1. Why does the double-seat valve vibrate briefly during small opening operation For a single core, when the medium is a flow-open type, the valve has good stability; When the medium is a flow-closed type, the stability of the valve is poor. The double-seat valve has two spools, the lower spool is in the flow closed, and the upper spool is in the flow open, so that in the small opening operation, the flow closed type of spool will briefly cause the vibration of the valve, which is the reason why the double seat valve can not be used for small opening operation.
2. Why can't the double seal valve be used as a shut-off valve The advantage of the double seat valve spool is that the force balance structure allows a large pressure difference, and 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 forcibly used in the interpolation occasion, it is obviously not effective, even if many improvements have been made to it (such as double seal sleeve valves), it is not advisable.
3. What is the poor anti-blocking performance of the linear control valve, and the anti-blocking performance of the quarter-stroke valve is good The valve core of the linear valve is vertically throttled, and the medium is horizontally flowing in and out, and the flow channel in the valve cavity will inevitably turn backwards, so that the flow path of the valve becomes appropriately messy (the shape is like an inverted "S" type). In this way, there are many dead zones that provide space for the deposition of the medium, and in the long run, a blockage is formed. The direction of throttling of the quarter-turn valve is the horizontal direction, the medium flows in horizontally and flows out horizontally, and the unclean medium is taken away briefly, and the flow path is simple, and the space for medium deposition is also very small, so the quarter-turn valve has good anti-blocking performance.
Fourth, why the stem of the linear control valve is thinner It touches on a simple mechanical principle: large sliding friction and small rolling friction. The stem of the linear valve moves up and down, and the packing is slightly compressed, which will wrap the stem very tightly, resulting in a large return difference. For this reason, the valve stem is planned very finely, and the packing is often used with a small friction coefficient PTFE packing to reduce the return difference, but the problem is that the valve stem is thin, it is easy to bend, and the packing life is also short. To deal with this problem, the best way is to use the stem of the travel valve strain, that is, the angle stroke type of control valve, its stem is 2-3 times thicker than the straight stroke valve stem, and the use of graphite packing with long life, the stem stiffness is good, the packing life is long, and the friction torque is small, and the return difference is small.
5. Why is the blockage pressure difference of quarter-turn valves large? The blockage pressure difference of the quarter-turn valve is large, because the resultant force generated by the medium on the valve core or valve plate is very small to the torque generated by the rotating shaft, so it can withstand a large pressure difference.
6. Why is the use of rubber-lined butterfly valves and fluorine-lined diaphragm valves for demineralized water medium with short service life? Demineralized water media contain low concentrations of acids or alkalis, which are highly corrosive to rubber. The corrosion of rubber is manifested as swelling, aging, and low strength, and the butterfly valve and diaphragm valve with rubber lining are poorly used, and its essence is formed by the fact that rubber is not corrosion-resistant. The back-lined diaphragm valve is improved to a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve cannot withstand folding up and down and is broken, resulting in mechanical damage, and the life of the valve becomes shorter. Now the best way is to use a special ball valve for water treatment, which can be used for 5-8 years.
7. Why should the plugging valve be as hard as possible The plugging valve requires the leakage to be as low as possible, and the leakage of the soft seal valve is the lowest, and the plugging effect is of course good, but it is not wear-resistant and has poor reliability. From the double standard of small leakage and reliable sealing, soft seal plugging is not as good as hard seal plugging. For example, the full-function ultra-light control valve, sealed and stacked with wear-resistant alloy protection, high reliability, leakage rate of 10-7, can now meet the requirements of the plug-in valve.
8. Why did the sleeve valve replace the single and double seat valves but did not get what they wanted The sleeve valve that came out in the 60s of the 20th century, was widely used at home and abroad in the 70s, and the sleeve valve accounted for a large proportion of the petrochemical equipment introduced in the 80s. Nowadays, this is not the case, and single-seat valves, double-seat valves, and sleeve valves are all used equally. This is due to the fact that the sleeve valve only improves the throttling form, stability and protection is better than the single-seat valve, but its weight, anti-blocking and leakage indicators are consistent with the single-seat and double-seat valves, how can it replace the single-seat and double-seat valves? Therefore, it can only be used together.
9. Why selection is more important than accounting Compared with accounting and selection, selection is much more important and messy. Since accounting is only a brief formula accounting, it itself does not depend on the accuracy of the formula, but on the accuracy of the given process parameters. The selection touches on the content more, a little careless, it will lead to improper selection, not only the formation of manpower, material resources, financial resources, but also the use of the role is not ambitious, bringing a number of use problems, such as reliability, life, operation quality, etc.
10. Why is the piston actuator used more and more in the pneumatic valve For the pneumatic valve, the piston actuator can make full use of the air source pressure, so that the scale of the actuator is finer and thrust is greater than that of the film type, and the O-ring in the piston is also more reliable than the film, so it will be used more and more.
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