A hard seal is a seal between a metal and a metal, both the seal ball and the seat are metallic. Processing accuracy and technology more difficult, generally used in high pressure, usually 35MPa above. Soft seal is a seal between metal and non-metallic, such as nylon \ tetrafluoroethylene, the standard is the same. First, the sealing material on the flexible seal valve and soft seal gate valve is the sealing material, the hard seal is the valve seat material precision machining to ensure that with the spool (ball) with the precision, there are generally stainless steel and copper . Soft seal refers to the sealing material embedded in the valve seat is non-metallic material, because the soft sealing material has a certain elasticity, so the relative precision of the machining requirements will be low. Second, the manufacturing process Due to a lot of chemical industry, machinery industry, the working environment is more complicated, many are high temperature and pressure, medium friction resistance, strong corrosive, and now the technology advances, the use of various materials is better, processing And so on can keep up, so hard-sealed ball valve has been widely promoted. In fact, the principle of hard seal valve and soft seal is the same, but because of the seal between the metal, taking into account the relationship between the hardness of the metal, as well as working conditions, what kind of medium go. Generally require hardening treatment, the ball and valve seat to be constantly grinding to seal. Hard seal gate valve production cycle is long, the processing is more complex, hard-sealed ball valve is not easy to do. Third, the use of soft seals on the general seal can reach high, while the hard seal is required on request can be high and low; soft seal requires fire protection, because at high temperatures, the soft seal material will leak, and no hard seal This problem; hard seal can generally do a very high pressure, soft seal will not work; soft seal due to the flow of media problems, some occasions can not be used (such as some corrosive media); finally hard seal valve than the soft seal Expensive. As for the manufacturing, the difference is not large, mainly the difference between the seat, soft seal is non-metallic, hard-sealed metal. Fourth, the selection of equipment above the soft and hard seal gate valve selection based mainly on process media, temperature and pressure, the general medium containing solid particles or wear or temperature is higher than 200 degrees the best selection of hard-sealed, diameter greater than 50 valve pressure more than Big also consider opening the valve torque, the torque should be used when a fixed hard seal gate valve, regardless of the seal level of soft and hard seals can reach 6.