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Advanced valve sealing technology to prevent valve leakage

2014/5/12

      Goal is to design a valve manufacturing firm stem seal method , in order to meet emission guidelines. The area between the valve stem and outer seal bonnet . PTFE packing material is generally , in different arrangements designed to reduce the cycle time and the carbon or graphite relaxation and mechanical damage . Some of the spring force to tend to achieve a way to reduce the slack packaging group . This is done because the packaging load loss and increased leakage relax results. A key limitation of excessive tightening packing gland follower or excessive expansion of the liner radially packaging , thereby increasing the wear and limits the packaging dry movement, which limits the reduction .

      In addition , stem packing system , metal bellows stem seal can be used to reduce leakage . Although the package after years of development , in order to meet tight leakage , always represented the ultimate advanced metal bellows seal valve technology . Bellows seal life far more than even the most advanced packaging can achieve zero leakage. In the past, this zero stem leakage of critical applications in health and safety is the primary concern and the higher cost of the bellows is reasonable. However, in the metal bellows technology should also consider the risk to health , safety and the environment sufficient to justify the use of the best available technical solutions for any application.

      External factors that may affect the service life , including the selection of suitable materials of construction, design method is suitable for implementation , using superior manufacturing processes , sealing considerations will face adversity, and contemplative process media will have what effect on the seal .

      Metal bellows are usually austenitic stainless steel or similar corrosion resistant high strength nickel-base alloys structure . Material compatibility with process fluid in chemical resistance, design flexibility , heat resistance and fatigue life . For example , dry nitrogen showed no corrosion problem , however, when it comes in contact with normal air humidity , chlorine becomes active, and will damage the stainless steel body . For this reason, Hastelloy alloy is recommended as chlorine applications , rather than the standard stainless steel bellows .

      A suitable method of construction of the bellows is a multi-layer design of the wall. When combined with higher strength metal alloys , such multilayer metal bellows seal design work scope. Bellows manufacturing process may be formed of a metal or a desired welding pattern. Formed by the method can be achieved hydrostatic or mechanical . Many outer edge by stacking individual blade segments are welded together produce welded . As more points of failure , and the design pressure level of the bellows forming the welded bellows forming machine can not be achieved .

      Detailed attention to deal with the conditions of service will allow a better product mix in metal bellows design process. Operating pressure, must be considered when extremist forces , the need to ensure the integrity of the equipment. Multi-walled metal bellows when the pressure detected by the application, bellows valve rated pressure is greater than the risk score did not collapse. Quality metal bellows clever design has proven their ability to last for years of service . Excellence in design focuses on reducing the amount of applied pressure bellows sealed . The first way to reduce stress, reduce total valve travel , reducing movement and force. The same principle , the second method is to increase the force per unit , which in turn reduces the number of forces and stresses convolution convolution of each individual . By increasing the number of maneuver to reduce the metal bellows force .

      Another way to reduce stress on the bellows is to increase the length of the component. A typical rule of thumb is , the bellows should be 10 times the valve travel . In this manner , the bellows and enjoy life exponential growth , and give a high cycles without failure .

      Stress can also be reduced by the design . For example , the best way to strengthen the bellows through the multi-layered , but also the entire width of the wall of uniform design convolution increased wall thickness. In this way, can be constructed of metal bellows seal , to improve durability , maintainability and longevity.

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