1. Why should the shut-off valve be hard-sealed as much as possible?
The lower the leak, the better the leakage is required. The leakage of the soft-sealed valve is the lowest, and the cutting effect is of course good, but it is not wear-resistant and has poor reliability. From the double standard of small leakage, sealing and reliability, the soft seal cut is not as good as the hard seal cut. Such as full-featured ultra-light regulating valve, sealed and covered with wear-resistant alloy protection, high reliability, leakage rate of 10-7, has been able to meet the requirements of the shut-off valve.
2. Why can't the double seal valve be used as a shut-off valve?
The advantage of the two-seat valve spool is the force-balanced structure, which allows a large differential pressure, and its outstanding disadvantage is that the two sealing faces cannot be in good contact at the same time, resulting in a large leak. If it is artificially and forcibly used to cut off the occasion, it is obviously not effective, even if it has made many improvements (such as double-sealed sleeve valves), it is not advisable.
3. Why does the double seat valve easily oscillate when working at a small opening?
For a single core, the valve stability is good when the medium is flow-opening; the stability of the valve is poor when the medium is flow-closed. The double seat valve has two spools, the lower spool is closed, and the upper spool is open. Thus, when working at a small opening, the flow-closed spool is liable to cause vibration of the valve. This is a double seat valve. Can not be used for small opening work.
4. What is the anti-blocking performance of the straight stroke regulating valve, and the anti-blocking performance of the angular stroke valve is good?
The spool of the straight stroke valve is vertically throttled, and the medium flows horizontally in and out. The flow passage in the valve chamber must turn and turn backwards, making the flow path of the valve quite complicated (the shape is inverted "S" type). In this way, there are many dead zones that provide space for the precipitation of the medium, which in the long run causes blockage. The direction of the angular stroke valve throttling is the horizontal direction. The medium flows horizontally and horizontally, which makes it easy to take away the dirty medium. At the same time, the flow path is simple, and the space for the medium to precipitate is also small, so the anti-blocking performance of the angular stroke valve is good.
5. Why is the valve stem of the straight stroke control valve thinner?
The straight stroke adjustment valve involves a simple mechanical principle: large sliding friction and low rolling friction. The valve stem of the straight stroke valve moves up and down, and the packing is slightly pressed tightly, which will tightly seal the valve stem and produce a large backlash. For this reason, the valve stem is designed to be very small, and the filler is also commonly used with a small friction coefficient of PTFE filler to reduce the backlash, but the problem is that the valve stem is thin, the bend is easy, and the filler life is short. The best way to solve this problem is to use the travel valve stem, that is, the angular stroke type regulating valve. Its valve stem is 2 to 3 times thicker than the straight stroke valve stem, and the graphite packing with long life is selected. Well, the filler has a long service life, and the friction torque is small and the backlash is small.
6. Why is the cut-off pressure difference of the angular stroke type valve larger?
The cut-off pressure difference of the angular stroke type valve is large because the resultant force of the medium on the valve core or the valve plate generates a very small torque to the rotating shaft, and therefore, it can withstand a large pressure difference.
7. Why does the sleeve valve replace the single and double seat valve but does not have the wish?
The sleeve valve that was introduced in the 1960s was widely used at home and abroad in the 1970s. The proportion of the sleeve valve in the petrochemical plant introduced in the 1980s was large. At that time, many people believed that the sleeve valve could replace the single and double seat valves. Become a second generation product. This is not the case today, single-seat valves, double-seat valves, and sleeve valves 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, anti-blocking and leakage indicators are consistent with single and double seat valves. How can it replace single and double seat valves? What? Therefore, they can only be used together.
8. Why does the demineralized water medium use a rubber-lined butterfly valve and a fluorine-lined diaphragm valve with a short service life?
Demineralized media contain low concentrations of acids or bases which are highly 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 effect, and the essence is that the rubber is not resistant to corrosion. The back-lined rubber diaphragm valve is improved to a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve can be broken by being folded up and down, causing mechanical damage and shortening the life of the valve.
The best way to do this now is to use a special ball valve for water treatment, which can be used for 5 to 8 years.
9. Why are piston actuators used more and more in pneumatic valves?
For pneumatic valves, the piston actuator can make full use of the air supply pressure, making the actuator smaller in size than the diaphragm type, and the thrust is larger. The O-ring in the piston is also more reliable than the film, so its use will become more and more many.
10. Why is selection more important than calculation?
Compared with the selection, the selection is much more important and more complicated. Because the calculation is just a simple formula calculation, it is not in itself the accuracy of the formula, but rather whether the given process parameters are accurate. There are many contents involved in the selection. If you are not careful, it will lead to improper selection, which not only causes waste of manpower, material resources and financial resources, but also has unsatisfactory effect, which brings about some use problems such as reliability, longevity and operation. Quality and so on.
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Label: Ten problems often encountered in the daily use of valves
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