Valves are devices which regulates, directs and controls the flow of fluids like slurries, fluidized solids, gases and liquids. This is done by closing, opening or obstructing partially the various passageways and are technically considered as fittings though normally discussed separately. If the valve is open, the fluid flows to a direction from a higher pressure part to a lower one.
These have many uses like in residential areas where it controls the taps and clothes and dish washers, controlling irrigation water and controlling processes in industrial purposes. Sometimes, you would need to have cryogenic valve modification when the standard ones do not fit your needs. The modifications needed should be able to withstand the very cold temperature of the stored materials.
Cold temperature is not the only factor which determines if the certain gas is considered cryogenic but also the increased pressure used to compress its volume. They should be colder than negative 150 degree Celsius because warmer than this until 37 degree Celsius is already known as refrigeration. These details are what is use for gas and oil industry.
It is important to understand where is the start of cryogenic temperatures when selecting for valves. There will be a number of things should be understood regarding their coldness when considering the ways in choosing one that would work for a longer time. This is because its industry is conservative and specific preparation for cryogenic services is warranted.
Leakage of cryogen does not only pose a danger but is very expensive also, specially when the cost of making the gas into one is considered. Severe variations in temperature could affect the valves due to its components like seats, ball, stem seals, stem, bonnet and body would expand and contract in varying rates. The reason for this is their material composition being different to one another or the time being exposed to oxygen varies.
Environmental heat gains is something you will constantly battle against when you deal with cryogens which necessitates piping and valve insulation. These liquids, such as helium, argon, oxygen and nitrogen, do not want to stay that way and would transform violently into gases when given the chance. You need special consideration to allow pressure buildup in designing the system.
There is no strict guidelines when selecting the valve type for a cryogenic service though the tendency is there to choose quarter turn ball ones for their capabilities to shut it off tightly. For larger sizes, gate variations are utilized often over ball option because the latter is more costly. But the initial cost is the only one expensive and save you more later.
Vales intended for cryogenic services must be assembled inside a clean room without using any lubricant. If lubricants are used, they should be compatible with cold service and must have no foreign material like dirt, grease and machine oil. This might affect its performance and problems may happen.
When buying valves for this purpose, insist in seeing the documented procedure for their cleaning. Verify if the procedures were followed while in the assembly process. This is to ensure their quality and be free from contaminants.