As we all know, the valve works for medium at temperature -40 ℃ ~ -196 ℃ is called ‘cryogenic valve’.

Cryogenic valves, including cryogenic emergency shut valve, cryogenic ball valve, cryogenic gate valve, LNG cryogenic valve, NG cryogenic valve, are usually found in chemical plants such as ‘300,000 tons of ethylene’ project and production of liquefied natural gas.

Ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum, and other liquid media the cryogenic valve transfers are flammable and explosive. What is more, they are going to gasify and expand hundreds of times when the temperature rises.

This kind of valve is always equipped with an extended bonnet or namely extended stem. That’s because:

1. The extended bonnet can prevent the stuffing box, which plays an important role in the cryogenic valve and other valves, from the damage of low temperature.

As the temperature goes down, the packing will gradually become less elastic and lost its ability to prevent leakage. Then, medium freeze in the space between the packing and the stem, hampering the movement of the stem and scratching the packing as the stem moves. In the end, what follows is severe leakage.

Therefore，a extended stem is used to ensure that the packing is warm enough, at least above 8 ℃.

2. The extended structure of bonnet makes it convenient to wrap special materials around the valve, preventing the loss of cold energy.

3. The pipes and valves are often installed in the so-called 'cold box', but its ‘long neck’ can go through the wall of the 'cold box'. Based on that, The extended stem makes it convenient to dismantle or replace the main parts of the valve quickly through the bonnet.

Hence，the valve body and the pipeline are welded together to reduce the leakage of the cold box as much as possible and ensure the sealing performance of the valve.