Electric control valves have a much wider range of applications than pneumatic and hydraulic control valves due to their convenience and durability, without the need for additional air source pipelines or oil pipes. Moreover, when equipped with explosion-proof electric actuators, they can be used in explosion-proof situations. Therefore, electric control valves can basically replace pneumatic control valves and be used in all industrial automation control applications. However, electric control valves and pneumatic control valves each have their own advantages and disadvantages, and must be selected correctly and used reasonably in order to achieve the goal of automation control. The following are some common problems and solutions during the use of electric and pneumatic control valves.

1. Why does the double seat valve oscillate easily when working 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 T-shaped filter 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 can easily cause valve 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, the disadvantage of its protrusion 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 interception 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 straight stroke regulating valve has poor anti blocking function, while angle stroke valve has good anti blocking function?

The valve core of the straight stroke valve is vertically throttled, while the medium flows in and out horizontally. The flow channel inside the valve chamber must turn and reverse, making the flow path of the valve relatively complex (with an inverted "S" shape). In this way, there are many dead zones, and the head provides space for the precipitation of the medium. Over time, this can cause blockages. The direction of throttling of the angle stroke valve is the horizontal direction, where the medium flows in and out horizontally, easily carrying away unclean media. 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 function.

4. Why is the straight stroke regulating valve stem thinner?

It involves a simple mechanical principle: high sliding friction and low dynamic 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 that arises from this is that if the valve stem is thin, it is easy to bend and the packing life is short. The solution to this problem is to use a travel valve stem, which is a type of regulating valve with angular stroke. Its stem is 2-3 times thicker than a straight stroke stem, and a pressure gauge buffer tube is selected with long-life graphite packing. The stem stiffness is good, the packing life is long, and its friction torque and backlash are small.

5. Why is the blocking pressure difference of angular stroke valves large?

The blocking 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 rolling 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 erosion of rubber manifests as expansion, aging, and low strength. Butterfly valves and diaphragm valves lined with rubber have poor performance, and the quality of wear-resistant pipelines is due to the rubber's lack of corrosion resistance. 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 current method is to treat the ball valve with water, which can be used for 5-8 years.

7. Why should hard seals be used as much as possible for shut-off valves?

The lower the leakage of the blocking valve, the better. The leakage of the soft seal valve is the lowest, and the blocking effect is good, but it is not wear-resistant and has poor reliability. From the dual scale of small leakage and reliable sealing, adjustable shrinkage hole soft seal interception is not as good as hard seal interception. 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 petrochemical plants introduced in the 1980s, sleeve valves accounted for a large proportion. At that time, many people believed that sleeve valves could replace single and double seat valves, and hood type ventilation pipes became the second generation products. Until now, it is not the case that single seat valves, double seat valves, and sleeve valves are all 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. Since calculation is just a simple formula calculation, its essence lies not in the degree of the formula itself, but in whether the given process parameters are correct. The selection of basket filters involves a lot of content, and a slight carelessness can lead to improper selection, which not only results in the expenditure of manpower, material resources, and financial resources, but also has unsatisfactory usage effects, bringing 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, and the spring support hanger makes the actuator smaller in size and has greater thrust 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.