Leakage of valves in the life, production is very common, ranging from waste or cause danger to life, such as tap water valve leaks, heavy lead to serious consequences, such as the chemical industry is toxic, harmful, flammable, explosive and Corrosive media leak, etc., serious threat to personal safety, property safety and environmental pollution accidents. A relying on external rotation of the drive open and close the valve is designed with a sealing device is used in the packing culvert installed a certain number of packing rings, so as to achieve the sealing effect, but what about the sealing? Leakage of the valve packing is the most prone to leakage in the valve of the site one, but the reason there are roughly two reasons. First, the filler reasons. Fillers are now mainly used are: 1. Asbestos, due to the existence of chloride ion asbestos stem corrosion of the material, asbestos contains carcinogens, endangering human health, the state has taken some products banned or used less; Synthetic resins and synthetic fibers, some of these products are limited in the scope of use, such as the use of pure polytetrafluoroethylene temperature must be ≤ 150 ℃, polytetrafluoroethylene ≤ 250 ℃, polytetrafluoroethylene grain filler compensation performance Poor, only applies to low pressure valves, PTFE fiber, carbon fiber or both mixed filler, and the price is too high, unfavorable promotion; 3. Expanded graphite, then there will be serious electrochemical corrosion. Second, the problem of corrosion is also one aspect of the reasons. Corrosion conditions are: 1. Stem of the natural oxidation and corrosion, as the valve stem filler at the table is oxidized, generating ferrosoferric oxide (rust) off, resulting in valve stem thinning, caused by leakage; 2. Asbestos packing chloride ion corrosion caused by leakage; 3. Graphite filler stainless steel corrosion; 4. Medium on the stem of corrosion and so on.