Problems with low-temperature valves
Thread Content
I have previously operated liquid oxygen cryogenic valves, and due to the extremely low temperature of the liquid oxygen, the valves were always covered with a thick layer of snow and ice, making it very difficult to open them. Is there any good solution for this issue? There’s also the issue of the material’s cold brittleness; if not handled properly, it can cause the valve stem to break, which is quite troublesome. I was wondering if there are any good materials available……
Strict manufacturing processes are established for the low-temperature valves produced, specialized equipment is used, and rigorous quality control is applied to the processing of the components. Through a special low-temperature treatment, the roughly processed parts are placed in a cooling medium for several hours (2–6 hours) to relieve stress, ensure the material’s performance at low temperatures, and maintain precise dimensions. This prevents leakage caused by deformation due to temperature changes when the valve is operating in low-temperature conditions. The assembly of valves also differs from that of ordinary valves; the components must be thoroughly cleaned to remove any oil residues in order to ensure proper performance. The main components of the low-temperature valve are subjected to low-temperature treatment, and samples from each batch are tested for low-temperature impact resistance, to ensure that the valve does not become brittle under low-temperature conditions and can withstand the impact of low-temperature media. The following test is performed on each valve: room temperature shell strength test ； Sealing test at normal temperature and low pressure ； Normal temperature and low pressure sealing test ； Low-temperature airtightness test with upper seal (when an upper seal is present) ； Low-temperature gas seal tests, etc., are carried out to ensure that the entire low-temperature valve meets the standards. Valve materials: LCB, LC3, CF8; operating temperatures: -46°C, -196°C. The fracture of the valve stem may be caused by the lack of low-temperature treatment and impact testing for the stem, which failed to eliminate residual stresses.
It is normal for ice to form on low-temperature valves; there is no need to worry about the valve stem breaking. Low-temperature valves are made of materials resistant to low temperatures, and breakage would only occur due to material or design issues
Connect to the air tube, blow hard on this valve!
You may take a look at the two standards, JB/T 7749-95 \"Technical Requirements for Low-Temperature Valves\" and JB/T 7248-94 \"Technical Requirements for Low-Temperature Steel Castings for Valves\". The national standard GB/T 24925-2010 \"Technical Requirements for Low-Temperature Valves\" will come into effect on December 31, 2010.
The thickness of the frost on the valve surface has no relation to the ease with which the valve can be opened. The stem of low-temperature valves used in liquid oxygen environments is usually made of CF3CF8 material; after cryogenic treatment, there is no need to worry about cold-induced brittle fracture
The physical property of thermal expansion and contraction is also evident in metals, especially in low-temperature ball valves. When the temperature drops to -196 degrees, the entire valve body, the seat, and the steel balls all contract, resulting in a several-fold increase in torque. Therefore, the valve stem must be made of CF8M stainless steel or a material with higher strength
The liquid oxygen valve definitely requires an extended valve stem, as well as proper material selection.