The selection of common valves should be analyzed from six aspects, to consider, to pay attention.
1. First of all, we first analyze the requirements of the valve: ordinary ball valve, butterfly valve , and stop valve are strictly prohibited for adjustment according to their structural characteristics. However, in process design, it is commonly used for conditioning. Due to the adjustment and use, the valve seal is in a throttling state for a long time, the impurities in the oil scouring the seal, damaging the sealing surface, causing the closure to be unsatisfactory or because the operator has sealed the sealing surface to cause damage, causing the valve to pass, and opening the imagination
The installation position of the valve is unreasonable. When the medium contains impurities, no filter is installed at the front end to allow impurities to enter the valve interior, causing damage to the sealing surface, or impurities are deposited on the bottom of the valve, causing the valve to be closed tightly and causing leakage.
2, from the perspective of industrial requirements, first of all, for corrosive media, if the temperature and pressure are not high, non-metallic valves, such as plastic ball valves , plastic butterfly valves, plastic diaphragm valves, etc., should be used, if the temperature is high and the pressure is high. Fluorine-lined valves are available to save precious metals. In the selection of non-metallic valves, economic rationality should be considered. When the medium is special medium such as oxygen or ammonia, a special oxygen valve or ammonia valve should be used.
For some media with crystals or sediments, it is not advisable to use shut-off valves and gate valves because their sealing faces are prone to wear by the deposits and cause leakage of the media. Therefore, the ball valve is more suitable, and the slab gate valve can also be used, but the Zui is better to use the jacket valve.
Generally, the valves on the water and steam pipes can be cast iron valves. However, if the outdoor steam pipes are shut off, they will cause icing and thus freeze the valves. Therefore, in cold regions, the valves are made of cast steel, low-temperature steel or effectively insulated. The measures are good.
Gate valves, globe valves and ball valves are large valves with a large amount of valve usage. The gate valve has strong circulation capacity and low energy consumption of the conveying medium, but according to the large space, the stop valve has simple structure and convenient maintenance, but the flow resistance is large. The ball valve has low flow resistance and fast opening and closing characteristics, but the use temperature is limited. In the medium with high viscosity such as petroleum products, the gate valve is mostly used in consideration of the strong flow capacity of the gate valve, and the shut-off valve should be used on the water and steam pipelines. The pressure drop is not large, so the shut-off valve is in the water, steam and other medium pipelines. In the middle, the ball valve can be used under the conditions of use.
3. From the perspective of convenient operation , for large diameter valves and long distance, high altitude high temperature and high pressure, electric and pneumatic valves should be used. For flammable occasions, explosion-proof devices should be used. For safety and reliability, hydraulic and pneumatic devices should be applied. . For valves that need to be opened quickly and closed quickly, butterfly valves, ball valves, plug valves and other valves should be used as needed. It is not suitable for the selection of gate valve and stop valve.
4, from the temperature and pressure resistance capacity should be more high temperature and high pressure medium often used castings of bismuth molybdenum steel, for ultra-high temperature and high pressure medium should consider the use of its corresponding forgings, the overall performance of forgings is higher than castings.
5. When it is necessary to accurately adjust the accuracy of the flow adjustment, the regulating valve should be used. When the accuracy of the small flow rate needs to be adjusted, the needle valve should be used. When it is necessary to reduce the post-valve pressure, a pressure reducing valve should be used. When it is necessary to maintain the stability of the valve pressure, a pressure reducing valve should be used.
6, from the cleanability ability to consider food and bioengineering production and transportation process pipeline requirements on the valve need to consider the cleanliness of the medium, the general gate valve and stop valve can not be guaranteed. From the standpoint of cleanliness, no valve can be compared to a diaphragm valve.
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