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1、 Why is it easy to oscillate when a double seat valve operates with a small opening
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. A double seat valve has two valve cores, the lower valve core being in the flow closed position and the upper valve core being in the flow open position. This way, when working with a small opening, the flow closed valve core is prone to cause vibration of the valve, which is why a double seat valve cannot be used for working with a small opening.
2、 Why dual seal valves cannot be used as shut-off valves
The advantage of the dual seat valve core is its force balanced structure, allowing a large differential pressure, while its prominent disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in large leakage. "If it is used artificially and compulsorily in cutting off situations, the effect is obviously not good, and even if many improvements have been made to it (such as dual seal sleeve valves), it is not advisable.".
3、 What kind of straight stroke control valve has poor anti blocking performance, while angular stroke valve has good anti blocking performance
The valve core of a straight stroke valve is vertically throttled, while the medium flows in and out horizontally. The flow path in the valve chamber inevitably turns upside down, making the flow path of the valve quite complex (such as an inverted "S" shape). In this way, there are many dead zones that provide space for the precipitation of the medium, which in the long run can cause blockage. The throttling direction of the angle travel valve is the horizontal direction. The medium flows in and out horizontally, easily taking away dirty medium. At the same time, the flow path is simple, and there is little space for medium precipitation. Therefore, the angle travel valve has good anti blocking performance.
4、 Why is the stem of a straight stroke regulating valve thinner
It involves a simple mechanical principle: large sliding friction and small rolling friction. When the valve stem of a straight stroke valve moves up and down, and the packing is slightly pressed, it will wrap the valve stem tightly, causing a large return difference. For this reason, the valve rod is designed to be very small, and tetrafluoroethylene packing with a small friction coefficient is often used as packing to reduce the return difference. However, the problem caused by this is that the valve rod is thin, easy to bend, and the packing life is also short. The solution to this problem is to use a rotary valve stem, which is an angle stroke type control valve. Its stem is 2 to 3 times thicker than the straight stroke valve stem, and use graphite packing with a long service life. The valve stem has good stiffness and long packing life, but its friction torque is small and the return difference is small.
5、 Why is the cutoff pressure difference large for angle stroke valves?
The large cutoff pressure difference of angular stroke valves is due to the small torque generated by the resultant force of the medium on the valve core or valve plate on the rotating shaft. Therefore, they can withstand large pressure differences.
6、 Why does the use of rubber lined butterfly valves and fluorine lined diaphragm valves for demineralized water media have a short service life?
Demineralized water media contain low concentrations of acids or bases, which have greater corrosivity to rubber. The corrosion of rubber is manifested by expansion, aging, and low strength. The use effect of rubber lined butterfly valves and diaphragm valves is poor, which is essentially caused by the lack of corrosion resistance of rubber. The rear rubber lined diaphragm valve was improved to a fluorine lined diaphragm valve with good corrosion resistance, but the membrane of the fluorine lined diaphragm valve could not withstand folding up and down and was broken, causing mechanical damage and shortening the valve's life. The current method is to use a special ball valve for water treatment, which can be used for 5 to 8 years.
7、 Why should hard seals be used for shut-off valves
The lower the leakage of the shut-off valve, the better. The leakage of the soft seal valve is low. The shut-off effect is of course good, but it is not wear-resistant and has poor reliability. From the dual standards of small leakage and reliable sealing, soft seal cutting is not as good as hard seal cutting. For example, the fully functional ultra light control valve is sealed and stacked with wear-resistant alloy protection, with high reliability and a leakage rate of 10 to 7, which can already meet the requirements of shut-off valves.
8、 Why did the sleeve valve replace the single and double seat valve but not achieve the desired result
The sleeve valve, which came out in the 1960s, was widely used at home and abroad in the 1970s. In the 1980s, sleeve valves accounted for a large proportion of petrochemical plants introduced. At that time, many people believed that sleeve valves could replace single and double seat valves and become the second generation of products. Today, this is not the case. Single seat valves, double seat valves, and sleeve valves are all used equally. This is because sleeve valves only improve the throttling form, stability, and maintenance compared to single seat valves, but their weight, anti blocking, and leakage indicators are consistent with those of single and double seat valves. How can they replace single and double seat valves? Therefore, they can only be used together.
9、 Why Selection Is More Important Than Calculation
Compared to type selection, calculation is much more important and complex. "Because calculation is only a simple formula calculation, its essence does not lie in the accuracy of the formula, but rather in the accuracy of the given process parameters.". The selection involves a lot of content, and a slight carelessness can lead to improper selection, which not only leads to a waste of human, material, and financial resources, but also leads to unsatisfactory use effects, resulting in several usage issues, such as reliability, service life, and operation quality.
