1. The double-seat valve is prone to oscillation when working with a small opening. For a single core, when the medium is open flow, the valve has good stability; when the medium is flow closed, the valve has poor stability. . The double-seat valve has two valve cores. The lower valve core is in flow-closed state and the upper valve core is in flow-open state. In this way, when working at a small opening, the closed-flow valve core can easily cause vibration of the valve. This is a double-seat valve. The reason why it cannot be used for small opening work. 2. The double-seal valve cannot be used as a cut-off valve. The advantage of the double-seat valve core is that it has a force-balanced structure that allows a large pressure difference. However, its outstanding disadvantage is that the two sealing surfaces cannot be in good contact at the same time, causing large leakage. If it is used artificially and compulsorily in cutting-off situations, the effect will obviously not be good. Even if many improvements are made for it (such as double sealing sleeve valve), it is not advisable. 3. The valve stem of the straight stroke regulating valve is thinner. It involves a simple mechanical principle: large sliding friction and small rolling friction. The valve stem of a straight stroke valve moves up and down. If the packing is pressed a little tighter, it will wrap the valve stem very tightly, resulting in a large hysteresis. To this end, the valve stem is designed to be very small, and the packing often uses PTFE packing with a small friction coefficient in order to reduce the hysteresis. However, the problem derived from this is that a thin valve stem is easy to bend, and the packing life is also short. To solve this problem, the best way is to use a rotary valve stem, that is, a rotary stroke regulating valve. Its valve stem is 2 to 3 times thicker than a straight stroke valve stem, and it uses graphite filler with long life and high valve stem stiffness. Good, the filler has a long life, its friction torque is small, and the hysteresis is small. 4. What kind of straight stroke control valve has poor anti-blocking performance, while the angle stroke valve has good anti-blocking performance? The straight stroke valve core is vertical throttling, and the medium flows in and out horizontally. The flow path in the valve cavity must turn and reverse, causing the valve to The flow path becomes quite complex (shaped like an inverted "S"). In this way, there are many dead zones, which provide space for the sedimentation of the medium, which in the long run will cause blockage. The throttling direction of the quarter-turn valve is the horizontal direction. The medium flows in horizontally and flows out horizontally, which can easily take away the dirty medium. At the same time, the flow path is simple and there is little space for the medium to settle, so the quarter-turn valve has good anti-blocking performance. 5. The cut-off pressure difference of the quarter-turn valve is large. The cut-off pressure difference of the quarter-turn valve is large because the resultant force generated by the medium on the valve core or valve plate exerts a very small torque on the rotating shaft. Therefore, it can withstand a relatively large amount of pressure. Large pressure difference. 6. The desalted water medium uses rubber-lined butterfly valves and fluorine-lined diaphragm valves with short service life. The desalted water medium contains low concentrations of acids or alkalis, which are highly corrosive to rubber. Corrosion of rubber manifests as expansion, aging, and low strength. Butterfly valves and diaphragm valves lined with rubber have poor performance. The essence is that rubber is not resistant to corrosion. The rubber-lined diaphragm valve was improved to a fluorine-lined diaphragm valve with good corrosion resistance. However, the diaphragm of the fluorine-lined diaphragm valve could not withstand folding up and down and was broken, causing mechanical damage and shortening the life of the valve. The best way now is to use a special ball valve for water treatment, which can be used for 5 to 8 years. 7. The cut-off valve should try to use a hard seal. The cut-off valve requires the lower the leakage, the better. The leakage of the soft seal valve is the lowest. Of course, the cut-off effect is good, but it is not wear-resistant and has poor reliability. From the dual standards of small leakage and reliable sealing, soft seal cutting is not as good as hard seal cutting. For example, the full-function ultra-light control valve is sealed and protected by wear-resistant alloy. It has high reliability and a leakage rate of 10 to 7, which can already meet the requirements of a shut-off valve. 8. Model selection is more important than calculation. Comparing calculation with model selection, model selection is much more important and complicated. Because the calculation is just a simple formula calculation, it does not depend on the accuracy of the formula itself, but on whether the given process parameters are accurate. Selection involves a lot of content, and if you are not careful, it will lead to improper selection, which will not only cause a waste of manpower, material resources, and financial resources, but also the use effect is not ideal, causing several use problems, such as reliability, lifespan, and operation. Quality etc. 9. Piston actuators will be used more and more in pneumatic valves. For pneumatic valves, the piston actuator can make full use of the air source pressure, making the actuator smaller and more powerful than the diaphragm type. The O in the piston Rings are also more reliable than membranes, so their use will increase.
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