Function of DQ961F-25P cryogenic ball valve long neck bonnet
Time: 2021-02-05 20:22:41 Source: Yonglong Valve Reading: zero second
Function of DQ961F-25P cryogenic ball valve long neck bonnet
Low temperature valve is a kind of valve that works in low temperature medium. The valve that is suitable for medium temperature of - 40 ℃~- 196 ℃ is called low temperature valve, and this type of valve generally adopts long neck valve cover. Therefore, the design, manufacture and inspection of cryogenic valves are quite different from those of general valves. In general, according to the operating conditions of cryogenic valves, the following requirements are proposed for the design work:
1) The valve and its assembly shall be able to work for a long time under low temperature medium and ambient temperature (generally 10 years or 3500~5000 cycles);
2) The valve should not be a significant heat source relative to the low-temperature medium, because the heat inflow will reduce the thermal efficiency, and too much heat inflow may also cause the low-temperature medium inside the valve to vaporize, resulting in abnormal pressure rise, causing danger;
3) Low temperature medium shall not have harmful effects on the operating performance of hand wheel and the sealing performance of packing;
4) The structure of the valve assembly in direct contact with low-temperature medium shall meet relevant explosion-proof and fireproof requirements;
5) The valve assembly working at low temperature cannot be lubricated, so measures shall be taken to prevent friction parts from being scratched.
The above requirements shall run through the design process of cryogenic valves. In addition, it should be noted that the above requirements are unique to cryogenic valves, and the design process of cryogenic valves should also comply with the requirements of relevant general valves.
Shanghai Yonglong Valve Factory adopts long neck bonnet to specify low-temperature valves, including low-temperature emergency shut-off valve, DJ41F-40P low-temperature stop valve DQ961F-25P Low temperature ball valves, etc., are mainly used in 300000 tons of ethylene, liquefied natural gas and other chemical plants. The exported liquid cryogenic media, such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, and liquefied petroleum products, are not only combustible and explosive, but also need to be gasified when heating up. When gasifying, the volume expands hundreds of times.
According to the liquefaction temperature of various gases under normal pressure, there are six temperature classes abroad.
The first level is 0~- 46 ℃; Level II: - 47~- 60 ℃; Grade III: - 61~- 70 ℃; Level IV: - 70~- 101 ℃; Class V is - 102~- 196 ℃; Level VI is below - 253 ℃, generally - 46~- 150 ℃ is called low temperature, and below - 150 ℃ is called ultra-low temperature.
Low temperature ball valve | Low temperature stop valve uses long neck bonnet because:
1) The long neck valve cover has the function of protecting the stuffing box of the cryogenic valve, because the tightness of the stuffing box is one of the keys of the cryogenic valve. If the stuffing box leaks, the cold insulation effect will be reduced, leading to the gasification of liquefied gas. In the low temperature state, with the decrease of temperature, the elasticity of the packing gradually disappears, and the leak proof performance decreases. Due to the medium leakage, the packing and the valve stem are frozen, which affects the normal operation of the valve stem. At the same time, the packing will be scratched due to the up and down movement of the valve stem, causing serious leakage. Therefore, ensure that the temperature of the standard part of the filler is above 8 ℃.
2) The structure of the long neck valve cover is convenient for winding cold insulation materials to prevent cold energy loss of low-temperature valves.
3) The long neck structure of the cryogenic valve is convenient for quick replacement of the main parts of the valve by removing the valve cover. Since the process pipes and valves in the cold section of the equipment are often installed in the cold box, the long neck valve cover can protrude through the wall of the cold box. When replacing the main parts of the valve, it is only necessary to remove and replace them through the valve cover instead of removing the valve body. The valve body and the pipeline are welded together to minimize the leakage of the cold box and ensure the tightness of the valve.
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