Material selection for pneumatic valve seats
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Dear experts, in clause 10.3.3.1 of SH/T 3005-2016 in this standard, the valve seats of pneumatic on-off valves are required to use either hard seals, or soft seals with a design that enables them to meet the fire resistance tests specified in API607 or API6FA standards； This standard is applicable to the petrochemical industry; in cases of fine chemical manufacturing, such as the production of resins and coatings, where the materials are flammable and explosive solvents like toluene, and the operating conditions involve normal temperature and low pressure, is it necessary to use hard-sealed valve seats in accordance with this requirement when selecting valves? The valve sealing class of PTFE seat valves can reach VI level, while the highest class for valves with hard seals is V level? A project may involve hundreds of valves; a valve with a hard-sealed seat can cost over a thousand, or even two thousand, more – the cost is really high. This standard is a recommended one for the petrochemical industry, but our project falls under the category of fine chemicals. Should we not be required to follow this standard? We welcome all experts to engage in discussions and provide guidance: 1. Can a PTFE soft seal be used? 2. Although the PTFE-sealed version has a high rating, could its durability be poor? For example, might the sealing quality decline after some time of use, leading to leakage? 3. Advantages of hard-sealed valve seats over soft-sealed valve seats. I need some advice.
1. PTFE soft seals can be used, but a comprehensive consideration of actual operating conditions and safety requirements is necessary. 2. Although PTFE seals have good sealing performance initially, they tend to age and wear over time, which can lead to a decline in their sealing ability. 3. Compared to soft-sealed valve seats, hard-sealed valve seats offer better resistance to high temperatures, wear, and chemical corrosion, but at a higher cost. .
Can a PTFE soft seal be used? In fine chemical applications such as the production of resins and coatings, although the materials used are flammable and explosive solvents, PTFE soft seals may be a viable option given the operating conditions of normal temperature and low pressure differences. PTFE possesses excellent chemical resistance, temperature resistance (from -269°C to 300°C), and good sealing properties (Grade VI). However, when using PTFE soft seals, special attention must be paid to their durability. Although PTFE itself has strong resistance to chemical corrosion, under certain extreme conditions such as high temperatures, high pressures, or the presence of solid particles in the medium, its wear may be accelerated, leading to a decline in sealing performance. Durability of PTFE seals and potential issues The durability of PTFE seals depends on various factors, such as the properties of the medium, operating conditions, and valve design. Under normal temperature and low pressure differences, PTFE seals generally exhibit good durability, but in certain special circumstances, a decline in sealing performance may occur. To ensure the reliability and durability of PTFE seals, it is recommended to regularly inspect and maintain the valves, and to replace worn-out seals in a timely manner. Advantages of hard-sealed valve seats over soft-sealed valve seats: Hard-sealed valve seats are typically made of metal or cemented carbide, offering higher wear resistance and heat resistance. Under harsh operating conditions such as high pressure, high temperature, or the presence of solid particles in the medium, hard-sealed valve seats generally offer better sealing performance and a longer service life than soft-sealed valve seats. Furthermore, hard-sealed valve seats possess good mechanical properties and sealing stability, enabling them to withstand high pressures and temperature changes without deforming or leaking. Regarding the implementation of the SH/T 3005-2016 standard, this standard is a recommended one in the petrochemical industry; however, it does not mean that fine chemical projects must be carried out in strict accordance with it. When selecting a valve, factors such as the actual conditions of the project, the properties of the medium, and the operating conditions should be taken into account to choose the most suitable type of valve and sealing method. If PTFE soft-sealed valves are used in fine chemical projects, it is recommended to take their durability and reliability into full consideration during selection, and to establish corresponding inspection and maintenance plans to ensure the proper operation of the valves and safe production. In summary, for the selection of valves in fine chemical projects, a comprehensive evaluation should be conducted based on the actual conditions of the project and the properties of the medium, in order to choose the most suitable type of valve and sealing method. Under conditions of normal temperature and low pressure difference, PTFE soft seals may be a viable option, but attention should be paid to their durability and reliability. At the same time, hard-sealed valve seats may offer better performance under certain special operating conditions.
Wow! ! ! ! Big guy, thank you so much! Benefited a great deal
Hard-sealed valves can achieve not only V-grade sealing but also VI-grade sealing as well; the difference lies in the cost. You may want to take a look at our zero-friction hard-sealed ball valves.
Normally, the hard seal rating is V level; if you manage to achieve VI level, won’t the cost be higher?
The cost of a VI-grade seal is slightly higher, but not by much. We achieve VI-grade sealing through structural modifications, rather than by focusing on the fit and smoothness of the sealing surfaces.
Sir, one more question: Clause 10.3.3.1 of SH/T 3005-2016 requires a hard seal, so using a soft-seal valve seat for Class A materials would violate those regulatory requirements, right?
I have worked in both of these industries; all the control valves used there have PTFE seals :)
Won’t I get caught for not following the rules?