What is a cryogenic ball valve?
Cryogenic ball valve refers to the ball valve that can be used under low temperature conditions. Generally, the ball valve with working temperature lower than – 40 ℃ is called low temperature ball valve. Low temperature ball valve is applicable to the management system of low-temperature liquid storage and transportation equipment. It has the characteristics of flexible switching and reliable sealing. It can also be used in the management system of other low-temperature and cryogenic media. This product is mainly used to export liquid low-temperature media, such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products and other low-temperature media. The low-temperature ball valve is applicable to all kinds of pipelines. It is used to cut off or connect the medium in the pipeline. Different materials are selected, which can be applied to different temperatures and media respectively. The working temperature is – 196 ℃. The driving mode of low-temperature ball valve is manual, worm gear drive, pneumatic or electric. Low temperature ball valves are generally connected by flange or welding.
Design specification for low temperature ball valve
Design standard: API 6D, GB/T 19672, GB/T 12237;
Structure length: API 6D, ASME B16.10, GB/T 12221;
Flange connection standards: ASME B16.5, ASME b16.47, GB/T 9113, JB/T 79, HG/T 20592;
Butt welding connection standard: ASME B16.25, GB/T 12234;
Fire protection requirements: API 6FA, API 607;
Pressure test: API 6D, API 598, GB/T 13927, GB/T 26480.
Product features of low temperature ball valve
1. The structure of setting a pressure reducing hole on the valve core is adopted.
2. The stem height is the appropriate length obtained through calculation and test.
3. The gasket is made of ceramic filler material with stable sealing performance.
4. In order to reduce the heat loss of the valve body, especially to ensure the use of the valve at low temperature, it is specially designed as a valve body with light weight and small size.
5. The long shaft valve is a valve with low-temperature fluid flowing through. It adopts the form of long stem, which can avoid the effect of external heat and keep the gland at room temperature to prevent the performance degradation of the cover seal.
Advantages of low temperature ball valve
1. Low fluid resistance
2. Simple structure, small volume, light weight and easy maintenance.
3. Good sealing performance.
4. It is not limited by the installation direction, and the flow direction of media can be arbitrary.
5. No vibration and low noise.
Disadvantages of low temperature ball valve
1. High processing precision, high cost and difficult to use at high temperature. If there are impurities in the pipeline, it is easy to be blocked by impurities, resulting in the valve unable to open.
2. It cannot be used as throttling.
Structural design and manufacturing characteristics of low temperature ball valve
According to the standard requirements, ball valves with a temperature lower than – 50 ℃ are generally designed with a long neck structure to improve the temperature of the packing and ensure the reliable sealing of the valve stem packing. The neck length is generally designed according to the standard requirements. If the user has special requirements, it can also be designed according to the contract requirements.
For the valve used for low-temperature medium, when the valve is in the closed position, the volume of low-temperature liquid medium retained in the valve cavity will expand sharply due to gasification when the temperature rises, resulting in abnormal rise of the valve cavity, which will seriously cause accidents such as valve rupture. The ball valve has the function of automatic pressure relief in the middle chamber. When the middle chamber is abnormally pressurized, the medium in the middle chamber can automatically relieve the pressure by overcoming the spring preload and pushing the valve seat away from the ball, so as to ensure the safety of the valve.
According to the contract requirements, low temperature test can be carried out to test the operating torque, sealing performance and other indicators of the valve at low temperature.
The parts of the valve are treated at low temperature to ensure the shape and dimensional stability of the parts at low temperature.
Types of low temperature ball valves
Low temperature ball valves are divided into low-temperature floating ball valves and low-temperature fixed ball valves. See the data of floating ball valves and fixed ball valves for their product range, structural length and connecting flange size. For ball valves with a temperature higher than – 50 ℃, the long neck structure design is generally not adopted. For ball valves with a temperature lower than – 50 ℃, the neck length is generally designed according to the standard requirements, or according to the requirements of customers.
Material selection of low temperature ball valve
General steel will appear low-temperature brittleness at low temperature. Therefore, selecting appropriate valve body material according to the minimum working temperature of low-temperature ball valve is a key to design and manufacture. The minimum operating temperature of valve body material is shown in the table below. Low temperature impact test shall be conducted for low-temperature materials according to the standard requirements. For valves with service temperature lower than – 100 ℃, the valve body, bonnet and valve stem shall be subject to cryogenic treatment after rough machining, and the sealing surface of ball and valve seat shall be subject to cryogenic treatment after spray welding/surfacing cemented carbide, and then grinding and assembly to ensure the applicability of materials at low temperature. In addition, fillers, gaskets, bolts and nuts also need to be made of materials suitable for low temperature conditions.
Low temperature ball valve VS low temperature stop valve
In recent years, there are more and more low-temperature ball valves and low-temperature stop valves in the market, but these two low-temperature valves have their own advantages and play different roles under different working conditions. So what’s the difference between the two valves? How to grasp the selection? Next, Yonglong valve will lead you to understand.
Compared with similar low-temperature stop valves, low-temperature ball valves have larger flow diameter. Cryogenic ball valves provide faster opening and closing movements and are suitable for tank applications as well as cryogenic pumps, pipelines or low-pressure trailers. Low temperature ball valves are available in various sizes and operate at temperatures from + 120 ° C to – 196 ° C. Low temperature ball valves are widely used in very low temperature and low temperature applications, including but not limited to LNG, industrial gas, spiritual and steel services, mining, pharmaceutical, sewage, water treatment, carbon dioxide injection/mixing, cooling and oil/gas applications. There are many kinds of low-temperature ball valves, such as electric low-temperature ball valve, pneumatic low-temperature ball valve, long shaft pneumatic low-temperature ball valve, etc.
Low temperature stop valve is only applicable to full opening and full closing, and regulation and throttling are not allowed. The medium flows into the valve chamber from above the valve disc. At this time, under the action of medium pressure, the force to close the valve is small, while the force to open the valve is large, and the diameter of the valve stem can be reduced accordingly. The application scope of low-temperature stop valve includes gas liquefaction, liquid oxygen, liquid hydrocarbon, liquefied natural gas, liquid nitrogen, LNG system, etc.
The opening and closing part of the low-temperature stop valve is a plug-shaped valve disc, the sealing surface is flat or conical, and the valve disc moves in a straight line along the center line of the fluid. The movement forms of the valve rod include lifting rod type (the valve rod is lifted and the handwheel is not lifted), and lifting rotating rod type (the handwheel rotates and lifts with the valve rod, and the nut is set on the valve body). The stop valve is only applicable to full opening and full closing, and regulation and throttling are not allowed. The low temperature stop valve has the advantages of simple structure, convenient manufacture and maintenance, small working stroke, short opening and closing time, good sealing performance, low friction between sealing surfaces and long service life. However, the low-temperature stop valve also has disadvantages, such as large fluid resistance and large force required for opening and closing, which is not suitable for media with particles, high viscosity and easy coking; Poor regulation performance.
The low temperature ball valve is mainly characterized by compact structure, reliable sealing, simple structure and convenient maintenance. The sealing surface and spherical surface are often closed, which is not easy to be eroded by media and easy to operate and maintain. It is suitable for general working media such as water, solvent, acid and natural gas, as well as media with poor working conditions, such as oxygen, hydrogen peroxide, methane and ethylene, It is widely used in various industries. The valve body of low-temperature ball valve can be integral or combined. The advantages include small fluid resistance and basically no flow resistance for full-diameter ball valves; Simple structure, small volume and light weight; It is convenient to operate and open and close quickly. It can be controlled from full open to full close by 90 ° and convenient for remote control; Wide range of application, diameter from small to several millimeters, up to several meters, from high vacuum to high pressure; High machining precision and high cost.
China Cryogenic Ball Valves Manufacturer www.sfutube.com supplies Low temperature floating ball valve and low temperature fixed ball valve for industrial use, in kinds of materials such as carbon steel, stainless steel, alloy steel, etc.