The sealing performance of the valve is the valve part of the sealing ability to prevent media leaks, it is the valve of the most important technical performance indicators. Sealing valve has three parts: opening and closing pieces and valve seat sealing surface contacts between the two; and with the Department filler stem and the stuffing box; junction body and bonnet. Which is called before a leak within the leak, which is commonly known as Guan lax, it will affect the ability of the valve cut off media. For the truncated valve, the internal leakage is not allowed. Leakage after the two called the leak, that media leaks from the valve to the valve outside. Leakage will result in material losses, environmental pollution can also cause serious accidents. The explosive, toxic or radioactive medium, leakage is allowed, and therefore, the valve must have a reliable sealing performance.