Valve use common problems

1. Why is the double seat valve easy to oscillate when working with a small opening? For a single core, when the medium is a flow-open type, the valve stability is good; when the medium is a flow-closed type, the valve stability is poor. The double-seat valve has two spools, the lower spool is in flow-closed, and the upper spool is in flow-open. In this way, when working with a small opening, the flow-closed spool is easy to cause valve vibration. This is the double-seat valve. The reason why it cannot be used for small opening work. 2. Why can't the double seal valve be used as a shut-off valve? The advantage of the double seat valve spool is the force balance structure, which allows a large pressure difference, but its outstanding disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in large leakage. If it is artificially and forcibly used for cutting off occasions, the effect is obviously not good. Even if many improvements are made for it (such as double-sealed sleeve valve), it is not advisable. 3. Which straight-stroke regulating valve has poor anti-blocking performance and angular-stroke valve has good anti-blocking performance? The spool of the straight-stroke valve is a vertical throttling, and the medium flows in and out horizontally, and the flow path in the valve cavity must turn and reverse, which makes the flow path of the valve quite complicated (shaped like an inverted 'S' shape). In this way, 4. Why is the stem of the straight-stroke regulating valve thinner? It involves a simple mechanical principle: high sliding friction and low rolling friction. The valve stem of the straight-stroke valve moves up and down, and the packing is slightly compressed, it will wrap the valve stem tightly, resulting in a large return difference. For this reason, the valve stem is designed to be very small, and the packing is usually made of tetrafluoro packing with a small friction coefficient to reduce the return difference, but the problem is that the valve stem is thin, easy to bend, and the packing life is short. The best way to solve this problem is to use a travel valve stem, that is, an angular travel control valve. Its stem is 2 to 3 times thicker than a straight travel stem, and a long-life graphite packing is used, and the stem stiffness Well, the packing life is long, the friction torque is small, and the return difference is small. 5. Why is the cut-off pressure difference of the angular stroke valve large? The cut-off pressure difference of the angular stroke valve is large because the resultant force generated by the medium on the valve core or the valve plate has a very small torque on the rotating shaft, so it can withstand a large pressure difference. 6. Why use rubber-lined butterfly valve and fluorine-lined diaphragm valve for desalinated water medium with short service life? The desalted water medium contains a low concentration of acid or alkali, which are more corrosive to rubber. The corrosion of rubber is manifested as expansion, aging, and low strength. Butterfly valves and diaphragm valves with rubber lining have poor use effects. The essence is that rubber is not resistant to corrosion. The rubber-lined diaphragm valve has been improved to a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve cannot withstand being folded up and down and is 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. Why should the shut-off valve use hard seals as much as possible? The cut-off valve requires the lower the leakage, the better. The leakage of the soft-sealed valve is the lowest. Of course, the cut-off effect is good, but it is not wear-resistant and has poor reliability. From the double standard of small leakage and reliable sealing, soft sealing is not as good as hard sealing. For example, the full-function ultra-light regulating valve is sealed and piled with wear-resistant alloy protection, with high reliability and a leakage rate of 10-7, which can already meet the requirements of the shut-off valve. 8. Why did the sleeve valve replace the single and double seat valve but not get what you wanted? The sleeve valve, which came out in the 1960s, was widely used at home and abroad in the 1970s. In the petrochemical plants introduced in the 1980s, the sleeve valve accounted for a large proportion. At that time, many people believed that the sleeve valve could replace the single and double seat valves. , become the second generation product. Up to now, this is not the case, single seat valve, double seat valve, sleeve valve are all used equally. This is because the sleeve valve only improves the throttling form, stability and maintenance better than the single seat valve, but its weight, anti-blocking and leakage indicators are consistent with the single and double seat valves, how can it replace the single and double seat valves Woolen cloth? Therefore, it can only be used together. 9. Why is selection more important than calculation? Compared with calculation and selection, 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, but on whether the given process parameters are accurate. The selection involves a lot of content. A little carelessness will lead to improper selection, which will not only cause manpower, material resources, and financial resources. 10. Why are piston actuators used more and more in pneumatic valves? For pneumatic valves, the piston actuator can make full use of the air source pressure, so that the size of the actuator is smaller and the thrust is larger than that of the diaphragm type, and the O-ring in the piston is also more reliable than the diaphragm, so its use will be more and more many.
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