1. Why can’t the double seal valve be used as a cut-off valve?
The advantage of the two-seat valve core is the force balance structure, allowing large pressure difference, and its prominent disadvantage is that the two sealing surface can not at the same time good contact, resulting in large leakage. If it is used artificially and compulsively in cutting situations, it is clearly not effective, and even many improvements to it (such as double seal sleeve valves) are not desirable.
2. Why is selection more important than calculation?
Compared with the calculation and selection, the selection is much more important and complicated. Because the calculation is only a simple formula calculation, its itself does not depend on the accuracy of the formula, but depends on the accuracy of the given process parameters. The selection involves a lot of content, a little careless, will lead to improper selection, not only cause the waste of manpower, material resources, financial resources, and use effect is not ideal, bring a number of use problems, such as reliability, life, operation quality.
3. Why is the service life of rubber lined butterfly valve and fluorine lined diaphragm valve short for desalinated water medium?
Desalted water medium containing low concentration of acid or alkali, they have larger corrosion in rubber. Rubber corrosion performance for expansion, aging, low intensity, in line with rubber butterfly valve, diaphragm valve use effect is poor, its essence is the rubber is not caused by corrosion. The rear rubber lined diaphragm valve is improved to be a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve can not withstand the upper and lower folding and is broken, causing mechanical damage, the life of the valve is shortened. Now the best way is to use water treatment special ball valve, it can be used for 5 ~ 8 years.
4, why the straight stroke regulating valve stem is thinner?
It involves a simple mechanical principle: large sliding friction, small rolling friction. Straight stroke valve stem up and down movement, packing a little bit compressed, it will put the stem very tight, a large back. To this end, the stem is designed to be very small, packing and commonly used friction coefficient of tetrafluorin packing, in order to reduce backslip, but the problem is sent out of the stem is small, it is easy to bend, packing life is short. To solve this problem, the best way is to use the travel valve stem, that is, the angular stroke type of control valve, its stem than the straight stroke stem thick 2 ~ 3 times, and choose a long life of graphite packing, stem stiffness, packing life is long, but the friction torque is small, the difference is small.
5. Why did the sleeve valve replace the single and two-seat valve but not as desired?
In the 60 s of the sleeve valve, extensive use at home and abroad in the 70 s, 80 s introduced in petrochemical plant of sleeve valve ratio is larger, at that time, many people think, sleeve valve can replace single, two-seat valves, become the second generation product. To now, not so, single – seat valve, double – seat valve, sleeve valve are equally used. This is because the sleeve valve only improves the throttling form, stability and maintenance better than the single seat valve, but its weight, plugging and leakage indicators are the same as the single and double seat valve, how can it replace the single and double seat valve? Therefore, it can only be used together.