Difference between hard-sealed gate valves and soft-sealed gate valves

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The difference between hard-sealed gate valves and soft-sealed gate valves is that, in simple terms, soft sealing involves a seal between metal and non-metal materials such as nylon or tetrafluoroethylene, while hard sealing involves a seal between metals； Soft-sealed gate valves and hard-sealed gate valves are classified based on the sealing material of their seats. In hard-sealing types, the seat material is precisely processed to ensure a high degree of fit with the valve core (sphere); common materials for this purpose include stainless steel and copper. Soft-sealing types use non-metallic materials as the sealing elements embedded in the seat, and due to the elasticity of these soft-sealing materials, the requirements for precision in processing are relatively lower compared to hard-sealing types. Drawing on the characteristics of VTON, we will describe the differences between imported soft-sealed gate valves and imported hard-sealed gate valves. I. Regarding sealing materials: 1. The sealing materials for the two are different. Soft-sealed gate valves are generally made of materials such as rubber or polytetrafluoroethylene. Hard-sealed gate valves are made of metals such as stainless steel. 2. Soft seal: In a soft seal, one side of the sealing pair is made of a metallic material, while the other side is made of an elastic non-metallic material. This type of seal offers good sealing performance, but it cannot withstand high temperatures, is prone to wear, and has poor mechanical strength. Examples include steel + rubber; steel + tetrafluoroethylene, etc. For instance, the imported elastic seat seal gate valves from Weidun VTON are typically used in environments where the temperature is below 100°C, mainly in applications involving normal-temperature water. 3. Hard seal: A seal where both sides of the sealing pair are made of metal materials or other relatively hard materials is referred to as a “hard seal”. This type of seal has poor sealing performance, but it is resistant to high temperatures, wear, and has good mechanical properties. Examples include: steel+steel; steel+copper; steel+graphite; steel+alloy steel; (the steel here can also be cast iron or cast steel, and the alloys can be those applied through cladding or spraying). For example, the imported stainless steel gate valves from Weidun VTON can be used for steam, gases, oils, and water. II. In terms of construction techniques, the operating environment in the machinery industry is complex: temperatures are often extremely low and pressures are low, the resistance of the media is high, and corrosion is severe. Advances in technology have led to the widespread use of hard-sealed gate valves. Taking into account the relationship between the hardnesses of metals, in fact, a hard-sealed gate valve is the same as a soft-sealed one only because it involves sealing between metals. The valve body must be hardened, and the valve disc and seat need to be continuously ground to achieve a tight seal. The production cycle for hard-sealed gate valves is long. III. Operating conditions: Soft seals can achieve zero leakage, while hard seals can provide either high or low levels of leakage prevention; soft seals require fire protection as they may leak at high temperatures, whereas hard seals do not leak. The hard seal of emergency shut-off valves can be used under high pressure, while the soft seal cannot. At this point, a hard-sealed gate valve from Weidun VTON is needed. Soft seals should not be used with certain corrosive media; hard seals can be employed in such cases. Fourthly, regarding operating conditions, hard seals can operate at various pressures as required, while soft seals must be fire-resistant, and individual soft seals can achieve a high level of sealing performance. At ultra-low temperatures, soft-sealed valves can experience leaks due to the properties of their materials, whereas hard-sealed valves do not have this problem. Hard-sealed valves can handle very high pressures, while soft-sealed valves cannot; for example, the Weidun VTON imported forged steel gate valves use a hard-seal design and can withstand pressures of up to 32 Mpa or 2500 LB. Due to the characteristics of the media flowing through them, soft-sealed valves cannot be used in certain situations, such as those involving corrosive media. Finally, hard-sealed valves are more expensive than soft-sealed valves. As for construction, there is not much difference between the two; the key difference lies in the valve seat – soft seals are made of non-metallic materials, while hard seals are made of metallic materials. When selecting gate valves with soft or hard seals, the main considerations are the process medium, temperature, and pressure. For media that contain solid particles, are subject to wear, or operate at temperatures above 200 degrees, hard seals are the better choice. For example, with high-temperature steam, typically around 180–350°C, a hard-sealed gate valve must be chosen. VI. Differences in price and cost: Under the same specifications and pressure conditions, with identical materials, imported hard-sealed gate valves are much more expensive than imported soft-sealed gate valves ； For example, the imported cast steel gate valve of Weidun VTON with DN100 size is 40% more expensive than the imported cast steel soft-seal gate valve with DN100 size ； If both hard-sealed gate valves and soft-sealed gate valves can be used under the given operating conditions, and cost is a factor to consider, it is advisable to choose imported soft-sealed gate valves. VII. Differences in service life: A soft seal refers to a situation where one side of the sealing pair is made of a material with relatively low hardness. Generally, the soft seal seat is constructed from non-metallic materials that possess certain strength, hardness, and temperature resistance; this results in good sealing performance and the possibility of zero leakage. However, its service life and adaptability to different temperatures are relatively poor. Rigid seals are made of metal, and their sealing performance is relatively poor, although manufacturers claim that zero leakage can be achieved. The advantage of soft seals is their good sealing performance, while the disadvantages are that they tend to age and wear out easily, resulting in a short service life. Rigid seals have a long service life, but their sealing performance is relatively inferior to that of soft seals. These two types of seals can complement each other; in terms of sealing performance, soft seals are relatively better, but nowadays hard seals also meet the required standards. Soft seals cannot meet the process requirements for certain corrosive materials, but hard seals can solve this issue! These two types of seals can complement each other; in terms of sealing performance, soft seals are relatively better, yet today hard seals also have sealing capabilities that satisfy the necessary requirements. The advantage of soft seals is their good sealing performance, while their disadvantages are that they tend to age and wear out easily, resulting in a short service life. 　　Rigid seals have a long service life, but their sealing performance is relatively inferior to that of soft seals.