1、 Why is it easy for double seat valves to oscillate when working with a small opening
For a single core, when the medium is a flow open type, the valve stability is good; When the medium is a flow closed type, the stability of the valve is poor. A double seat valve has two valve cores, with the lower core in the flow closed position and the upper core in the flow open position. Therefore, when working at a small opening, the flow closed type valve core is prone to vibration, which is why double seat valves cannot be used for small opening operation.
2、 Why can't double sealed valves be used as shut-off valves
The advantage of the 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 in cutting situations, the effect is obviously not good, even if many improvements have been made to it (such as double sealed sleeve valves), it is not advisable.
3、 What kind of straight stroke regulating 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 inside the valve chamber inevitably turns and twists, making the valve's flow path quite complex (shaped like an inverted "S"). In this way, there are many dead zones that provide space for the precipitation of the medium, which, over time, can cause blockages. The direction of throttling of the angle stroke valve is the horizontal direction, where the medium flows in and out horizontally, making it easy to carry away unclean medium. At the same time, the flow path is simple and there is little space for the medium to settle, so the angle stroke valve has good anti blocking performance.
4、 Why is the straight stroke regulating valve stem 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 tightly wrap the stem, resulting in a large backlash. For this reason, the valve stem is designed to be very small, and PTFE packing with low friction coefficient is commonly used as the packing to reduce backlash. However, the problem with this is that if the valve stem is thin, it is easy to bend and the packing life is short. The best way to solve this problem is to use a travel valve stem, which is a regulating valve with angular stroke. Its stem is 2-3 times thicker than a straight stroke stem, and it uses graphite packing with long service life. The stem stiffness is good, the packing life is long, and its friction torque is small and the backlash is small.
5、 Why is the cut-off pressure difference of angular stroke valves relatively large?
The cutting pressure difference of angular 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 rubber lined butterfly valves and fluorine lined diaphragm valves have a short service life for desalinated water media?
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 valves and diaphragm valves lined with rubber is essentially due to the lack of corrosion resistance of rubber. The back lined rubber 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 up and down folding and is broken, causing mechanical damage and shortening the valve's lifespan. The best solution now is a specialized ball valve for water treatment, which can be used for 5-8 years.
7、 Why should hard seals be selected as much as possible for shut-off valves
The lower the leakage required for a cut-off valve, the better. Soft sealed valves have the lowest leakage and good cut-off effect, but they are not wear-resistant and have poor reliability. From the dual standards of small leakage and reliable sealing, soft seal cutting is not as good as hard seal cutting. As a fully functional ultra lightweight regulating valve, it 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 a shut-off valve.
8、 Why haven't sleeve valves replaced single and double seat valves as desired
The sleeve valve, which was introduced in the 1960s, was widely used both domestically and internationally in the 1970s. In the 1980s, sleeve valves accounted for a large proportion of imported petrochemical plants. 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 have all been used equally. This is because the sleeve valve only improves the throttling form, stability, and maintenance compared to single seat valves, 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? So, it can only be used together.
9、 Why is selection more important than calculation
Compared to calculation and selection, selection is much more important and complex. Because calculation is just a simple formula calculation, its essence lies not in the accuracy of the formula itself, but in whether the given process parameters are accurate. The selection involves a lot of content, and a slight carelessness can lead to improper selection, which not only causes waste of manpower, material resources, and financial resources, but also results in unsatisfactory usage effects, leading to several issues such as reliability, lifespan, and operational quality.
10、 Why are piston actuators increasingly used in pneumatic valves
For pneumatic valves, the piston actuator can fully utilize the air source pressure, making the actuator smaller in size and more powerful than the diaphragm type. The O-ring in the piston is also more reliable than the diaphragm type, so its use will continue to increase.