What is the difference between a globe valve and a cryogenic valve?
Cryogenic valves are valves that can work in deep cold and low temperature conditions. Stop valves are a type of valve. Cryogenic valves include cryogenic stop valves. There are obvious differences between the two in terms of concept, structure, performance, and application scenarios. The following is a detailed introduction:
1. Conceptual differences
(1) Globe valve: Also known as a gate valve, it is a forced sealing valve that "stops" (blocks) the flow of the medium through the vertical movement of the valve disc. Its main function is to cut off or connect the medium in the pipeline.
(2) Cryogenic valve: It is a valve that can work in deep cold and low temperature conditions. Valves with an operating temperature below -40°C are usually called cryogenic valves. They are mainly used in equipment such as gas liquefaction, separation, transportation and storage.
2. Structural differences
(1) Globe valve
Main components: It is mainly composed of valve body, valve cover, valve stem, valve stem nut, valve disc, valve seat, stuffing box, sealing packing, stuffing gland and transmission device.
Movement form: Driven by the valve stem, the valve disc moves up and down along the axis of the valve seat sealing surface, thereby opening or closing the valve.
Sealing characteristics: It is a forced sealing valve. When closing, pressure must be applied to the valve disc to force the sealing surface to prevent leakage.
(2) Cryogenic valves
Special structure: Cryogenic valves usually have a long-necked bonnet structure. The purpose is to keep the valve operating handle and stuffing box structure away from the low temperature area to avoid frostbite of operators. At the same time, it ensures that the stuffing box and the compression sleeve are used at normal temperature to prevent the packing sealing performance from being reduced and extend the service life of the packing. In addition, it may also be equipped with a drip plate structure to prevent low-temperature liquefied water vapor from dripping on the middle flange bolts to prevent bolt rust from affecting online maintenance.
Material requirements: Valve body, bonnet and other pressure-resistant parts usually use tough materials with good low-temperature strength, such as low-temperature carbon steel, 300 series austenitic stainless steel, etc. These materials can still maintain good mechanical properties and low-temperature impact toughness at low temperatures.
3. Performance Difference
(1) Globe valve
Advantages: simple structure, easy to manufacture and maintain; the sealing surface is not easy to wear and scratch, the sealing performance is good, there is no relative sliding between the valve disc and the sealing surface of the valve body when opening and closing, and the service life is long; the valve disc stroke is small when opening and closing, and the height is smaller than that of the gate valve.
Disadvantages: large opening and closing torque, more laborious opening and closing, and longer opening and closing time; large fluid resistance, because the medium channel in the valve body is tortuous, the power consumption is large; poor adjustment performance, generally only suitable for full opening and full closing, not suitable for adjustment and throttling.
(2) Cryogenic Valve
Advantages: can adapt to extremely low temperature environment, can still maintain good sealing performance and mechanical properties at low temperature, ensure the valve reliable operation under low temperature conditions; some cryogenic valves have the characteristics of fast opening and closing, such as cryogenic ball valve, which only needs to rotate 90°from opening to closing, which is conducive to remote operation and emergency shut-off.
Disadvantages: Compared with ordinary valves, the manufacturing process of cryogenic valves is more complicated, requiring the use of special materials and manufacturing processes, and low temperature treatment, etc., so the cost is relatively high.
4. Differences in application scenarios
(1) Globe valve: widely used in various occasions where the medium needs to be cut off or connected, such as in pipeline systems in the chemical, petroleum, electric power, metallurgical and other industries, to control the flow of fluids.
(2) Cryogenic valve: mainly used in ethylene, liquefied natural gas devices, natural gas LPG/LNG storage tanks, receiving bases and satellite stations, air separation equipment, petrochemical tail gas separation equipment, liquid oxygen, liquid nitrogen, liquid argon, carbon dioxide cryogenic storage tanks and tank trucks, pressure swing adsorption oxygen production devices, etc. The output liquid cryogenic media such as ethylene, liquid oxygen, liquid hydrogen, liquefied natural gas, liquefied petroleum products, etc. are not only flammable and explosive, but also gasify when heated, and the volume expands hundreds of times when gasified. The application of cryogenic valves can control the temperature and prevent hidden dangers such as explosion and leakage.