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    Common problems in the use of Valves

    Date:2020-12-21 14:45:01 Hits:474

      First, the control valve why the double seal valve can not be used as a cut-off valve?
      The advantage of double-seat valve spool is force balance structure and large allowable pressure difference, but its outstanding disadvantage is that the two sealing surfaces can not contact well at the same time, resulting in large leakage. If it is artificially and forcibly used in cutting off occasions, the effect is obviously not good, even if many improvements have been made for it (such as double sealing sleeve valve), it is not desirable.
      Why is the two-seat valve easy to oscillate when the small opening of the two-seat valve works?
      For a single core, when the medium is open, the stability of the valve is good; when the medium is flow-closed, the stability of the valve is poor. The double-seat valve has two spools, the lower spool is closed and the upper spool is open, so that the flow-closed spool can easily cause valve vibration when working with a small opening, which is the reason why the double-seat valve can not be used for small opening work.
      Third, what straight stroke regulating valve anti-blocking performance is poor, angle stroke valve anti-blocking performance is good?
      The straight-stroke valve spool is vertical throttling, while the medium flows in and out horizontally, so the flow channel in the valve cavity must turn upside down, so that the flow path of the valve becomes quite complex (such as inverted S-shaped). In this way, there are many dead zones, which provide space for the precipitation of the medium, which will cause blockage in the long run. The direction of the angular stroke valve throttle is horizontal, the medium flows in and out horizontally, it is easy to take away the unclean medium, at the same time, the flow path is simple, and there is little space for medium precipitation, so the angular stroke valve has good anti-blocking performance.
      Fourth, why is the cut-off pressure difference of angular stroke valves larger?
      The cut-off pressure difference of the angle stroke valve is large because the resultant force produced by the medium on the spool or valve plate produces a very small torque on the rotating shaft, so it can withstand a large pressure difference.
      Why is the straight stroke regulating valve stem thinner?
      It involves a simple mechanical principle: large sliding friction and small rolling friction. The stem of the straight-through valve moves up and down, and if the packing is pressed a little bit, it will wrap the stem very tightly, resulting in a large backlash. For this reason, the valve stem is designed to be very small, and the packing is often filled with tetrafluoro packing with low friction coefficient, in order to reduce the backlash, but the resulting problem is that the valve stem is thin, it is easy to bend, and the packing life is short. The best way to solve this problem is to use the travel valve stem, that is, the angular stroke type control valve, whose valve stem is 2 / 3 times thicker than the straight stroke valve stem, and chooses graphite packing with long life, which has good stem stiffness and long packing life. on the contrary, the friction torque is small and the backlash is small.
      Why does the desalted medium use rubber-lined butterfly valve and fluorine-lined diaphragm valve for short service life?
      The desalted medium contains low concentration of acid or alkali, which is more corrosive to rubber. The corrosion of rubber is characterized by expansion, aging and low strength, and the poor use effect of rubber-lined butterfly valve and diaphragm valve is essentially caused by the non-corrosion resistance of rubber. The rear rubber-lined diaphragm valve is improved to a fluorine-lined diaphragm valve with good corrosion resistance, but the diaphragm of the fluorine-lined diaphragm valve can not be folded up and down, resulting in mechanical damage and shorter service life of the valve. Now the best way is to use a special ball valve for water treatment, which can be used for 5 to 8 years.
      Why should the cut-off valve choose hard seal as far as possible?
      The lower the leakage, the better. The leakage of the soft seal valve is the lowest. The cutting effect is certainly good, but it is not wear-resistant and the reliability is poor. From the double standard of small leakage and reliable sealing, the soft seal cut-off is not as good as the hard seal cut-off. 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 cut-off valve.

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