10 problems often encountered in the use of valves

01 Why is the two-seat valve easy to oscillate when 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 valve has two spool, the lower spool is in the flow closed, the upper spool is in the 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 two-seat valve cannot be used for small opening work.
02 Why can't double seal valves be used as shut-off valves?
The advantage of the two-seat valve spool is that the force balance structure allows the pressure difference to be large, and its outstanding 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, it is obviously not effective, even if many improvements have been made for it (such as double-sealed sleeve valves), it is not advisable.
03 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" type).
04 Why is the stem of the straight stroke control valve thinner?
It involves a simple mechanical principle: large sliding friction and small rolling friction. The valve stem of the straight stroke valve moves up and down, and the packing is slightly pressed, it will wrap the valve stem very tightly, resulting in a larger return difference. For this reason, the valve stem is designed to be very small, and the packing is commonly used with a small friction coefficient of tetrafluoroidal packing in order to reduce the return difference, but the problem sent from this is that the valve stem is small, it is easy to bend, and the packing life is short. To solve this problem, the best 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 straight stroke valve stem, and the choice of long life graphite filler, the valve stem stiffness is good, the packing life is long, and the friction torque is small and the return difference is small.
05 Why is the cut-off pressure difference of Angle stroke valves 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.
06 Is the service life of rubber lined butterfly valve and fluorine lined diaphragm valve short?
The desalted water medium contains low concentrations of acids or bases, which are more corrosive to rubber. The corrosion of rubber is manifested as expansion, aging, low strength, and the use effect of butterfly valves and diaphragm valves lined with rubber is poor, and the essence is that 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 folding up and down and is broken, resulting in mechanical damage and the life of the valve is shortened. Now the best way is to treat the special ball valve with water, which can be used for 5 to 8 years.
07 Why should the cut-off valve be hard sealed as far as possible?
The lower the leakage requirement of the cut-off valve, the better, the leakage of the soft seal valve is perfect, and the cutting effect is of course good, but it is not wear-resistant and the reliability is poor. From the double standard of small leakage and reliable sealing, soft seal cutting is not as good as hard seal cutting. Such as full-function ultra-light control valve, sealed and stacked with wear-resistant alloy protection, high reliability, leakage rate up to 10-7, has been able to meet the requirements of the cut-off valve.
08 Sleeve valves instead of single and double seat valves but 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. Today, this is not the case, single-seat valves, two-seat valves, sleeve valves are used equally. 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.
09 Why is selection more important than calculation?
Calculation compared with selection, selection is much more important, much more complex. Because the calculation is only a simple formula calculation, its itself does not lie in the accuracy of the formula, but in the accuracy of the given process parameters.
10 Will piston actuators be used more and more in pneumatic valves?
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 its use will be more and more.