You should know, valve also has its temper!

The lower the leakage of the shut-off valve, 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.

1. Why is it easy to oscillate when the double seat valve works with small opening?
For single core, the valve has good stability when the medium is flow open type, and poor stability when the medium is flow closed type. 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, when the valve operates at a small opening, the flow closed valve core is easy to cause valve vibration, which is the reason why the double seat valve can not be used for small opening work.

2. Why can’t double seal valve be used as shut-off valve?
The advantage of double seat valve core is the force balance structure, allowing large pressure difference, but its outstanding disadvantage is that the two sealing surfaces can not be in good contact at the same time, resulting in large leakage. If it is artificially and compulsorily used in the cut-off situation, the effect is obviously not good. Even if many improvements have been made for it (such as double sealed sleeve valve), it is not advisable.

3. What kind of straight stroke control valve has poor anti blocking performance and angular travel valve has good anti blocking performance?
The valve core of straight stroke valve is vertical throttling, and the medium is horizontal flow in and out, so the flow path in the valve chamber must turn and reverse, which makes the flow path of the valve become quite complex (the shape is like inverted “s” shape). In this way, there are many dead zones, which provide space for the precipitation of the medium and cause blockage in the long run. The throttling direction of the angular travel valve is horizontal direction. The medium flows in and out horizontally, so it is easy to take away the unclean medium. At the same time, the flow path is simple and the space for medium precipitation is very small, so the anti blocking performance of the angular travel valve is good.  
4. Why is the stem of straight stroke control valve thinner?

It involves a simple mechanical principle: large sliding friction and small rolling friction. The stem of the straight stroke valve moves up and down. If the packing is pressed a little bit, it will wrap the valve rod tightly and produce a large return difference. For this reason, the valve stem is designed to be very small, and the packing is often used with PTFE packing with small friction coefficient, so as to reduce the return error. However, the problem is that the valve stem is thin, which is easy to bend and the packing life is short. The best way to solve this problem is to use the rotary valve stem, that is, the angle stroke type control valve. Its stem is 2-3 times thicker than the straight stroke valve stem, and the graphite packing with long service life is selected. The valve rod stiffness is good, the packing life is long, and its friction torque is small and the return difference is small.  

5. Why is the cut-off pressure difference of angle stroke valve larger?
The larger cut-off pressure difference of angle stroke valve is because the resultant force generated by the medium on the valve core or valve plate produces very small torque on the rotating shaft, so it can withstand large pressure difference.

6. Why is the service life of rubber lined butterfly valve and fluorine lined diaphragm valve used in desalted water medium short?
There are low concentration acid or alkali in the desalted water medium, which are corrosive to rubber. Rubber corrosion performance for expansion, aging, low strength, with rubber lined butterfly valve, diaphragm valve use effect is poor, its essence is rubber corrosion resistance. The back rubber lined diaphragm valve was improved to a fluorine lined diaphragm valve with good corrosion resistance. However, the membrane of the fluorine lined diaphragm valve could not withstand folding up and down, causing mechanical damage and shortening the service life of the valve. Now the best way is to use special ball valve for water treatment, which can be used for 5-8 years.  

7. Why should the shut-off valve be hard sealed?
The lower the leakage of the shut-off valve, 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. According to the double standards of small leakage and reliable sealing, soft sealing is better than hard sealing. Such as full-function ultra light control valve, sealed and stacked with wear-resistant alloy protection, high reliability, leakage rate of 10-7, has been able to meet the requirements of the shut-off valve.

8. Why did not sleeve valve replace single and double seat valve?
Sleeve valves, which came out in the 1960s, were widely used at home and abroad in the 1970s. In the petrochemical plants introduced in the 1980s, sleeve valves accounted for a large proportion. At that time, many people believed that sleeve valves could replace single and double seat valves and become the second generation products. Up to now, it is not so. 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, but its weight, anti blocking and leakage indicators are consistent with those of single seat valve and double seat valve. How can it replace single seat valve and double seat valve? Therefore, they can only be used together.  

9. Why is selection more important than calculation?
Compared with the calculation, the type selection is much more important and complicated. Because the calculation is only a simple formula calculation, it does not depend on the accuracy of the formula itself, but on the accuracy of the given process parameters. There are many contents involved in the model selection. If it is not careful, it will lead to improper selection, which will not only cause waste of manpower, material resources and financial resources, but also cause some problems in use, such as reliability, service life and operation quality.