Because steam is generally a high-temperature medium, butterfly valves and ball valves are not suitable, and diaphragm valves and knife gate valves are even more inappropriate. The most commonly used on-off valves for steam are gate valves and globe valves. For example, with VTON, the proportion of imported gate valves and imported globe valves used for steam is 86%. So, whether it is better to choose imported gate valves or imported globe valves, this article will focus on the analysis.
The difference between globe valve and gate valve:
1. Sealing surface: The sealing of the stop valve is mandatory and must rely on pressure from external objects to achieve sealing. When the stop valve is fully closed, the valve core and the sealing surface will be in contact with each other, but because there is not much contact between them and the relative slippage is small, the wear on the sealing surface is not great, but the wear on the sealing surface Most of them are damaged due to high-speed erosion of the medium and impurities on the sealing surface itself; the gate valve is self-sealing, relying on the pressure generated by the fluid flow to press the sealing surface against the sealing surface of the valve seat to ensure that the sealing surfaces are tightly overlapped.
2. Flow direction: The flow of VTON stop valve must be from top to bottom; the flow direction of gate valve has no requirement of inlet and outlet direction.
3. Resistance coefficient. The resistance coefficient of ordinary stop valves is about 3.5~4.5. The flow resistance coefficient of ordinary gate valves is about 0.08~0.12.
According to a number of steam projects including Inner Mongolia Shangdu Power Plant, Datang Tuoketuo Power Plant, Beijing Clyde Company, Sichuan Vinylon Power Plant, Chongqing Baihe Power Plant, Chongqing Electric Power Construction Corporation, Fushun Petrochemical Company, Zhejiang Juhua Feedback from the group company, Sinopec Jinan Branch, etc. on the use of Weidun VTON valves has led to the following conclusions:
1. The stop valve has good sealing performance. If it is normally open, you can choose a gate valve. If it is closed for a long time, it is best to use a stop valve, especially VTON's imported bellows stop valve.
2. The gate valve is suitable for full opening and full closing, but it cannot be opened half way, otherwise the gate plate will be damaged, but the pressure drop is small. The stop valve can be opened half way, and it can also have a little adjustment effect, but the pressure drop is large and there is a little rush. Corrosion, the sealing performance is better than the stop valve.
3. Compared with gate valves, the advantages of stop valves are simple structure, good sealing performance, and convenient manufacturing and maintenance; the disadvantages are large liquid resistance and large opening and closing force.
4. The application range of stop valves and gate valves is determined based on their characteristics. In smaller steam channels, when better shut-off sealing is required, inlet stop valves are often used; in larger steam pipelines, since fluid resistance is generally required to be small, inlet gate valves are used.
5. It is especially recommended to use bellows stop valve with double sealing, which has good effect when used on steam pipelines.