1. A cryogenic valve body should be able to withstand the expansion and contraction caused by temperature changes, and the structure of the valve seat will not be permanently deformed by temperature changes.
2. Low temperature valve cover: long neck valve cover structure, the purpose is to protect the stuffing box. The long neck cover structure is also easy to wind cold retaining materials.
3. Low temperature valve disc (gate plate) : The gate valve adopts flexible or open gate plate; Globe valve flat seat and needle valve, using plug disc. These structures maintain a reliable seal regardless of temperature changes. 4) Valve stem: the valve stem should be plated with chromium, nickel and phosphorus or nitride treatment, in order to improve the hardness of the stem surface, prevent the stem and packing, packing pressure sleeve bite each other, damage the sealing packing, causing packing box leakage.
5. Low temperature valve gasket: the selection of gasket should consider the low temperature properties of the material, such as compression and resilience, pretightening force, fastening pressure distribution and stress relaxation characteristics.
6 packing box and packing: packing box can not contact with the low temperature section directly, and set in the top of the long neck valve cover, so that the packing box is far away from the low temperature zone, working in the temperature environment above 0℃, improve the sealing effect of packing box. The packing box mostly adopts a two-stage packing structure with an intermediate metal isolation ring. Grease can be added from the middle of the packing box to form an oil seal layer and reduce the pressure difference of the packing box.
7. Upper seal: the low temperature valve is equipped with upper seal structure, the upper seal should be surfacing cobalt chromium tungsten carbide, finishing grinding.
8. Low temperature valve seat, valve disc, (gate) sealing surface: the closed parts of low temperature valve adopt cobalt-chromium tungsten carbide surfacing mechanism. Soft seal structure due to PTFE expansion coefficient is large, brittle at low temperature, so only use temperature higher than -70℃ low temperature valve, but polytrifluoride can be used for -162℃ low temperature valve.
9. Middle flange bolt:
1) : Bolts should have enough strength, because bolts often break due to fatigue when working under repeated loads.
2) : Because the bolt is easy to cause stress concentration at the root of the thread, it is better to use the bolt with full thread structure.
10. Cold protection: also known as temperature insulation plate, is a circular plate welded under the stuffing box long neck part. Improve the heat preservation
The effect.
11. Measures to prevent abnormal pressure boost: after the valve is closed, some liquid will remain in the valve chamber. Over time, these liquids absorb heat from the atmosphere, rise back to normal temperature and re-vaporize. After gasification, its volume expands dramatically, increasing by about 600 times as much, resulting in extremely high pressure, and used inside the valve body. This phenomenon is called abnormal boost, is a cryogenic valve unique phenomenon. An abnormal boost will force the gate against the seat, causing the gate to fail to open. High pressure will flush out the middle flange gasket or damage the packing; Can also cause body, valve cover deformation, so that the valve seat sealing performance significantly decreased. In order to prevent abnormal boost phenomenon, the general low temperature valve in the structure of the following measures:
1) Set pressure relief hole, also known as pressure balance hole or vent hole.
2) Set a lead pipe or install a safety valve on the valve to discharge the abnormal high pressure.

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