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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. The double seat valve has two valve cores, the lower valve core is closed, and the upper valve core is open. This way, when the valve is operated at a small opening, the flow-closed valve core can easily cause the vibration of the valve. This is the double seat valve. The reason why it cannot be used for small opening work.
2. Why can the double seal valve be used as a shut-off valve?
The advantage of the double-seat valve spool is its force balance structure, which allows a large pressure difference, and its outstanding disadvantage is that the two sealing surfaces cannot be in good contact at the same time, resulting in large leakage. If it is artificially and forcibly used in cutting off occasions, it is obviously not effective, and even if it is made with many improvements (such as double sealed sleeve valve), it is not desirable.
3, what is the direct stroke control valve anti-blocking performance is poor, angular stroke valve anti-blocking performance is good?
Straight stroke valve spool is vertical throttling, and the medium is horizontal flow in and out, the flow path in the valve cavity will inevitably turn and turn, so that the flow path of the valve becomes quite complex (such as inverted "S" type). In this way, there are many dead zones, which provide space for the sedimentation of the media and, over time, cause blockages. The direction of throttling valve throttle is the horizontal direction, the media flow into the horizontal outflow, easy to take the unclean media away, while the flow path is simple, the medium precipitation space is also very small, so the angle valve anti-blocking performance is good.
4. Why is the stem of the linear stroke valve thinner?
It involves a simple mechanical principle: large sliding friction and low rolling friction. The stem of the linear valve moves up and down, and the packing is pressed slightly. It will pack the valve stem tightly and generate a large return difference. For this reason, the valve stem is designed to be very small, and the filler is often a PTFE filler with a small friction coefficient so as to reduce the return difference, but the problem is that the valve stem is thin, it is easy to bend, and the filler life is short. To solve this problem, the best way is to use the trip valve stem, which is a quarter-rotor type valve. Its valve stem is 2 to 3 times thicker than the linear valve stem, and the long-life graphite filler is used. The stem rigidity is Well, long filler life, the friction torque is small, the difference is small.
5. Why is the differential pressure of the angle stroke valve larger?
The cut-off pressure difference of the angular stroke valve is larger because the resultant force generated by the medium on the valve plug or the valve plate generates a very small torque on the rotating shaft, so that it can withstand a large pressure difference.
6. Why does the use of rubber-lined butterfly valves for demineralized media and the service life of fluorine-lined diaphragm valves are short?
Demineralized water contains low concentrations of acids or bases that are highly corrosive to rubber. Corrosion of rubber is manifested as swelling, aging, and low strength. The effect of using rubber-lined butterfly valves and diaphragm valves is poor, and its essence is that rubber is not resistant to corrosion. The rear rubber-lined diaphragm valve was improved to be a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve could not withstand folding up and down and was broken, causing mechanical damage and shortening the life of the valve. The best way now is to treat the special ball valve with water. It can be used for 5 to 8 years.
7, why cut off the valve should try to use a hard seal?
The cut-off valve requires a lower leakage, the better, and the leakage of the soft-seal valve is the lowest. The cut-off effect is certainly good, but it is not wear-resistant and has poor reliability. From the double standards of small leaks, sealing and reliability, soft seal cutting is not as good as hard seal cutting. Such as full-featured ultra-light control valve, sealed and piled with wear-resistant alloy protection, high reliability, leakage rate of 10-7, has been able to meet the requirements of the shut-off valve.
8. Why doesn't the sleeve valve replace the single or double seat valve?
The sleeve valve that came out in the 1960s was widely used at home and abroad in the 1970s. The proportion of sleeve valves in petrochemical plants introduced in the 1980s was relatively large. At that time, many people believed that sleeve valves could replace single and double seat valves. Become the second generation product. 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 type, stability and maintenance better than 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.
9. Why is the selection more important than the calculation?
Compared with the calculation and selection, the selection is much more important and more complex. Because the calculation is just a simple formula calculation, it is not the accuracy of the formula itself, but the accuracy of the given process parameters. There are many items involved in the selection, and careless selection will result in improper selection. This not only results in a waste of manpower, material resources, and financial resources, but also results in unsatisfactory results. It brings with it certain problems in use, such as reliability, longevity, and operation. Quality and so on.
10. Why is there more and more use of piston actuators in pneumatic valves?
For pneumatic valves, the piston actuator can make full use of the air source pressure, make the actuator size smaller than the film type, and the thrust is greater. The O-ring in the piston is also more reliable than the film, so its use will become more and more. many.
To express my views on these two issues: I do not know if you understand that Shanghai Valve's V1000 series regulator does not, it successfully solved these problems. V1000 adopts a thick valve stem integrated structure, which is 2~5 times thicker than the valve stem of the conventional valve, and adopts the double guidance of the valve stem, which can realize the conditions of large pressure difference, which all depend on a strong execution structure. Power, so the V1000 uses a cylinder-type linear actuator, in order to stabilize the role of the cylinder and uses a double-acting form with spring return. If you are interested, we can discuss it in the forum.
1. Why does the double seat valve easily oscillate when it is operated at a small opening?