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 flow closed, the stability of the valve is poor. A double seat valve has two valve cores, with the lower valve core in the closed position and the upper valve core in the open position. This way, when working at a small opening, the closed valve core is prone to causing valve vibration, which is why a double seat valve cannot be used for working at a small opening.
2、 Why dual seal valves cannot be used as shut-off valves
The advantage of a double seat valve core is its force balance structure, which allows for a large pressure difference. However, its prominent disadvantage is that the two sealing surfaces cannot make good contact at the same time, resulting in large leakage. If it is artificially and forcibly used for cutting off situations, the effect is obviously not good, and even if many improvements have been made to it (such as double sealed sleeve valves), it is still not advisable.
3、 What kind of straight stroke control valve has poor anti blocking performance, while angle 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 channel in the valve chamber inevitably turns and turns, making the flow path of the valve quite complex (shaped like 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 in the horizontal direction, where the medium flows in and out horizontally, easily taking away unclean medium. At the same time, the flow path is simple, and there is little space for medium precipitation, so 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: high sliding friction and low rolling friction. The stem of a straight stroke valve moves up and down, and if the packing is slightly compressed, it will wrap the stem tightly, resulting in a large backlash. For this reason, the valve stem is designed to be very small, and PTFE fillers with small friction coefficients are commonly used as fillers to reduce backlash. However, the problem caused by this is that the valve stem is thin, making it easy to bend, and the packing life is also short. A good way to solve this problem is to use a rotary valve stem, which is an angle stroke type control valve. Its stem is 2-3 times thicker than the straight stroke valve stem, and graphite packing with long service life is used. The valve stem has good stiffness and long packing life, but its friction torque is actually small and the return difference is small.
5、 Why is the cutoff pressure difference large for angle stroke valves?
The cutting pressure difference of angle stroke valves is relatively large because the combined force generated by the medium on the valve core or valve plate has a very small torque on the rotating shaft, so it can withstand a large pressure difference.
6、 Why do desalinated water media use rubber lined butterfly valves and fluorine lined diaphragm valves with short service life?
The desalinated water medium contains low concentrations of acids or bases, which have significant corrosiveness to rubber. The corrosion of rubber manifests as expansion, aging, and low strength. The poor performance of butterfly and diaphragm valves with rubber lining is essentially due to the lack of corrosion resistance of rubber. The rear rubber lined diaphragm valve has been 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, causing mechanical damage and shortening the valve's lifespan. The best solution now is to use specialized ball valves for water treatment, which can be used for 5-8 years.
7、 Why should hard seals be used as much as possible for shut-off valves
The cut-off valve requires a lower leakage as much as possible. The leakage of a soft sealing valve is lower, and the cut-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 regulating valve is sealed and protected by wear-resistant alloy, with high reliability and a leakage rate of 10-7, which can already meet the requirements of the shut-off valve.
8、 Why did sleeve valves replace single and double seat valves but not achieve their desired results
The sleeve valve, which was introduced in the 1960s, was widely used both domestically and internationally in the 1970s. In the petrochemical plants introduced in the 1980s, the proportion of sleeve valves was relatively large. At that time, many people believed that sleeve valves could replace single and double seat valves and become the second-generation products. Until now, this is not the case. Single seat valves, double seat valves, and sleeve valves are all used equally. (Recommended by valve manufacturer: Shandong Guowei Valve Manufacturing Co., Ltd.) This is because the sleeve valve only improves the throttling form, stability, and maintenance compared to single seat valves, but its weight, anti blockage, and leakage indicators are consistent with single and double seat valves. How can it replace single and double seat valves? So, it can only be used together.
9、 Why is selection more important than calculation
Compared to selection, calculation and selection are much more important and complex. Because calculation is just a simple formula calculation, its essence lies not in the accuracy of the formula, but 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 waste of manpower, material resources, and financial resources, but also results in unsatisfactory usage effects, leading to several usage issues such as reliability, lifespan, and operational quality.
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