Advantages and disadvantages of various valves:
1. Gate valve: A gate valve refers to a valve whose closing element (gate) moves vertically along the channel axis. It is mainly used to cut off the medium in pipelines, that is, fully open or fully closed. Generally, gate valves cannot be used to regulate flow. It can be applied to both low temperature and high temperature and high pressure, and can be made of different materials according to the valve. But gate valves are generally not used in pipelines for transporting mud and other media.
Advantages: ① Low fluid resistance; ② The required torque for opening and closing is relatively small; ③ It can be used on ring network pipelines where the medium flows in both directions, which means that the flow direction of the medium is not restricted; ④ When fully open, the sealing surface is less eroded by the working medium than the shut-off valve; ⑤ The physical structure is relatively simple and the manufacturing process is good; ⑥ The structural length is relatively short.
Disadvantages: ① The external dimensions and opening height are relatively large, requiring a large installation space; ② During the opening and closing process, the sealing surface is subject to relative friction, resulting in significant wear and even causing abrasions at high temperatures Generally, gate valves have two sealing surfaces, which adds some difficulties to processing, grinding, and maintenance; ④ Long opening and closing time.
2. Butterfly valve: A butterfly valve is a type of valve that uses a disc type opening and closing element to rotate back and forth about 90 degrees to open, close, and regulate fluid channels.
Advantages: ① Simple structure, small size, light weight, and low consumables, not suitable for large diameter valves; ② Quick opening and closing, low flow resistance; ③ Can be used for media with suspended solid particles, and can also be used for powder and granular media depending on the strength of the sealing surface. Suitable for bidirectional opening, closing, and adjustment of ventilation and dust removal pipelines, widely used in gas pipelines and waterways in metallurgy, light industry, power, and petrochemical systems.
Disadvantages: ① The flow regulation range is not large, and when it reaches 30%, the flow will increase by more than 95%; ② Due to the limitations of the structure and sealing materials of butterfly valves, they are not suitable for use in high-temperature and high-pressure pipeline systems. The general working temperature is below 300 ℃ and PN40; ③ The sealing performance is relatively poor compared to ball valves and globe valves, so it is used in places where sealing requirements are not very high.
3. Ball valve: evolved from a plug valve, its opening and closing component is a sphere that rotates 90 ° around the axis of the valve stem to achieve the purpose of opening and closing. Ball valves are mainly used on pipelines to cut off, distribute, and change the direction of medium flow. Ball valves designed with V-shaped openings also have good flow regulation functions.
Advantages: ① Low flow resistance (actually 0); ② Because it does not get stuck during work (in the absence of lubricants), it can be reliably applied to corrosive media and low boiling point liquids; ③ Complete sealing can be achieved within a large range of pressure and temperature; ④ It can achieve fast opening and closing, with some structures having an opening and closing time of only 0.05~0.1 seconds, to ensure that it can be used in the automation system of the test bench. When quickly opening and closing the valve, there is no impact during operation; ⑤ The spherical closure component can automatically locate at the boundary position; ⑥ The working medium is reliably sealed on both sides; ⑦ When fully open and fully closed, the sealing surfaces of the ball and valve seat are isolated from the medium, so the medium passing through the valve at high speed will not cause erosion of the sealing surface; ⑧ Compact structure and light weight make it a reasonable valve structure for low-temperature medium systems The valve body is symmetrical, especially the welded valve body structure, which can well withstand the stress from the pipeline; ⑩ The closure component can withstand the high pressure difference during closure The ball valve with a fully welded valve body can be directly buried underground, preventing the valve components from being corroded. Its high service life can reach 30 years, making it an ideal valve for oil and gas pipelines.
Disadvantages: ① Because the main valve seat sealing ring material of ball valves is polytetrafluoroethylene, it is inert to almost all chemicals and has comprehensive characteristics such as low friction coefficient, stable performance, low aging, wide temperature applicability, and excellent sealing performance. However, the physical properties of polytetrafluoroethylene, including its high coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require the design of valve seat seals to revolve around these characteristics. So, when the sealing material becomes hard, the reliability of the seal is compromised. Moreover, polytetrafluoroethylene has a lower temperature resistance rating and can only be used below 180 ℃. Beyond this temperature, the sealing material will age. When considering long-term use, it is generally not used at 120 ℃ Its regulating performance is relatively poor compared to globe valves, especially pneumatic valves (or electric valves).
4. Globe valve: refers to a valve in which the closing element (valve disc) moves along the centerline of the valve seat. According to the movement of the valve disc, the change in the valve seat opening is directly proportional to the stroke of the valve disc. Due to the relatively short opening or closing stroke of the valve stem and its highly reliable shut-off function, as well as the proportional relationship between the change in the valve seat opening and the stroke of the valve disc, this type of valve is very suitable for regulating flow. Therefore, this type of valve is very suitable for cutting off, regulating, and throttling purposes.
Advantages: ① During the opening and closing process, the friction between the valve disc and the sealing surface of the valve body is smaller than that of a gate valve, making it wear-resistant. ② The opening height is generally only 1/4 of the valve seat channel, so it is much smaller than gate valves; ③ Usually, there is only one sealing surface on the valve body and disc, so the manufacturing process is relatively good and easy to maintain; ④ Due to the fact that its filler is generally a mixture of asbestos and graphite, its temperature resistance level is relatively high. Generally, steam valves use globe valves.
Disadvantages: ① Due to the change in the flow direction of the medium through the valve, the small flow resistance of the globe valve is also higher than most other types of valves; ② Due to the longer travel, the opening speed is slower than that of a ball valve.
5. Plug valve: refers to a rotary valve with a plunger shaped closure, which opens or closes by rotating 90 ° to connect or separate the channel port on the valve plug with the channel port on the valve body. The shape of the valve plug can be cylindrical or conical. Its principle is basically similar to that of ball valves. Ball valves are developed on the basis of plug valves and are mainly used in oil field exploitation, as well as in the petrochemical industry.
6. Safety valve: refers to an overpressure protection device used on pressurized vessels, equipment, or pipelines. When the pressure inside the equipment, container or pipeline exceeds the allowable value, the valve will automatically open and then discharge the full amount to prevent the equipment, container or pipeline and pressure from continuing to rise; When the pressure drops to the specified value, the valve should automatically and promptly close to protect the safe operation of equipment, containers, or pipelines.
7. Steam trap: In the transportation of steam, compressed air and other media, some condensed water may form. In order to ensure the efficiency and safe operation of the device, these useless and harmful media should be discharged in a timely manner to ensure the consumption and use of the device. It has the following functions: ① It can quickly eliminate the generated condensed water; ② Prevent steam leakage; ③ Exclude air and other non condensable gases.
8. Pressure reducing valve: It is a valve that reduces the inlet pressure to a desired outlet pressure through regulation, and relies on the energy of the medium itself to automatically maintain a stable outlet pressure.
9. Check valve: also known as reverse flow valve, check valve, back pressure valve, and one-way valve. These valves are automatically opened and closed by the force generated by the flow of the medium itself in the pipeline, and belong to a type of automatic valve. Check valves are used in pipeline systems to prevent medium backflow, pump and drive motor reversal, and release of container media. Check valves can also be used on pipelines to supply auxiliary systems where the pressure may rise above the system pressure. They can be mainly divided into swing type (rotating according to the center of gravity) and lift type (moving along the axis).