Sealing and strength performance are basic and the most important performance for valves. Sealing of
valves can be divided into internal sealing and external sealing. Internal sealing is the sealing between the valve clack and the valve seat; external sealing is the sealing between the moving part of the valve stem and the valve bonnet, the valve body and the valve bonnet as well as the valve body and the connecting part of the pipeline.
Valves are required to not only have good sealing performance, but also be safe when they are in operation.
If leakages happen due to poor sealing performance or the part is damaged due to poor strength, different degrees of economic losses will be caused. Transporting toxic, flammable, explosive or highly corrosive fluids may lead to serious accidents. In order to ensure sealing performance and strength of
valves, we also need to correctly choose the material besides reasonably designing the structure and making sure of quality of the process based on the related standard requirements.
Usually, brass or bronze is adopted for the sealing surface of the low-pressure valve; stainless steel is used for high and medium pressure valves and cobalt based hard alloy is used for high pressure valves, medium pressure valves and high temperature valves which have high requirements. Polymeric materials have been widely used for valves. For example, PTFE is mainly adopted for valve seats of
ball valves, and a variety of rubber materials is adopted for sealing rings of butterfly valves and diaphragms of diaphragm valves. These materials have better sealing performance than those of metals at the applicable temperature range.
With the development of the modern nuclear industry, the petrochemical industry, the electronics industry, the aerospace industry, automatic control of process technology and long-distance fluid transportation, modern cryogenic valves, vacuum valves,
valves for nuclear industries and various regulating valves are further developed. More and more driving devices are applied to remote control and program control.
The future development trend of the
valve is to expand parameters of the valve product, to improve structures and service lives of
valves, adopting new materials and new processes, and to develop valves with energy saving, labor saving and automatic control and series of special valves such as cryogenic valves and vacuum valves used for liquid oxygen, liquid hydrogen and liquefied natural gas and nuclear industrial valves such as safety valves, regulating valves, steam traps and valve drives.
