How to solve the ten common problems of valves

1, why cut off the valve should try to use a hard seal?

Cut off the valve requires a lower leakage, the better, the soft seal valve leakage is the lowest, of course, the cutting effect is good, but not wear and 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.

2. Why can the double seal valve be used as a shut-off valve?

The advantage of the two-seat valve spool is that the force balance structure 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 to cut off the occasion, obviously the effect is not good, even if it has made many improvements (such as double sealed sleeve valve), it is also not desirable.

3. Why does the double seat valve easily oscillate when it is operated at a small opening?

For a single core, when the medium is open-flow type, the valve has good stability; when the medium is 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.

4, 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 throttle valve throttle direction is the horizontal direction, the media flow into the horizontal outflow, easy to take away the dirty media, while the flow path is simple, the medium precipitation space is also very little, so the angle valve anti-blocking performance is good.

5, why the straight stroke valve stem smaller?

Straight stroke adjustment valve It involves a simple mechanical principle: large sliding friction, low rolling friction. The valve 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 in order 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 control valve, its stem is 2 to 3 times thicker than the straight stroke stem, and the use of long-life graphite filler, stem rigidity Well, long filler life, the friction torque is small, the difference is small.

6. Why is the pressure difference of the angle stroke valve larger?

The cut-off pressure difference of a quarter-turn type 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.

7. Why doesn't the sleeve valve replace the single or double seat valve?

The sleeve valves that came out in the 1960s were 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.

8. Why does the service life of the lined plastic butterfly valve and fluorine-lined diaphragm valve is short due to the desalinated water medium?

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 use of rubber-coated butterfly valves and diaphragm valves are all poor, and their essence is due to corrosion resistance of rubber. 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 stand 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.

9. 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.

10. 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 inappropriate selection. This not only results in a waste of manpower, material resources, and financial resources, but also results in unsatisfactory results, and brings with it certain problems in use, such as reliability, longevity, and operation. Quality and so on.