In sealing material
The hard seal
of the ball valve
is the metal-to-metal seal
and the valve
body and seat are all made from metal. The precision of manufacturing and the processes are very difficult. Generally, the hard sealed ball valves
are used for those working under high pressure which is usually greater than 35Mpa. The soft seal
is the metal-to-nonmetal seal
, with nonmetal materials such as Nylon and PTFE. The hard and soft sealed ball valves have the same manufacturing standard.
Hard and soft seal are for the sealing materials of valve seats. The hard seal refers to the precise process of the valve seats’ materials to guarantee the accuracy of fit between valve spools（the ball）and valve seats. We usually use stainless steel and copper as the hard sealing materials. The soft seal refers to the sealing materials of valve seats are nonmetal. Since the soft sealing materials have certain resilience, the requirements on the processing precision of soft sealed ball valves are lower than those of the hard sealed ball valves.
The working environments of many chemical and machinery industries are very complex and most of them are with high temperatures, high pressures, big media friction resistance and strong corrosion. Nowadays, the progress of technology, the better utilization of various materials and advanced process make hard sealed ball valves widely used. In fact, the principle of hard sealed ball valves are same to that of soft sealed ball valves. However, due to the metal-to-metal seal, we have to consider factors such as the hardness of different metals, working conditions as well as the section of media, etc. Generally, we will have the hard coat treatment and polish the ball valves and valve seats to guarantee the good sealing performance. Whether choosing the soft sealed or hard sealed ball valves is decided by the process media, temperature and pressure. It is better to use hard sealed ball valves when the media contains solid particles, or the media is corrosive, or the temperature is higher than 200 degrees. We should also consider the torque of valves, choosing the fixed hard sealed valves when the torque is large. Regardless of the hard or soft sealed ball valves, both of them can reach the sealing grade 6. The production cycle of hard sealed ball valves is longer and the process is more complex, which makes manufacturing hard sealed ball valves difficult.
In service conditions
The soft sealed ball valves often can have good sealing performance while the sealing performance of hard sealed ball valves are decided by the specific sealing requirements. We should prevent fire when adopt the soft seal form since the materials of soft seal may leak at high temperatures, while the hard sealed ball valves does not have this problem. The hard sealed ball valves can be used under high pressure condition while the soft sealed ball valves can not be. The soft sealed ball valves can not be used under several conditions due to the flowing media. Finally, the hard sealed ball valves costs more than soft sealed ball valves.