If there is a certain gap between the design level and production level of China’s control valve and advanced foreign countries, it is practical, but if there is a very large gap, it may not be in line with reality. So, why is the use effect and time of domestic control valves far behind the imported products?
Just compare the calculation and selection tables of China’s control valves with those in foreign countries, and it is not difficult to find that our content is too simple. For example, there are 49 serial numbers listed in the standard format of the American Institute of Instrumentation, and there are less than 20 serial numbers in the Chinese form. Many of the contents are not included. The selection is inevitably improper and incomplete, resulting in “congenital deficiency”; and the level of domestic control valve standardization is too high. , To respond differently to every change, not to “prescribe the right medicine”. Only taking the leakage of the valve as an example, the user’s feedback is strong. It does not only involve the selection of the structure. It also involves unbalanced force calculations. Who will carefully consider it? No. If it does not, it will inevitably cause usage problems such as undead, unopened, large leakage, and poor reliability of the seal (it can be used at the beginning, but it will not work for a long time). To solve it, it must be carefully considered.
It includes:
- Calculate the unbalanced force according to the closing pressure difference of the valve to determine the valve structure and the size of the actuator. First, ensure the sufficient output force required for closing.
- Determine the best flow direction to facilitate sealing.
- Valve structure considerations. For large pressure difference and large diameter valves (such as DN100 valve, △P=20MPa, its unbalanced thrust is as high as Ft=0.25π×102×20=15.7t), it is very important to carefully consider the structure , Including the consideration of force balance and resistance to cavitation and erosion.
- Considering the anti-blocking performance of dirty media and fouling media, how can it be sealed if it is blocked or stuck?
- For strong corrosive media, the anti-corrosion performance of the throttle is considered, and it must be reliable. Many valves leak beyond the standard soon after operation. The reason is that the throttle is corroded.
- Consideration of sealing type:
a. Hard seal or soft seal;
b. Whether it is necessary to surfacing wear-resistant alloy to improve reliability;
c. Soft seal type and soft seal material. - Leakage level, test method, test pressure difference, acceptance method, etc.
It can be seen that rough consideration will inevitably result in a rough use effect: most general products can be used, so if you consider improperly and special occasions, the valve will definitely not work well.
Therefore, the main problems in the application of China’s regulating valve are: incomplete calculation and selection, resulting in “congenital deficiency”; the manufacturer’s products are too single to meet various needs.
The solution is:
First of all, to grasp the first level of quality (also the one that the manufacturer does not pay attention to) sign a contract, review that the selected valve can really effectively meet the working conditions and use requirements, and overcome “inherent shortcomings”;
Followed by the various products produced by the manufacturer, especially special products and modified products to meet the needs of special occasions. To achieve these two points, both the selection personnel and the manufacturer must be proficient in the application of the regulating valve.