First, why is it easy to oscillate when the double valve seat is working with small opening?
For a single core, when the medium is flow open, the valve stability is good; When the medium is flow closed type, the stability of the valve is poor. The double seat has two spool, the lower spool is in flow closed, the upper spool is in flow open, so that when the small opening is working, the flow closed spool is easy to cause the vibration of the valve, which is the reason why the upper seat can not be used for small opening work.
Second, why can't the double seal valve be used as a cut-off valve?

The advantage of the double seat valve core is the force balance structure, allowing the pressure difference to be large, and its prominent disadvantage is that the two sealing surfaces can not be in good contact at the same time, resulting in large leakage, if it is artificially and forcibly used for cutting occasions, obviously the effect is not good, even if many improvements have been made for it (such as the double sealing sleeve valve), it is not desirable.
Third, why is the anti-blocking performance of the straight stroke regulating valve poor, and the anti-blocking performance of the Angle stroke valve good?

The spool of the straight stroke valve is a vertical throttling, and the medium is a horizontal flow into and out, and the flow path in the valve chamber must turn and reverse, so that the flow path of the valve becomes quite complex (shape such as inverted S shape). In this way, there are many dead zones, providing space for the precipitation of the medium, in the long run, resulting in blockage, the direction of the throttle of the Angle stroke valve is the horizontal direction, the medium flows horizontally into and out horizontally, it is easy to take away the unclean medium, and the flow path is simple, and the space for the medium to precipitate is also very little, so the Angle stroke valve has good anti-blocking performance.
Four, why the straight stroke control valve stem is smaller?

It is designed on a simple mechanical principle: Sliding friction is large, rolling friction is small, straight stroke valve stem up and down movement, packing slightly pressed a little, it will put the valve stem package is very tight, resulting in a large return difference, for this reason, the valve stem design is very small, packing and commonly used friction coefficient of tetrafluoroidal packing, in order to reduce the return difference, but the resulting problem is that the valve stem is small, it is easy to bend, packing life is short. To solve this problem, the way is to use the rotary valve stem, that is, the regulating valve of the Angle stroke class, its valve stem is 2 to 3 times thicker than the valve stem of the straight stroke valve, and the selection of asbestos packing with long life, the valve stem stiffness is good, the packing life is long, and the friction torque is small and the return difference is small.
Five, why the Angle stroke valve cut off pressure difference is large?

The cutting pressure difference of the angular stroke valve is large because the resultant force generated by the medium on the spool or valve plate has a very small torque on the rotating shaft, so it can withstand a large pressure difference.

Six, why the use of demineralized water medium rubber lined butterfly valve, fluorine lined diaphragm valve short service life?

The desalted water medium contains low concentration of acid or alkali, which has a greater corrosion on the rubber head, and the corrosion of rubber is manifested as expansion, aging, low strength, and the use effect of rubber lined butterfly valve and diaphragm valve is poor, and the essence is that the rubber is not corrosion resistant. The rear rubber lined diaphragm valve is improved into a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve can not withstand the up and down folding and is broken, and the life of the valve becomes shorter. The current way is to treat the special ball valve with water, which can be used for 5 to 8 years.

Seven, why the sleeve valve instead of single and double seat valves did not succeed?

The sleeve valve came out in the 1960s, was widely used at home and abroad in the 1970s, and the sleeve valve accounted for a larger proportion of petrochemical devices introduced in the 1980s, at that time, many people believe that the sleeve valve can replace single and two-seat valves and become the second generation of products. Not so far. Single seat valve, double seat valve, sleeve valve are equally used. This is because the sleeve valve only improves the throttling form, stability and maintenance is better than the single-seat valve, but its weight, plugging and leakage indicators are consistent with the single and two-seat valves, how can it replace the single and two-seat valves? Therefore, it can only be shared.

Eight, why should the cut-off valve be as hard sealed as possible?

The lower the leakage requirement of the cut-off valve, the better, the leakage of the soft seal valve, the cutting effect is good, but it is not wear-resistant and the reliability is poor. From the leakage amount is small, sealing and reliable double standards, soft seal cut is not as good as hard seal cut off, such as full-function ultra-light control valve, sealing surface with wear-resistant alloy protection, high reliability, low leakage rate, can meet the requirements of the cut-off valve.

9. Why is selection more important than calculation?

Compared with the calculation and selection, the selection is more important and more complex, because the calculation is just a simple formula calculation, which itself is not the degree of the formula, but the accuracy of the given process parameters. The content of the modeling design is more, and a little careless, it will lead to improper selection, not only resulting in the waste of manpower, material resources and financial resources, but also the use effect is not ideal, bringing a number of use problems, such as reliability, life, operating quality and so on.

Ten, why will the piston actuator be used more and more in the pneumatic valve?

For pneumatic valves, the piston actuator can make full use of the air source pressure, so that the size of the actuator is smaller than the film type, the thrust is larger, and the O-ring in the piston is also more reliable than the film, so the use will be more and more.