Why Cryogenic Valves Have Long Stem

Home Why Cryogenic Valves Have Long Stem
03/08/2022
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Valves are of many types and each one has its special characteristic features. Cryogenic valves are one such type of industrial valve that are employed in low-temperature environments. These valves are specifically designed to ensure extreme temperatures and pressures so that they do not malfunction.

An oil and gas industry
Source: Pexels

At the first look, a person will find the cryogenic valves have a long bonnet (or stem) – certainly longer compared to that of the usual industrial valves. Why is it so? Well, this article will explain why cryogenic valves have long stem and how it helps to accomplish their function.

What are Cryogenic Valves?

Valves that are designed to be used in extremely cold temperatures are called cryogenic valves. These valves are specifically made to carry low-temperature fluids like liquid oxygen, nitrogen, hydrogen, liquified natural gas, etc… Pipelines that carry such low-temperature fluids feature cryogenic valves to control the flow.

Cryogenic valves are not just designed to handle low-temperature fluids but also high-pressure gasses and liquids. These valves are widely employed in the oil and gas, petrochemical, and food processing industries among others. 

A cryogenic gate valve
Source: Pinterest

Usually, cryogenic valves are designed to carry and store fluids that have pressure as high as 52 bar and temperature as low as -196℃. It becomes crucial to take several necessary steps while handling cryogenic fluids, as many of them can cause fatal accidents when the pressure and temperature conditions change. This is why cryogenic valves are manufactured with utmost attention – a small fault in these valves can cause irreparable damage.

Common Features of Cryogenic Valves

  • They are lightweight –  helps them to carry low-temperature fluids efficiently.
  • Cryogenic valves are usually built with low conductivity.
  • These valves are built to fit into tight spaces. 
  • Cryogenic valves are assembled in a clean room that is free of lubricants. This is because even the slightest trace of unwanted material can pose a great threat at cryogenic temperatures.

Types of Cryogenic Valves

Not all industrial valves are suitable for cryogenic purposes – some valves are not right to be designed into cryogenic valves because they lack certain features. Some of the commonly found industrial cryogenic valves are ball, butterfly, gate, and globe valves.

  • Cryogenic Ball Valves – One of the most common options for cryogenic purposes, these valves are the best option for tight shut-off properties. Although they experience wear and tear easily, these valves must be used in places that have unrestricted flow.
  • Cryogenic Butterfly Valves – Short in length and easy to operate, cryogenic butterfly valves make a great choice for applications that require frequent quick open and close actions.
  • Cryogenic Globe Valves – A linear motion valve with an internal disc, a cryogenic valve can offer long-time effective sealing properties. But despite being durable, they are not recommended for high-flow areas.
A Cryogenic Globe Valve
Source: DomBor
  • Cryogenic Relief Valves –  These valves are designed to prevent damage that is caused by the expansion of the fluids inside pipelines. When the pressure of the fluid crosses the safety limit, the valve allows steam to escape – this will maintain the pressure situation. 
  • Cryogenic Gate Valves – Like all other cryogenic valves, the gate valve also features an extended bonnet. Even in the fully-open position, the valve creates a minimal pressure drop.

Working Principle of Cryogenic Valves

It has been established that the material from which a cryogenic valve is made plays a crucial role in the performance of the valve. This is because valves designed to operate in normal conditions will not be useful in extremely low temperatures – the metal will become brittle. Also, normal valves will compromise the sealing quality in a cryogenic situation.

A cryogenic valve is generally set to the fully-closed position in a pipeline – this is done to ensure that cryogenic fluids are restricted from flow or evaporation. In case of an increase in pressure, the valve opens to let the fluid flow. This will lower the pressure and avert any possible problems of vaporization. Once the pressure reaches the desired amount, the valve shuts off quickly with a bubble-tight shutoff. By doing so, leakage is prevented.

The structure of a cryogenic valve needs to be thoroughly studied if one wishes to understand its working. One of the defining features of a cryogenic valve that differentiates it from normal industrial valves is its extended stem. Many do not know why cryogenic valves have long stem, but to know how a cryogenic valve functions, it is crucial to understand this.

The Reason Why Cryogenic Valves Have Long Stem

A Cryogenic Relief Valve with a Long Stem
Source: DomBor

Many fluids carried by cryogenic pipes and valves are flammable or explosive, or both. Also, the fluids may expand a hundred times their actual size when the temperature increases. This means that even a minor leakage or spillage can cause disastrous results. To ensure safe transmission, the fluids must be maintained at the right temperature and pressure.

This is where the extended bonnet (or stem) of a cryogenic valve comes to the rescue. The long stem of a cryogenic valve cannot be spotted in a normal industrial valve because it serves a special function in low-temperature situations. There are 3 main reasons why cryogenic valves have long stem:

  1. The extended stem ensures that the packing of the valve is warm. In low-temperature situations, the stuffing box will be affected, which leads to freezing between the packing and stem, thus resulting in leaking. When the packing leaks, the low-temperature state is broken, and the fluids evaporate. To avoid all these issues, the long stem is designed to keep the stuffing box above 8℃.
  2. As the stem is extended, it gives a lot of space to wrap jacketing materials that prevent the loss of cold energy. By sustaining the cold temperature, the fluids inside the valve and the pipeline are maintained in their original state.
  3. The long bonnet of a cryogenic valve helps in the easy positioning of cryogenic valves even in restrictive spaces. The valves and pipes used in such situations are installed in a “cold box” and the long stem can fit in the wall of the box.

Cryogenic Valves Applications

Cryogenic valves are used in several industries because of their crucial functioning. Some of the common sectors where cryogenic valves applications can be found include oil and gas, petrochemical, chemical, food processing, and air separation industries.

  • LNG Plants and Terminals – Liquefied Natural Gas (LNG) is transported easily by using cryogenic pipelines and valves – as the gasses have the risk of expanding, they need to be handled with caution.
  • Food and Beverage Industry – Cryogenic valves are commonly found in the food and beverages industry because they are suitable for carrying cold fluids. Also, these valves are employed in freezers.
Huge storage units in a factory
Source: Unsplash
  • Chemical and Petrochemical Industry – As for the chemical industry, there are several products like ethylene, liquid oxygen, and liquid nitrogen that need to be handled at extremely low temperatures. For this purpose, cryogenic valves are a perfect choice. They are also very useful in carrying LPG and other fluids.
  • Medical Industry – The scope of cryogenic valves in the medical industry is high – they are used for the storage of essential gasses like liquid oxygen.

Conclusion

Cryogenic valves have unique functions as well as features – these valves find applications in a wide range of industries because of the same reasons. Without knowing things like why cryogenic valves have long stem, one cannot choose the right type of valve for any purpose. Understanding the types of cryogenic valves and their working will help a buyer make an informed decision.

If you are looking for a reliable cryogenic valve manufacturer, then DomBor is the perfect choice for you. As a leading manufacturer of industrial valves, we specialize in all types of industrial valves and provide custom solutions. Get in touch with us today and pick the suitable valve solutions for your projects.

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