Suitable for medium temperature -40℃ ~ -196℃ valve is called low temperature valve, and this kind of permanent magnet screw air compressor valve generally adopts long neck valve cover.

The long neck valve cover provides low temperature valves including low temperature emergency cut-off valve, low temperature globe valve, low temperature check valve, SPECIAL low temperature valve for LNG, special low temperature valve for NG, mainly used in 300,000 tons of ethylene, liquefied natural gas and other chemical plants. Output liquid low temperature medium such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products, not only flammable and explosive, and in the heating to gasification, gasification, volume expansion hundreds of times.

The long neck bonnet is required because:

(1) the long neck valve cover has the function of protecting the low temperature valve packing box, because the sealing of the packing box is one of the key to the low temperature valve. Leakage at the stuffing box will reduce the cooling effect and lead to the gasification of liquefied gas. At low temperature, with the decrease of temperature, the elasticity of packing gradually disappears, and the leakproof performance decreases accordingly. Due to the media leakage, the packing and valve stem are frozen, which affects the normal operation of the valve stem and scratches the slurry packing due to the movement of the valve stem up and down, causing serious leakage. Therefore, it is necessary to ensure that the temperature of the standard part of the packing is above 8℃.

(2) The structure of the long-neck valve cover is easy to wrap the cooling material to prevent the cold energy loss of the low-temperature valve.

(3) Low-temperature valve long neck structure is convenient for quick replacement of valve main parts by removing the valve cover. As the process piping and valves in the cold section of the equipment are often installed in the 'cold box', the long-neck bonnet can be extended through the 'cold box' wall. When replacing valve main parts, simply remove the cover without removing the body. Valve body and pipeline welded into one, as much as possible to reduce the leakage of cold box, to ensure the sealing of the valve.

Source: General machinery - air compressor network

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