Hard Seal Ball Valves and Soft Seal Ball Valves
Hard seal ball valves and soft seal ball valves have several differences, including structure, materials and standards.
Soft sealing materials
In terms of sealing materials used in ball valves, hard seal refers to the materials of seat having been processed precisely to ensure coordinating precision between seat and core. Stainless steel and copper are in common use. Soft seal means that sealing materials of seat is non-metal materials. Due to soft sealing materials having elasticity, machining precision
is lower than that of hard sealing.
Structure
Hard seal of ball valves is sealing between metal and metal. Both core and seat are made from metal materials. Machining precision and technologies are quite difficult. In general, hard seal ball valves are used under high pressure, higher than 35MPa. Soft seal is sealing between metal and nonmetal such as nylon and PTFE. They share the same manufacturing standards.
Manufacturing techniques
Environments include high temperature and pressure, high frictional resistance of media, strong corrosion which are quite complicated. Due to manufacturing techniques development, materials are used better and machining also can keep up. Therefore, hard seal ball valves have been widely applied.
In fact, hard seal ball valves have the same sealing principles as seal ball valves. Owing to metal-to-metal sealing, hardness between metal and metal, operating conditions and media should be taken into consideration. In general, ball valves are required to be treated by harden. Core and seat need to be grinded constantly to realize sealing.
Hard seal ball valves have long production cycle and complex processing procedures. So, it is not easy for manufacturing hard seal ball valves.
Selection
Choosing hard or soft seal ball valves mainly depends on media, temperature and pressure. In general, hard seal ball valves have better to be used because of media containing solid particle or having abrasion or the temperature higher than 200 degrees centigrade. For valves having high differential pressure, torque also should be considered. Trunnion hard seal ball valves are suitable for large torque.
In short, valves have high quite high technical content. Various aspects must be noticed. Different working conditions require different valves and sealing rings.