Fluorine lined butterfly valve has been widely used in devices contacting with acid and alkali of strong corrosive medium in the petroleum, chemical industry, medicine, metallurgy, electric power industries, but how to choose the right and appropriate use fluorine lined butterfly valves, according to our application experience for many years. When choosing a fluorine-lined butterfly valve, the following points for attention are put forward for the using conditions of medium temperature, pressure, differential pressure, etc.
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1. As the multi-layer soft and hard stack sealing ring is fixed to the valve plate when the valve plate is in an always-open status, the medium has a frontal brush on its sealing surface. After the soft sealing in the metal sheet is brushed and eroded, the sealing performance is directly affected.
2. Limited by the structural conditions, this structure is not suited to be made into valves that have a diameter less than DN200, because the overall structure of the valve plate is too thick and the flow resistance is too big.
3. Due to the mechanism of the rubber-lined sanitary butterfly valve, the sealing between the sealing surface of the valve plate and the valve seat is determined by the torque of the transmission device. In the positive flow state, for tube pinch valve, fluorine lined valve, exhaust valve, the higher the pressure of the medium is, the tighter the sealing squeezes. When the medium backflows, with the pressure of the medium increases, the unit positive pressure between the valve plate and the valve seat is smaller than the pressure intensity, resulting in the sealing beginning to leak.
4. High-performance fluorine-lined butterfly valve is characterized by the fact that the valve seat sealing ring is composed of a plurality of stainless steel sheets on both sides of a flexible T-shaped sealing ring.
The sealing surface of the valve plate and the valve seat is an oblique conical structure, and temperature and corrosion resistant alloy material is welded on the surface of the oblique conical structure. This structure effectively compensates the elastic deformation between the sleeve and the valve body, solves the sealing problem of the valve in the process of the two-way interchangeable medium transportation.
Using soft T-shaped multi-layer stainless steel sheets on both sides of the sealing ring has the dual advantages of metal hard sealing and soft sealing. Whether in low temperature or high-temperature conditions, both have a sealing performance of zero leakage.
Experiments suggest that in positive flow status, the pressure of the sealing surface is caused by the torque of the transmission and the effect of the medium pressure on the valve plate. When the positive medium pressure increases, the tighter the squeeze between the oblique conical surface of the valve plate and the sealing surface of the valve seat, the better the sealing effect.
When the medium backflows, the sealing between the sealing surface of the valve plate and the valve seat is determined by the torque of the transmission device. With the increase in the reverse medium pressure, the unit positive pressure between the valve plate and the valve seat is smaller than the pressure intensity.
Therefore, the utility model does not install the soft and hard multi-layer sealing ring on the valve plate as in current technologies. Rather, it is directly installed on the valve body. Adding an adjustment ring between the valve plate and the valve seat is very ideal for two-way hard sealing.
Polytetrafluoroethylene (PTFE)
PTFE has high chemical corrosion resistance, and its corrosion resistance exceeds all existing plastics, so it is known as the "King of Plastics". PTFE is resistant to corrosion by almost any concentration of strong acids, alkalis, strong oxidants and solvents, and has no effect on it even at high temperatures.
The outstanding processing performance of polytetrafluoroethylene is that it is difficult to mold and process. It has no fluidity in the molten state and cannot transform from the "high elastic state" to the "viscous flow state" above the melting temperature. It is heated to its decomposition temperature (415°C). ) cannot flow either.
Therefore, it is difficult to use PTFE to manufacture parts with complex shapes using general thermoplastic processing methods such as molding and injection. PTFE powder can only be pre-pressed into the required shape and then sintered. Its coating is very microporous and cannot be used alone as an anti-corrosion coating.
Polyperfluoroethylene propylene plastic (FEP)
Soluble polytetrafluoroethylene plastic (PFA)
PFA has the advantages of both F4 and 46. It has the excellent chemical corrosion resistance and high temperature resistance of F4. Like F46, it can be formed and processed using general thermoplastic processing methods, and is more convenient than F46. PFA is used industrially as anti-corrosion linings and anti-corrosion coatings. Can be used to manufacture pumps, tank linings, bellows, expansion tubes, special hoses, films, etc.
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Fluorine lined valve type
Fluoroplastic lined gate valve
The structure of the flange-connected fluoroplastic-lined gate valve is basically the same as that of conventional general-purpose valves, and it complies with the general technical conditions of general-purpose valves. The difference is that the interior is lined with a layer of fluoroplastic, which is difficult to manufacture. The mold making is more complicated and the production cost is high. high. Therefore, fluoroplastic-lined valves are more expensive than similar general-purpose valves.
The difference is that:
When the gate is opened or closed, there are limit devices and position indicators to prevent damage to the lining material of the valve sealing surface, ensuring the safety of the valve and extending its service life. There is a drain hole in the bottom of the valve or in the valve cover to vent pressure and residue. Fluoroplastic lined gate valve has a straight flow channel with smooth inner wall and small flow resistance coefficient. It is suitable for connecting and cutting off media in petrochemical, food, pharmaceutical and other pipelines.