First of all, whether it is a ball valve or a butterfly valve, etc., there are soft and hard seals, take the ball valve as an example, the use of soft and hard seals of ball valves is different, mainly in structure, and the manufacturing standards of valves are inconsistent.
First, the structural mechanism
The hard seal of a ball valve is a metal-to-metal seal, and both the sealing ball and the seat are metal. The machining accuracy and process are relatively difficult, and it is generally used in high pressure, usually more than 35MPa. Soft seals are seals between metals and non-metals, such as nylon\PTFE, and the manufacturing standards are the same.
Second, the sealing material
The soft and hard seal is the sealing material of the valve seat, and the hard seal is precision machined with the valve seat material to ensure the matching accuracy with the valve core (ball), generally stainless steel and copper. Soft sealing means that the sealing material embedded in the valve seat is a non-metallic material, because the soft sealing material has a certain elasticity, so the processing accuracy requirements will be lower than that of hard sealing.
Third, the manufacturing process
Due to a lot of chemical industry, the working environment of the machinery industry is more complex, 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 use of various materials is better, and the processing and other aspects can keep up, so that the ball valve with hard seal 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 a seal between metals, it is necessary to take into account the hardness relationship between metals, as well as working conditions, what medium to go, etc. Generally, hardening is required, and the ball and seat are constantly ground to achieve a seal. The production cycle of hard seal ball valve is long, the processing is more complicated, and it is not easy to do a good job of hard seal ball valve.
Fourth, the conditions of use
Soft seals can generally reach high seals, while hard seals can be high or low according to requirements; Soft seals need to be fireproof, because at high temperatures, the material of the soft seal will leak, while the hard seal does not have this problem; Hard seals can generally be made with high pressures, but soft seals cannot; Due to the problem of the medium flowing, the soft seal cannot be used in some occasions (such as some corrosive media); The last hard seal valve is generally more expensive than the soft seal valve. As for the manufacturing, there is not much difference between the two, the main thing is the difference between the valve seats, the soft seal is non-metallic, and the hard seal is metal.
Fifth, in the selection of equipment
The selection of soft and hard seal ball valves is mainly based on the process medium, temperature and pressure, the general medium contains solid particles or has wear or the temperature is higher than 200 degrees, it is good to choose hard seals, the diameter is greater than 50, the valve pressure difference is larger, and the torque of the opening valve is also considered, and the fixed hard seal ball valve should be selected when the torque is larger, regardless of the soft and hard seals, the sealing level can reach level 6.
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Post time: Nov-26-2024
