First, why double seal valve can not be used as a shut-off valve The advantage of using two-seater valve spool is force balance structure, allowing the pressure to be large, and its prominent disadvantage is that the two sealing surfaces can not be good contact at the same time, resulting in a large leak. If it is artificially and purposely used to cut the occasion, apparently ineffective, even for it made many improvements (such as double seal sleeve valve), is not desirable. Second, why double seat valve easy to oscillation when the small opening work For the single core, when the medium is open type, the valve stability is good; when the medium is flow closed, the valve stability is poor. Double-seated valve has two spools, the lower spool in the flow closed, the valve spool is open, so that work in a small opening, the flow-closure valve spool is easy to cause the valve vibration, which is the double-seat valve Can not be used for a small degree of work reason. Third, what is the straight-stroke control valve anti-blocking performance is poor, the anti-blocking valve performance is good Stroke valve is a vertical straight throttle, while the medium is the level of flow in and out of the valve cavity must turn around the flow channel, so that the valve The flow path becomes quite complex (shape like inverted S). In this way, there are many dead zones that provide space for the precipitation of the medium over time, causing clogging. Angle valve stroke direction is the horizontal direction, the media into the level, the level of outflow, easy to clean media away, while the flow path is simple, medium precipitation space is also small, so the anti-blocking performance of the angular stroke valve. Fourth, why the angular stroke valve cut off the larger pressure? Angle stroke valve to cut off the larger pressure differential is because the media in the valve core or valve plate together on the torque generated by the rotating shaft is very small, therefore, it can withstand greater pressure. Fifth, why the straight stroke adjustment valve stem thin It involves a simple mechanical principle: sliding friction, rolling friction small. Straight travel valve stem up and down movement, the packing a little bit tight, it will be very tight stem package, resulting in greater backlash. To this end, the valve stem is designed to be very small, packing and PTFE friction coefficient is often small PTFE packing, in order to reduce backlash, but the problem is sent stem thin, easy to bend, filler life is short. Solve this problem, the best way is to travel with the valve stem, which is the type of angular travel control valve, the valve stem than the straight travel valve stem thick 2 to 3 times, and the choice of long life graphite packing, stem stiffness Good, long filler life, but the friction torque on the contrary, small backlash. Six, why desalinated water medium using rubber lined butterfly valve, lined diaphragm valve life is short? Desalinated water medium contains a low concentration of acid or alkali, they are more corrosive to rubber. Corrosion of rubber is manifested as swelling, aging, low strength, with rubber lining butterfly valve, diaphragm valve are poor effect is essentially the result of rubber intolerance corrosion. Liner rubber diaphragm valve improved corrosion-resistant performance of fluorine-lined diaphragm valve, but lined with fluorine diaphragm valve can not withstand the collapse of the upper and lower folded, resulting in mechanical damage, valve life shorter. Now the best way is to use special ball valve water treatment, it can be used to 5 to 8 years. Seven, why cut-off valve should be used as hard seal cut-off valve as required to leak the lower the better, soft-sealed valve leakage is the lowest, of course, cut off the effect, but not wear-resistant, poor reliability. From the leakage is small, sealed and reliable double standards, the soft seal cut off as good as the hard seal cut off. Such as full-featured ultra-light control valve, sealed and piled with wear-resistant alloy protection, high reliability, leakage rate of 10 to 7, has been able to meet the requirements of shut-off valve. This article Keywords: valve