Simply put, soft seal is a seal between metal and nonmetal, such as nylon tetrafluoroethylene, and hard seal is a seal between metal and metal;
Soft sealing gate valve and hard sealing gate valve are both sealing materials of valve seat. The hard seal is made of valve seat material with precision machining to ensure the matching accuracy with the valve core (ball), generally stainless steel and copper. Soft seal means that the sealing material embedded in the valve seat is non-metallic, so the requirement for machining accuracy is lower than that of hard seal valve. We will refer to the characteristics of Weidun VTON to describe the difference between imported soft seal gate valves and imported hard seal gate valves.
First, about the sealing material.
1, and their sealing materials are different. Soft-sealed gate valves are usually rubber or PTFE. Hard-sealed gate valves are made of stainless steel and other metals.
2. Soft seal: One side of the seal pair is made of metal material and the other side is made of elastic nonmetal material, which is called "soft seal". This kind of seal has good sealing performance, but it is not resistant to high temperature, easy to wear and poor mechanical properties, such as steel+rubber; Steel +PTFE, etc. For example, the elastic seat-sealed gate valve imported from Witton VTON has a service temperature generally lower than 100℃ and is used for normal temperature water.
3. Hard seal: When both sides of the seal pair are made of metal or other hard materials, it is called "hard seal". This kind of seal has poor sealing performance, but high temperature resistance, wear resistance and good mechanical properties, such as steel+steel; Steel+copper; Steel+graphite; Steel+alloy steel; The steel here can also be cast iron, cast steel, alloy steel or surfacing and spraying alloy. For example, Weidun VTON imported stainless steel gate valves can be used for steam, gas, oil and water.
Second, the construction technology
The task environment of machinery industry is complex, many of which are ultra-low temperature and low pressure, and the medium has great resistance and strong corrosiveness. Now the technology has been improved, which makes the hard seal gate valve widely used.
Considering the hardness connection between metals, in fact, the hard seal gate valve is the same as the soft seal gate valve only because it is a metal-to-metal seal. The valve body is required to be hardened, and the valve plate and valve seat should be continuously polished to achieve sealing. Hard-sealed gate valves have a long production cycle. ?
Third, the conditions of use
Sealing effect Soft seal can achieve zero leakage, and hard seal can be high or low according to requirements;
The soft seal needs fire protection, and it will leak at high temperature, but the hard seal will not. Emergency cut-off valve can use hard seal under high pressure, but not soft seal. At this time, it is necessary to use the hard seal gate valve of Weidun VTON.
Soft seal is not suitable for some corrosive media, and hard seal can be used;
Fourth, the manipulation conditions
Hard seal should be high or low according to requirements; The soft seal must be fireproof, and the single seal of the soft seal can reach a high level. Because at ultra-low temperature, the material of soft seal will leak, while the hard seal does not have this problem; Hard seal can be used for high pressure, but soft seal can't. For example, the forged steel gate valve imported from Weidun VTON adopts hard seal, and the pressure can reach 32Mpa or 2500LB. Due to the properties of flowing media (such as some corrosive media), soft seals cannot be used in some places; Finally, hard sealing valves are more expensive than soft sealing valves. As for the structure, there is little difference between them. What matters is the difference of valve seats. Soft seal is nonmetal, and hard seal is metal.
Five, the above equipment selection
The selection of soft and hard sealing gate valves mainly depends on process medium, temperature and pressure. Generally, the medium contains solid particles or is worn or the temperature is higher than 200 degrees, so it is best to choose hard seal. For example, high-temperature steam is generally around 180-350℃, so hard-sealed gate valves must be selected.
Sixth, the difference between price and cost.
Under the same caliber, pressure and material, the imported hard seal gate valve is much more expensive than the imported soft seal gate valve; For example, the imported cast steel gate valve DN 100 of Weidun VTON is 40% more expensive than the imported cast steel soft seal gate valve DN 100; If both hard seal gate valves and soft seal gate valves can be used under working conditions, when considering the cost, try to choose imported soft seal gate valves.
Seven, the difference of service life
Soft sealing means that one side of the sealing pair is made of low hardness material. Generally speaking, the soft sealing seat is made of nonmetallic materials with certain strength, hardness and temperature resistance, which has good sealing performance and can achieve zero leakage, but its service life and adaptability to temperature are relatively poor. Hard seal is made of metal, and its sealing performance is poor, although some manufacturers claim that it can achieve zero leakage.
The advantage of soft seal is good sealing performance, but the disadvantage is that it is easy to age and wear and has a short service life. Hard seal has a long service life, but its sealing performance is relatively worse than that of soft seal. These two kinds of seals can complement each other. Soft seal is relatively good in sealing, but now hard seal can also meet the corresponding requirements.
Soft seal can't meet the technological requirements of some corrosive materials, but hard seal can solve it!
These two kinds of seals can complement each other, soft seal is relatively good in sealing, but now hard seal can also meet the corresponding requirements!
The advantage of soft seal is good sealing performance, but the disadvantage is that it is easy to age and wear and has a short service life.
Hard seal has a long service life, but its sealing performance is relatively worse than that of soft seal.