Main material used for sealing ring of seat on stainless steel ball valves is PTFE. PTFE has inertia to almost all of chemical substances. Sealing features include low friction coefficient, stable performance, ageing resistance, wide operating temperature range and good sealing. However, the physical features of PTFE used for stainless steel ball valves contain high expansion coefficient, sensitivity to cold flow and bad thermal conductivity. So, design should be based on those physical features. Plastic materials of seat also contain PTFE, nylon and other materials. But, when sealing materials harden, the reliability of sealing may be destroyed, especially under low differential pressure. What’s more, synthetic rubbers such as chemigum can also be used as sealing materials of seat. However, the applicable media and temperature range are limited. Moreover, if media have no lubrication, synthetic rubbers can stick ball easily. 

 

Stainless steel flanged ball valves have simple structure. In general, the sealing ring is flexible, convenient for disassembling and replacing. When the valves are fully on or off, sealing faces on ball and seat are isolated from media. Media cannot corrode sealing face when passing through. Stainless steel flanged ball valves have wide scope of application.  

 

Each of trunnion stainless steel ball valves has a floating seat. The seat moves when suffering from media pressure, pressing sealing ring to ball for sealing. In general, the upper and downer axle of ball is equipped with bearing. The valves have low torque, suitable for high pressure and large dimension valves. But for reducing torque of ball valves and improving reliability of sealing, special lubricating oil is pressed between sealing faces to form a lever of oil film, improving sealing and decreasing torque. This kind of valves is more suitable as high pressure and large dimension ball valves.