The hard seal of ball valve is the seal between metal and metal, and the sealing ball and valve seat are both metal. The machining accuracy and process are difficult. It is generally used in high pressure, usually above 35MPa. Soft seal refers to the seal between metal and non-metal, such as nylon and tetrafluoroethylene. The manufacturing standard is the same.
On the sealing material
The soft and hard seal is for the sealing material of the valve seat. The hard seal is precisely processed with the valve seat material to ensure the matching accuracy with the valve core (ball). Generally, there are stainless steel and copper. Soft sealing refers to that the sealing material embedded on the valve seat is non-metallic material. Because the soft sealing material has a certain elasticity, the requirements for processing accuracy are relatively low for hard sealing.
Due to the complex working environment in many chemical and mechanical industries, many are high temperature and high pressure, the friction resistance of the medium is large, and the corrosion is strong. Now the technology has progressed, the application of various materials is relatively good, and the processing and other aspects can keep up, so that the hard sealed ball valve has been widely promoted.
In fact, the principle of hard seal ball valve is the same as that of soft seal, but because it is the seal between metals, it is necessary to consider the hardness relationship between metals, as well as working conditions, what medium to use, etc. Generally, hardening treatment is required, and the ball and valve seat should be continuously ground to achieve sealing. Hard sealed ball valve has a long production cycle and complex processing. It is not easy to make hard sealed ball valve.
In terms of service conditions
Generally, the soft seal can reach a high level, while the hard seal can be high or low according to the requirements; The soft seal needs fire prevention, because under high temperature, the material of the soft seal will leak, while the hard seal does not have this problem; Hard seal can generally do high pressure, but soft seal can't; Due to the problem of the flowing medium, the soft seal cannot be used in some occasions (such as some corrosive media); Rear hard seal valves are generally more expensive than soft seal valves. As for manufacturing, there is little difference between the two, mainly the difference between the valve seat. The soft seal is non-metallic and the hard seal is metallic.
On equipment selection
The selection of soft and hard sealing ball valves is mainly based on the process medium, temperature and pressure. Generally, the medium contains solid particles or has wear or the temperature is higher than 200 degrees. It is good to choose hard sealing. The valve with a diameter greater than 50 has a large differential pressure. It is also considered to open the valve torque. When the torque is large, fixed hard sealing ball valves should be selected, and the sealing grade of both soft and hard sealing can reach grade 6