Valves Below Zero
The high temperature extremes that occur in some processes or operations and the tolerance of certain metals to such heat tend to earn a lot of attention and respect. It’s got to be scorching hot before 316 stainless steel will melt (2507°F – 2552°F in case you were wondering).
At the other end of the spectrum, cold temperatures can wreak havoc on valves and fittings, too. The elastomers that comprise soft goods such as O-rings and discs may become brittle under frigid temperatures. The resulting inflexibility compromises the valve’s ability to seal.
Low temperatures should not be confused with cryogenic temperatures. Cryogenic environments range from a high temperature of -238°F (-150°C) to a low of -460°F (-273°C), also known as absolute zero.
When we talk about low temperatures in this article, we refer to the range between 32°F (0°C) and the low end of the ambient temperature scale – temperatures like one might find in northern regions of North America, Siberia, the Arctic and Antarctic. We are not referring to cryogenic temperatures.
Operations such as some oil and gas refining processes may take place in climates where the cold is unavoidable. Temperatures not only reach below freezing, but they can remain there for weeks on end. Standard valve models are rated for use down to 32°F.
Often times machinery and equipment in such locations is unattended and in remote areas where damaged valves and equipment are harder to get to for repairs.
What to Look For When Choosing Low-Temperature Valves
Selection of trim materials that will withstand low temperatures is crucial for reducing the risk of cold-related valve failure and/or malfunction. Two factors that affect the material’s cold tolerance are resiliency and periods of dormancy.
Resiliency – the ability of an item to return to its original shape after being stretched is known as resiliency. Resiliency declines as the temperature decreases. Under these conditions the valve’s disc, made of elastic polymers (a/k/a elastomers), will become hard or brittle, reducing its ability to form a proper seal and allowing for leakage. These elastomers also shrink under decreasing temperatures, further compromising the integrity of the seal.
Dormancy – in cases where a valve is not operated for long periods of time, such as when the cycling is long, the O-ring or seal may be in contact with the body for days or weeks. Long-term contact such as this can cause the seal to stick to the metal surfaces, no doubt affecting the valve’s performance.
The chart shown below shows the O-Ring and stem seal materials available from CPV Manufacturing and their corresponding temperature range. The standard, Viton, extends as low as -15°F (-26°C). Ethylene propylene (EPDM) ranges as low as -70°F (-57°C).
Low-Temperature Seal Materials
|O-Ring & Stem Seal Temperature Ratings
|Buna-N (Nitrile NBR)
|-30°F to +250°F (-34°C to 121°C)
|-15°F to +400°F (-26°C to 205°C)
|EPDM (Ethylene Propylene)
|-70°F to +250°F (-57°C to 121°C)
|-40°F to +180°F (-40°C to 82°C)
It’s not only the trim materials that are subject to compromise in cold temperatures. The metal body has to be able to withstand the cold as well. Cast iron and some carbon steel alloys are not suited for cold temperatures beyond a certain range.
Depending on the manufacturer, additional testing may be done to ensure quality and safety. Valves should always be tested to ensure that they meet at least the minimum safety and quality standards. These tests will include endurance, seat leakage, and external leakage. Always refer to industry regulations for required standards.
Manufacturers offering valves encompassing a lower temperature range do so using the newest technologies in valve manufacturing. Very few manufacturers offer these cold-temperature options.
You can trust that valves and fittings produced by CPV Manufacturing, with optional seal materials approved for temperatures as low as -70°F, are the highest quality and have met or exceeded all safety and quality standards.
Low-temperature valves and fittings are not available from all manufacturers. In order to simplify inventory and ordering, and to ensure that worldwide industry standards and regulations are met, companies may choose to stick with one source and possibly one specific material for all their valves or for a particular application. They may use the same valves across the board, regardless of location and temperature.
When low-temperature valves and fittings are needed, be sure to consider the reliability of the materials as well as the reliability and reputation of the manufacturer. You want to be able to get the valves and fittings that you need quickly. It’s equally important to have access to customer support.
Questions about CPV’s low-temperature or other valves? Contact us.