What are Cryogenic Valves?
What are Cryogenic Valves?
As their name implies, cryogenic valves are engineered for extremely cold environments. They are primarily utilized by industries dealing with Liquefied Natural Gas (LNG) or Compressed Natural Gas (CNG). The oil and gas sector commonly operates in cryogenic temperature ranges starting at -150°C (-238°F). Some gases are termed 'cryogenic' not because of their temperature but because of the complex process needed to compress their volume. Cryogenic valves facilitate the safe and efficient transport and storage of such gases.
Cryogenic valves are designed to store gases safely and are also highly efficient during transportation, capable of operating in pressures up to 52 bar (750 psi) and temperatures as low as -196°C (-320°F).
Working Mechanism of Cryogenic Valves
Cryogenic valves are naturally kept in a closed position to ensure the security and containment of cryogenic gases or other media. The valve reacts to high pressure by opening to allow the gas or other media to flow through effortlessly. This flow persists until the pressure decreases, prompting the valve to close with a specialized metal seat for bubble-tight shutoff to prevent leaks.
Why Are Other Valves Not Suitable?
Cryogenic gases are highly sensitive, and any unwanted leaks can lead to significant, costly damage. Converting standard-temperature gases into cryogen is an expensive process. Standard valves fail in extreme temperatures because they expand and contract at different rates, causing seal breaks and unintentional leaks. These temperature fluctuations have long posed challenges for the storage, transport, and study of cryogenic gas processing.
Why Do Cryogenic Valves Have an Extended Bonnet?
Cryogenic valves, used for transferring flammable and explosive liquids like ethylene, liquid oxygen, liquid hydrogen, LNG, and liquefied petroleum, are equipped with an extended bonnet or stem. Here’s why:
- The extended bonnet shields the stuffing box from low-temperature damage. As temperatures drop, the packing loses its elasticity and ability to prevent leaks, which can lead to severe leakage. An extended stem ensures the packing remains warm enough, ideally above 8°C.
- The extended bonnet structure allows for wrapping special materials around the valve, preventing the loss of cold energy.
- Valves installed in 'cold boxes' feature a 'long neck' that protrudes through the box wall, facilitating the quick dismantling or replacement of valve parts.
Consequently, the valve body and pipeline are welded to minimize leaks and ensure optimal sealing performance.
Types and Differences of Cryogenic Valves
Various shapes and sizes of cryogenic valves are available today, suitable for different pressure ranges. Common types include Ball, Butterfly, Gate, Globe, Check, and Relief valves. They can be either manual or automatic, essential for large systems.
Cryogenic ball valves feature a polytetrafluoroethylene body, offering better flow rates than globe valves. They are highly effective for ensuring tight seals but can wear easily around the seals and the ball, making them suitable for systems with unobstructed flow paths.
Cryogenic butterfly valves have a central circular disc, making them shorter in length. They are lightweight, cost-effective, easy to operate, and ideal for systems requiring quick opening and closing actions.
Cryogenic gate valves feature a wedge-shaped gate that closes in line with the body mounting, resulting in minimal pressure drop even when fully open.
Cryogenic globe valves have a spherical shape with an internal disc that rotates at a 90-degree angle to its body mounting, providing long-term effective sealing. However, they are not recommended for high-flow systems.
Cryogenic relief valves prevent overpressure by allowing steam to escape if safety limits are exceeded, while cryogenic check valves maintain pressure and prevent fluid backflow.
Remarks of the Author
Cavity Relief Ball Valve
Years ago, while working for Shell, I first encountered a Cavity relief ball valve in cryogenic service. What is it?
SHELL MESC specifies a pressure equalizing hole of at least 3 mm in the ball and mandates that the ball valve must have an automatic overpressure relief mechanism, as per Cryogenic standard BS 6364.
Another solution is using self-venting ball seats per EEMUA 182 specifications, where surplus pressure escapes around the ball seat.
Always remember that cryogenic gases are very sensitive, and leaks can pose significant risks. Thus, cryogenic valves are essential for ensuring the proper functioning of such systems.
Reference(s) for this page:
www.dvsvalve.com
www.evergreenmidwest.com
valveman.com
www.cam-spa.it
Types of Valves in Cryogenic Applications
High-pressure applications require cryogenic valves to deliver efficient sealing according to stringent testing requirements. These valves are carefully engineered and tested with all safety precautions in mind, ensuring reliability.
Choose the best cryogenic valves from vendors who can meet your needs and expectations. Over the past 20 years, Dombor, a leading cryogenic valve manufacturer, has supplied valves to various industries. Contact Dombor now to discuss your requirements and find the best cryogenic solution. Achieving a balance between quality and affordability is crucial, and industrial valve manufacturer Dombor can help meet your business needs.
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