Cryogenic valve is a kind of valve working in low temperature medium. With the continuous expansion of the production scale of cryogenic engineering products, liquid oxygen, liquid nitrogen, liquid ammonia and liquefied petroleum gas are widely used. A large number of cryogenic valves are required for the liquefaction, fractionation, transportation and storage of the above substances
1.The temperature class of cryogenic valve
According to the liquefaction temperature of various gases under atmospheric pressure, it is generally divided into six temperature classes.
The first class is 0 ~ – 46 ℃
the second class is – 47 ~ – 60 ℃
the third class is – 61 ~ – 70 ℃
the fourth class is – 70 ~ – 101 ℃
the fifth class is – 102 ~ – 196 ℃
the sixth class is below – 253 ℃
2.General design requirements for cryogenic valves
The working conditions of cryogenic valve are harsh. Most of its working medium is flammable, explosive and highly permeable. The lowest working temperature can reach – 269 ℃, and the maximum working pressure can reach 10MPa. Generally, according to the service conditions of cryogenic valves, the following requirements are put forward for the design work:
1. The valve and spare parts shall be able to work for a long time under low temperature medium and ambient temperature (generally 10 years or 3500 ~ 5000 cycles)
2. Compared with the low temperature medium, the valve should not be a significant heat source, because the inflow of heat will reduce the thermal efficiency, and if the heat inflow is too much, the low-temperature medium inside the valve may vaporize, causing abnormal pressure rise and causing danger
3. Low temperature medium should not have harmful effect on the operation performance of handwheel and sealing performance of packing
4. The structure of valve assembly in direct contact with low temperature medium shall meet relevant explosion-proof and fire-proof requirements
5. The valve assembly working at low temperature cannot be lubricated, so measures should be taken to prevent the friction parts from being scratched
Post time: Nov-25-2020