cut off the medium. For block valves, internal leakage is not allowed. The leakage of the latter two places is called external leakage, that is, the medium leaks from the inside of the valve to the outside of the valve. Leakage will cause material loss, pollute the environment, and even cause accidents. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance.
