1. Why should the block valve be hard sealed?

The lower the leakage of the blocking valve, the better. The leakage of the soft seal valve is low. Of course, the blocking effect is good, but it is not wear-resistant and has poor reliability. Judging from the double standards of small leakage and reliable sealing, soft sealing plugging is not as good as hard sealing plugging. For example, the full-featured ultra light regulating valve is sealed and stacked with wear-resistant alloy for maintenance, which is highly reliable and has a leakage rate of 10-7, and can now meet the requirements of the blocking valve.

2. Why can't a double seal valve be used as a block valve?

The strength of the double seat valve core is the force balance structure, which allows a large pressure difference. Its prominent defect is that the two sealing surfaces cannot contact well at the same time, resulting in large leakage. If it is artificially and compulsorily used for blocking, it obviously does not work well. Even if it has made many improvements (such as double seal sleeve valve), it is not advisable.

3. Why does the double seat valve vibrate slightly when operating at a small opening? IMO agent

For single core, when the medium is flow open, the valve has good stability; When the medium is flow closed, the stability of the valve is poor. The double seat valve has two valve cores, the lower valve core is in the flow closed position, and the upper valve core is in the flow open position. In this way, the flow closed valve core will briefly cause the vibration of the valve during the small opening operation, which is the reason why the double seat valve cannot be used for the small opening operation.

4. What kind of straight stroke control valve has poor anti blocking function and angle stroke valve has good anti blocking function?

The straight stroke valve core is straight throttling, while the medium flows in and out horizontally. The flow passage in the valve chamber must turn and reverse, making the flow path of the valve properly disordered (shaped like an inverted "S"). In this way, there are many dead zones, which provide space for the deposition of media, and as time passes, blocking occurs. The throttling direction of the angle travel valve is the horizontal direction. The medium flows in and out horizontally, taking away the unclean medium. At the same time, the flow path is simple, and the space for medium deposition is small, so the angle travel valve has a good anti blocking function.

5. Why is the stem of straight stroke control valve thinner?

It touches upon a simple mechanical principle: large sliding friction and small rolling friction. When the stem of the straight travel valve moves up and down, if the packing is slightly compressed, it will wrap the stem tightly, causing a large return difference. For this reason, the valve stem is designed very carefully, and the packing is usually made of tetrafluoro packing with small friction coefficient in order to reduce the backlash. However, the problem is that the valve stem is thin, so it is easy to bend, and the life of the packing is short. The way to solve this problem is to use the travel valve stem, that is, the angle travel control valve stem. Its stem is 2 to 3 times thicker than the straight travel valve stem, and graphite packing with long life is used. With good stem stiffness and long life of packing, its friction torque is small and the return difference is small.

6. Why is the blocking pressure difference of angle travel valve large?

The blocking pressure difference of angle travel valve is large, because the resultant force of the medium on the valve core or valve plate has very small torque on the rotating shaft, so it can accept a large pressure difference.

7. Why did the sleeve valve replace the single seat valve and the double seat valve, but it did not succeed? ALLWEILER

The sleeve valve, which came out in the 1960s, was widely used at home and abroad in the 1970s. The sleeve valve accounted for a large proportion of petrochemical equipment introduced in the 1980s. At that time, many people believed that the sleeve valve could replace single and double seat valves and become the second generation product. Up to now, this is not the case. Single seat valve, double seat valve and 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 component, anti blocking and leakage indicators are the same as the single seat valve and the double seat valve. How can it replace the single seat valve and the double seat valve? Therefore, they can only be used together.

8. Why is the service life of rubber lined butterfly valve and fluorine lined diaphragm valve for desalted water medium short?

The desalted water medium contains low concentration acids or alkalis, which are corrosive to rubber. The corrosion of rubber is characterized by expansion, aging and low strength. The butterfly valve and diaphragm valve with rubber lining have poor application effect, which is actually caused by the non corrosion resistance of rubber. The back rubber lined diaphragm valve is improved to be a fluorine lined diaphragm valve with good corrosion resistance function, but the diaphragm of the fluorine lined diaphragm valve can not withstand folding up and down and is broken, resulting in mechanical damage and shortening the life of the valve.

The current method is special ball valve for water treatment, which can be used for 5-8 years.

9. Why are more and more piston actuators used in pneumatic valves?

For pneumatic valves, the piston actuator can make full use of the air source pressure to make the actuator smaller and more compact than the membrane actuator, with greater thrust, and the O-ring in the piston is also more secure than the membrane actuator, so it will be used more and more.

10. Why is selection more important than accounting?

Compared with model selection, model selection is much more important and messy. Since accounting is only a simple formula accounting, it does not depend on the accuracy of the formula itself, but on the accuracy of the given process parameters. Model selection involves a lot of content, and a little carelessness will lead to improper model selection, which will not only result in the waste of human, material and financial resources, but also lead to some application problems, such as reliability, longevity, operation quality, etc.